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Generation is a measure of electricity produced over time. Most electric power plants use some of the electricity they produce to operate the power plant.

Capacity is the maximum level of electric power (electricity) that a power plant can supply at a specific point in time under certain conditions.

Sales are the amount of electricity sold to customers over a period of time, and they account for most of U.S. electricity consumption.

More electricity is generated than sold, because some energy is lost (as heat) in transmission and distribution of electricity. In addition, some electricity consumers generate electricity and use most or all of it, and the amount they use is called direct use. These consumers include industrial, manufacturing, commercial, and institutional facilities, as well as homeowners who have their own electricity generators. The United States also exports and imports some electricity to and from Canada and Mexico. Total U.S. electricity consumption by end-use consumers is equal to U.S. retail sales of electricity plus direct use of electricity.

Utility scale includes electricity generation and capacity of generating units (generators) located at power plants with at least one megawatt (MW) of total electricity generating capacity.

Small scale includes generators with less than 1 MW of generating capacity that are usually at or near where the electricity is consumed. Most solar photovoltaic systems installed on building rooftops are small-scale systems.

Electricity generation

In 2020, net generation of electricity from utility-scale generators in the United States was about 4,009 billion kilowatthours (kWh) (or about 4 trillion kWh). EIA estimates that an additional 41.7 billion kWh (or about 0.04 trillion kWh) were generated with small-scale solar photovoltaic (PV) systems.

In 2020, about 60% of U.S. utility-scale electricity generation was produced from fossil fuels (coal, natural gas, and petroleum), about 20% was from nuclear energy, and about 20% was from renewable energy sources.

Electricity generating capacity

To ensure a steady supply of electricity to consumers, operators of the electric power system, or grid, call on electric power plants to produce and place the right amount of electricity on the grid at every moment to instantaneously meet and balance electricity demand.

Base load generating units normally supply all or part of the minimum, or base, demand (load) on the electric power grid. A base load generating unit runs continuously, producing electricity at a nearly constant rate throughout most of the day. Nuclear power plants generally operate as base load service, because of their low fuel costs and the technical limitations on load responsive operation. Geothermal and biomass units are also often operated in base load because of their low fuel costs. Many of the large hydro facilities, several coal plants, and an increasing number of natural gas-fired generators, particularly those in combined power applications, also supply base load power.

Peak load generating units help to meet electricity demand when demand is at its highest, or peak, such as in late afternoon and as when electricity use for air conditioning and heating increases during hot weather and cold weather respectively. These so-called peaking units are generally natural gas or petroleum fueled generators. In general, these generators are relatively inefficient and are costly to operate, but provide high- value service during peak demand periods. In some cases, pumped storage hydropower and conventional hydropower units also support grid operations by providing power during periods of peak demand.

Intermediate load generating units comprise the largest generating sector and provide load responsive operation between base load and peaking service. The demand profile varies over time and intermediate sources are in general technically and economically suited for following changes in load. Many energy sources and technologies are used in intermediate operation. Natural gas-fired combined cycle units, which currently provide more generation than any other technology, generally operate as intermediate sources.

Additional categories of electricity generators include

Intermittent renewable resource generators powered by wind and solar energy that generate electricity only when these resources are available (i.e., when it's windy or sunny). When these generators are operating, they tend to reduce the amount of electricity required from other generators to supply the electric power grid.

Electricity storage systems/facilities, including hydroelectric pumped storage, solar-thermal storage, batteries, flywheels, and compressed air systems. These systems typically use (or purchase) and store electricity that is generated during off-peak electricity demand periods (when electricity prices are relatively low), and they provide (or sell) the stored electricity during periods of high or peak electricity demand (when electricity prices are relatively high). Some facilities use electricity produced with intermittent renewable energy sources (wind and solar) when the renewable resource availability is high and provide the stored electricity when the renewable energy resource is low or unavailable. Nonhydro storage systems can also provide ancillary services to the electric power grid. Energy storage applications inherently use more electricity than they provide. Pumped-storage hydro systems use more electricity to pump water to water storage reservoirs than they produce with the stored water, and nonhydro storage systems have energy conversion and storage losses. Therefore electricity storage facilities have net negative electricity generation balances. Gross generation provides a better indicator about the activity level of storage technologies and is provided in the data releases of the EIA-923 Power Plant Operations Report.

Distributed generators are connected to the electricity grid, but they primarily supply some or all of the electricity demand of individual buildings or facilities. Sometimes, these systems may generate more electricity than the facility consumes, in which case the surplus electricity is sent to the grid. Most small-scale solar photovoltaic systems are distributed generators.

At the end of 2020, the United States had 1,117,475 MW-or about 1.12 billion kilowatts (kW)-of total utility-scale electricity generating capacity and about 27,724 MW-or nearly 0.03 billion kW-of small-scale solar photovoltaic electricity generating capacity.

Generating units fueled primarily with natural gas account for the largest share of utility-scale electricity generating capacity in the United States.

Energy sources for U.S. electricity generation

The mix of energy sources for U.S. electricity generation in the United States has changed over time, especially in recent years. Natural gas and renewable energy sources account for an increasing share of U.S. electricity generation, while coal-fired electricity generation has declined. In 1990, coal-fired power plants accounted for about 42% of total U.S. utility-scale electricity generating capacity and about 52% of total electricity generation. By the end of 2020, coal's share of electricity generating capacity was at 20% and coal accounted for 19% of total utility-scale electricity generation. During the same period, the share of natural gas-fired electricity generating capacity increased from 17% in 1990 to 43% in 2020, and its share of electricity generation more than tripled from 12% in 1990 to 40% in 2020.

Most U.S. nuclear and hydropower plants were built before 1990. Nuclear energy's share of total U.S. electricity generation has held steady at about 20% since 1990. Electricity generation from hydropower, historically the largest source of total annual utility-scale renewable electricity generation (until 2019), fluctuates from year to year because of precipitation patterns.

Total U.S. electricity generation from nonhydro renewables is increasing

Renewable electricity generation from sources other than hydropower has steadily increased in recent years, mainly because of additions to wind and solar generating capacity. Since 2014, total annual electricity generation from utility-scale nonhydro renewable sources has been greater than hydropower generation.

Wind energy's share of total utility-scale electricity generating capacity in the United States grew from 0.2% in 1990 to nearly 11% in 2020, and its share of total annual utility-scale electricity generation grew from less than 1% in 1990 to about 8% in 2020.

Although relatively small in terms of its share of total U.S. electricity capacity and generation, solar electricity generating capacity and generation have grown significantly in recent years. Utility-scale solar electricity generating capacity rose from about 314 MW-or 314,000 kW-in 1990 to about 47,848 MW (or about 48 million KW) at the end of 2020, of which about 96% was solar photovoltaic systems and 4% was solar thermal-electric systems. Solar energy's share of total U.S. utility-scale electricity generation in 2020 was about 2.3%, up from less than 0.1% in 1990. In addition, EIA estimates that at the end of 2020, there were 27,724 MW of small-scale solar photovoltaic generating capacity, and electricity generation from small-scale photovoltaic systems totaled was about 42 billion kWh.

Various factors influence the mix of energy sources for electricity generation

A decline in natural gas prices

State requirements to use more renewable energy sources

Availability of government and other financial incentives for building new renewable capacity

Federal air pollution emission regulations for power plants

Slowing electricity demand

Can be added in smaller increments to meet grid generating capacity requirements

Can respond more quickly to changes in hourly electricity demand

Generally have lower compliance costs with environmental regulations

Retail electricity sales

U.S. retail electricity sales to end-use customers totaled about 3,664 billion kWh-or 3.7 trillion kWh-in 2020, a decrease of about 147 billion kWh from 2019. Retail sales include net imports (imports minus exports) of electricity from Canada and Mexico.

Who sells electricity?

There are two general categories of electricity providers: full service providers, which sell bundled electricity services-energy (electricity) and delivery to end users, and other providers.

Full service providers may generate electricity from power plants that they own and sell the electricity to their customers and they may sell some of it to other types of providers. They may in turn purchase electricity from other full service providers or from independent power producers, which they sell to their customers. There are four general types of full service providers:

Investor owned utilities are electric utilities whose stock is publicly traded.

Public entities include municipalities, state power agencies, and municipal marketing authorities.

Federal entities are either owned or financed by the federal government.

Cooperatives are electric utilities owned by and operated for the benefit of the members of the cooperative.

Other providers market and sell electricity to the customers of full service providers or provide only electricity delivery services to consumers. They mostly include electricity marketers that operate in states where there is customer choice for selecting electricity providers. Full service providers deliver the electricity for the electricity marketers to consumers. There are also direct electricity transactions from independent power producers to (usually large) electricity consumers.

In addition to sales to end-use customers, electricity is also often traded on wholesale markets or through bilateral contracts.
Last updated: March 18, 2021

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Electricity generation, capacity, and sales in the United States - U.S. Energy Information Administration (EIA)

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Generation is a measure of electricity produced over time. Most electric power plants use some of the electricity they produce to operate the power plant. Capacity is the maximum level of electric power (electricity) that a power plant can supply at a specific point in time under certain conditions.

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Coal takes millions of years to form

Coal is a combustible black or brownish-black sedimentary rock with a high amount of carbon and hydrocarbons. Coal is classified as a nonrenewable energy source because it takes millions of years to form. Coal contains the energy stored by plants that lived hundreds of millions of years ago in swampy forests.

Layers of dirt and rock covered the plants over millions of years. The resulting pressure and heat turned the plants into the substance we call coal.

Types of coal

Coal is classified into four main types, or ranks: anthracite, bituminous, subbituminous, and lignite. The ranking depends on the types and amounts of carbon the coal contains and on the amount of heat energy the coal can produce. The rank of a coal deposit is determined by the amount of pressure and heat that acted on the plants over time.

Anthracite contains 86%-97% carbon and generally has the highest heating value of all ranks of coal. Anthracite accounted for less than 1% of the coal mined in the United States in 2021. All of the anthracite mines in the United States are in northeastern Pennsylvania. In the United States, anthracite is mainly used by the metals industry.

Bituminous coal contains 45%-86% carbon. Bituminous coal in the United States is between 100 million and 300 million years old. Bituminous coal is the most abundant rank of coal found in the United States, and it accounted for about 45% of total U.S. coal production in 2021. Bituminous coal is used to generate electricity and is an important fuel and raw material for making coking coal or use in the iron and steel industry. Bituminous coal was produced in at least 16 states in 2021, but five states accounted for about 78% of total bituminous production: West Virginia (30%), Pennsylvania (16%), Illinois (14%), Kentucky (10%), and Indiana (7%).

Subbituminous coal typically contains 35%-45% carbon, and it has a lower heating value than bituminous coal. Most subbituminous coal in the United States is at least 100 million years old. About 46% of total U.S. coal production in 2021 was subbituminous and about 88% was produced in Wyoming and 8% in Montana. The remainder was produced in Alaska, Colorado, and New Mexico.

Lignite contains 25%-35% carbon and has the lowest energy content of all coal ranks. Lignite coal deposits tend to be relatively young and were not subjected to extreme heat or pressure. Lignite is crumbly and has high moisture content, which contributes to its low heating value. Lignite accounted for 8% of total U.S. coal production in 2021. About 56% was mined in North Dakota and about 36% was mined in Texas. The other 8% was produced in Louisiana, Mississippi, and Montana. Lignite is mostly used to generate electricity. A facility in North Dakota also converts lignite to synthetic natural gas that is sent in natural gas pipelines to consumers in the eastern United States.
Last updated: October 19, 2022 with most recent data available at the time of update.

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How coal is formed and definitions of different types or ranks of coal: anthracite, bituminous, subbituminous, and lignite.

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In 2021, about 546 million short tons (MMst) of coal were consumed in the United States. On an energy content basis, this amount was equal to about 10.5 quadrillion British thermal units (Btu) and to about 10.8% of total U.S. energy consumption. This was the lowest amount since 1964 and the second-lowest percentage share after 2020 of total U.S. annual energy consumption since at least 1949. Although coal use was once common in the industrial, transportation, residential, and commercial sectors, today the main use of coal in the United States is to generate electricity. The electric power sector has accounted for the majority of U.S. coal consumption since 1961.

Electric power-501.4 MMst-91.9%

Industrial total-43.4 MMst-8.0%

Industrial coke plants-17.6 MMst-3.2%

Industrial combined heat and power-10.0 MMst-1.8%

Other industrial-15.9 MMst-2.9%

Commercial-0.8 MMst-0.1%

Residential and transportation-not available ²

On an energy content basis, U.S. coal consumption peaked in 2005, but the total annual tonnage of U.S. coal consumption peaked in 2007. Coal consumption declined in most years since then, mainly because of a decline in the use of coal for electricity generation.

Electric power

Coal-fired power plants burn coal to make steam and the steam turns turbines (machines for generating rotary mechanical power) to generate electricity. Many industries and businesses have their own power plants, and some use coal to generate electricity for their own use and mostly in combined heat and power plants. Learn more about U.S. electricity generation.

Industry

Many industries use coal and coal byproducts. The concrete and paper industries burn large amounts of coal to produce heat. The steel industry uses coal indirectly as coal coke to smelt iron ore into iron to make steel. The high temperatures created by burning coal coke give steel the strength and flexibility needed for bridges, buildings, and automobiles.

Blast furnace in a modern steel works

Source: BBC (copyrighted)

Converting coal into gas and liquids

Coal can be turned into gases and liquids that can be used as fuels or processed into chemicals to make other products. These gases or liquids are sometimes called synthetic fuels or synfuels. Synthetic fuels are made by heating coal in large vessels. These fuels produce fewer air pollutants when burned than burning coal directly.

In North Dakota, the Great Plains Synfuels Plant converts coal into synthetic natural gas (syngas). Syngas produced from coal can also be used to produce electricity and hydrogen. Currently, no commercially operating facilities in the United States produce liquids from coal, but coal has been converted to liquids in South Africa for decades.
Last updated: June 6, 2022, with the most recent data available at time of update; data for 2021 are preliminary.

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Use of coal - U.S. Energy Information Administration (EIA)

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In 2021, about 546 million short tons (MMst) of coal were consumed in the United States. On an energy content basis, this amount was equal to about 10.5 quadrillion British thermal units (Btu) and to about 10.8% of total U.S. energy consumption.

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Generation is a measure of electricity produced over time. Most electric power plants use some of the electricity they produce to operate the power plant.

Capacity is the maximum level of electric power (electricity) that a power plant can supply at a specific point in time under certain conditions.

Sales are the amount of electricity sold to customers over a period of time, and they account for most of U.S. electricity consumption.

More electricity is generated than sold, because some energy is lost (as heat) in transmission and distribution of electricity. In addition, some electricity consumers generate electricity and use most or all of it, and the amount they use is called direct use. These consumers include industrial, manufacturing, commercial, and institutional facilities, as well as homeowners who have their own electricity generators. The United States also exports and imports some electricity to and from Canada and Mexico. Total U.S. electricity consumption by end-use consumers is equal to U.S. retail sales of electricity plus direct use of electricity.

Utility scale includes electricity generation and capacity of generating units (generators) located at power plants with at least one megawatt (MW) of total electricity generating capacity.

Small scale includes generators with less than 1 MW of generating capacity that are usually at or near where the electricity is consumed. Most solar photovoltaic systems installed on building rooftops are small-scale systems.

Electricity generation

In 2020, net generation of electricity from utility-scale generators in the United States was about 4,009 billion kilowatthours (kWh) (or about 4 trillion kWh). EIA estimates that an additional 41.7 billion kWh (or about 0.04 trillion kWh) were generated with small-scale solar photovoltaic (PV) systems.

In 2020, about 60% of U.S. utility-scale electricity generation was produced from fossil fuels (coal, natural gas, and petroleum), about 20% was from nuclear energy, and about 20% was from renewable energy sources.

Electricity generating capacity

To ensure a steady supply of electricity to consumers, operators of the electric power system, or grid, call on electric power plants to produce and place the right amount of electricity on the grid at every moment to instantaneously meet and balance electricity demand.

Base load generating units normally supply all or part of the minimum, or base, demand (load) on the electric power grid. A base load generating unit runs continuously, producing electricity at a nearly constant rate throughout most of the day. Nuclear power plants generally operate as base load service, because of their low fuel costs and the technical limitations on load responsive operation. Geothermal and biomass units are also often operated in base load because of their low fuel costs. Many of the large hydro facilities, several coal plants, and an increasing number of natural gas-fired generators, particularly those in combined power applications, also supply base load power.

Peak load generating units help to meet electricity demand when demand is at its highest, or peak, such as in late afternoon and as when electricity use for air conditioning and heating increases during hot weather and cold weather respectively. These so-called peaking units are generally natural gas or petroleum fueled generators. In general, these generators are relatively inefficient and are costly to operate, but provide high- value service during peak demand periods. In some cases, pumped storage hydropower and conventional hydropower units also support grid operations by providing power during periods of peak demand.

Intermediate load generating units comprise the largest generating sector and provide load responsive operation between base load and peaking service. The demand profile varies over time and intermediate sources are in general technically and economically suited for following changes in load. Many energy sources and technologies are used in intermediate operation. Natural gas-fired combined cycle units, which currently provide more generation than any other technology, generally operate as intermediate sources.

Additional categories of electricity generators include

Intermittent renewable resource generators powered by wind and solar energy that generate electricity only when these resources are available (i.e., when it's windy or sunny). When these generators are operating, they tend to reduce the amount of electricity required from other generators to supply the electric power grid.

Electricity storage systems/facilities, including hydroelectric pumped storage, solar-thermal storage, batteries, flywheels, and compressed air systems. These systems typically use (or purchase) and store electricity that is generated during off-peak electricity demand periods (when electricity prices are relatively low), and they provide (or sell) the stored electricity during periods of high or peak electricity demand (when electricity prices are relatively high). Some facilities use electricity produced with intermittent renewable energy sources (wind and solar) when the renewable resource availability is high and provide the stored electricity when the renewable energy resource is low or unavailable. Nonhydro storage systems can also provide ancillary services to the electric power grid. Energy storage applications inherently use more electricity than they provide. Pumped-storage hydro systems use more electricity to pump water to water storage reservoirs than they produce with the stored water, and nonhydro storage systems have energy conversion and storage losses. Therefore electricity storage facilities have net negative electricity generation balances. Gross generation provides a better indicator about the activity level of storage technologies and is provided in the data releases of the EIA-923 Power Plant Operations Report.

Distributed generators are connected to the electricity grid, but they primarily supply some or all of the electricity demand of individual buildings or facilities. Sometimes, these systems may generate more electricity than the facility consumes, in which case the surplus electricity is sent to the grid. Most small-scale solar photovoltaic systems are distributed generators.

At the end of 2020, the United States had 1,117,475 MW-or about 1.12 billion kilowatts (kW)-of total utility-scale electricity generating capacity and about 27,724 MW-or nearly 0.03 billion kW-of small-scale solar photovoltaic electricity generating capacity.

Generating units fueled primarily with natural gas account for the largest share of utility-scale electricity generating capacity in the United States.

Energy sources for U.S. electricity generation

The mix of energy sources for U.S. electricity generation in the United States has changed over time, especially in recent years. Natural gas and renewable energy sources account for an increasing share of U.S. electricity generation, while coal-fired electricity generation has declined. In 1990, coal-fired power plants accounted for about 42% of total U.S. utility-scale electricity generating capacity and about 52% of total electricity generation. By the end of 2020, coal's share of electricity generating capacity was at 20% and coal accounted for 19% of total utility-scale electricity generation. During the same period, the share of natural gas-fired electricity generating capacity increased from 17% in 1990 to 43% in 2020, and its share of electricity generation more than tripled from 12% in 1990 to 40% in 2020.

Most U.S. nuclear and hydropower plants were built before 1990. Nuclear energy's share of total U.S. electricity generation has held steady at about 20% since 1990. Electricity generation from hydropower, historically the largest source of total annual utility-scale renewable electricity generation (until 2019), fluctuates from year to year because of precipitation patterns.

Total U.S. electricity generation from nonhydro renewables is increasing

Renewable electricity generation from sources other than hydropower has steadily increased in recent years, mainly because of additions to wind and solar generating capacity. Since 2014, total annual electricity generation from utility-scale nonhydro renewable sources has been greater than hydropower generation.

Wind energy's share of total utility-scale electricity generating capacity in the United States grew from 0.2% in 1990 to nearly 11% in 2020, and its share of total annual utility-scale electricity generation grew from less than 1% in 1990 to about 8% in 2020.

Although relatively small in terms of its share of total U.S. electricity capacity and generation, solar electricity generating capacity and generation have grown significantly in recent years. Utility-scale solar electricity generating capacity rose from about 314 MW-or 314,000 kW-in 1990 to about 47,848 MW (or about 48 million KW) at the end of 2020, of which about 96% was solar photovoltaic systems and 4% was solar thermal-electric systems. Solar energy's share of total U.S. utility-scale electricity generation in 2020 was about 2.3%, up from less than 0.1% in 1990. In addition, EIA estimates that at the end of 2020, there were 27,724 MW of small-scale solar photovoltaic generating capacity, and electricity generation from small-scale photovoltaic systems totaled was about 42 billion kWh.

Various factors influence the mix of energy sources for electricity generation

A decline in natural gas prices

State requirements to use more renewable energy sources

Availability of government and other financial incentives for building new renewable capacity

Federal air pollution emission regulations for power plants

Slowing electricity demand

Can be added in smaller increments to meet grid generating capacity requirements

Can respond more quickly to changes in hourly electricity demand

Generally have lower compliance costs with environmental regulations

Retail electricity sales

U.S. retail electricity sales to end-use customers totaled about 3,664 billion kWh-or 3.7 trillion kWh-in 2020, a decrease of about 147 billion kWh from 2019. Retail sales include net imports (imports minus exports) of electricity from Canada and Mexico.

Who sells electricity?

There are two general categories of electricity providers: full service providers, which sell bundled electricity services-energy (electricity) and delivery to end users, and other providers.

Full service providers may generate electricity from power plants that they own and sell the electricity to their customers and they may sell some of it to other types of providers. They may in turn purchase electricity from other full service providers or from independent power producers, which they sell to their customers. There are four general types of full service providers:

Investor owned utilities are electric utilities whose stock is publicly traded.

Public entities include municipalities, state power agencies, and municipal marketing authorities.

Federal entities are either owned or financed by the federal government.

Cooperatives are electric utilities owned by and operated for the benefit of the members of the cooperative.

Other providers market and sell electricity to the customers of full service providers or provide only electricity delivery services to consumers. They mostly include electricity marketers that operate in states where there is customer choice for selecting electricity providers. Full service providers deliver the electricity for the electricity marketers to consumers. There are also direct electricity transactions from independent power producers to (usually large) electricity consumers.

In addition to sales to end-use customers, electricity is also often traded on wholesale markets or through bilateral contracts.
Last updated: March 18, 2021

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Electricity generation, capacity, and sales in the United States - U.S. Energy Information Administration (EIA)

# data[].attributes.attachment_link.description
Generation is a measure of electricity produced over time. Most electric power plants use some of the electricity they produce to operate the power plant. Capacity is the maximum level of electric power (electricity) that a power plant can supply at a specific point in time under certain conditions.

# data[].attributes.attachment_link.readable_text
Generation is a measure of electricity produced over time. Most electric power plants use some of the electricity they produce to operate the power plant.

Capacity is the maximum level of electric power (electricity) that a power plant can supply at a specific point in time under certain conditions.

Sales are the amount of electricity sold to customers over a period of time, and they account for most of U.S. electricity consumption.

More electricity is generated than sold, because some energy is lost (as heat) in transmission and distribution of electricity. In addition, some electricity consumers generate electricity and use most or all of it, and the amount they use is called direct use. These consumers include industrial, manufacturing, commercial, and institutional facilities, as well as homeowners who have their own electricity generators. The United States also exports and imports some electricity to and from Canada and Mexico. Total U.S. electricity consumption by end-use consumers is equal to U.S. retail sales of electricity plus direct use of electricity.

Utility scale includes electricity generation and capacity of generating units (generators) located at power plants with at least one megawatt (MW) of total electricity generating capacity.

Small scale includes generators with less than 1 MW of generating capacity that are usually at or near where the electricity is consumed. Most solar photovoltaic systems installed on building rooftops are small-scale systems.

Electricity generation

In 2020, net generation of electricity from utility-scale generators in the United States was about 4,009 billion kilowatthours (kWh) (or about 4 trillion kWh). EIA estimates that an additional 41.7 billion kWh (or about 0.04 trillion kWh) were generated with small-scale solar photovoltaic (PV) systems.

In 2020, about 60% of U.S. utility-scale electricity generation was produced from fossil fuels (coal, natural gas, and petroleum), about 20% was from nuclear energy, and about 20% was from renewable energy sources.

Electricity generating capacity

To ensure a steady supply of electricity to consumers, operators of the electric power system, or grid, call on electric power plants to produce and place the right amount of electricity on the grid at every moment to instantaneously meet and balance electricity demand.

Base load generating units normally supply all or part of the minimum, or base, demand (load) on the electric power grid. A base load generating unit runs continuously, producing electricity at a nearly constant rate throughout most of the day. Nuclear power plants generally operate as base load service, because of their low fuel costs and the technical limitations on load responsive operation. Geothermal and biomass units are also often operated in base load because of their low fuel costs. Many of the large hydro facilities, several coal plants, and an increasing number of natural gas-fired generators, particularly those in combined power applications, also supply base load power.

Peak load generating units help to meet electricity demand when demand is at its highest, or peak, such as in late afternoon and as when electricity use for air conditioning and heating increases during hot weather and cold weather respectively. These so-called peaking units are generally natural gas or petroleum fueled generators. In general, these generators are relatively inefficient and are costly to operate, but provide high- value service during peak demand periods. In some cases, pumped storage hydropower and conventional hydropower units also support grid operations by providing power during periods of peak demand.

Intermediate load generating units comprise the largest generating sector and provide load responsive operation between base load and peaking service. The demand profile varies over time and intermediate sources are in general technically and economically suited for following changes in load. Many energy sources and technologies are used in intermediate operation. Natural gas-fired combined cycle units, which currently provide more generation than any other technology, generally operate as intermediate sources.

Additional categories of electricity generators include

Intermittent renewable resource generators powered by wind and solar energy that generate electricity only when these resources are available (i.e., when it's windy or sunny). When these generators are operating, they tend to reduce the amount of electricity required from other generators to supply the electric power grid.

Electricity storage systems/facilities, including hydroelectric pumped storage, solar-thermal storage, batteries, flywheels, and compressed air systems. These systems typically use (or purchase) and store electricity that is generated during off-peak electricity demand periods (when electricity prices are relatively low), and they provide (or sell) the stored electricity during periods of high or peak electricity demand (when electricity prices are relatively high). Some facilities use electricity produced with intermittent renewable energy sources (wind and solar) when the renewable resource availability is high and provide the stored electricity when the renewable energy resource is low or unavailable. Nonhydro storage systems can also provide ancillary services to the electric power grid. Energy storage applications inherently use more electricity than they provide. Pumped-storage hydro systems use more electricity to pump water to water storage reservoirs than they produce with the stored water, and nonhydro storage systems have energy conversion and storage losses. Therefore electricity storage facilities have net negative electricity generation balances. Gross generation provides a better indicator about the activity level of storage technologies and is provided in the data releases of the EIA-923 Power Plant Operations Report.

Distributed generators are connected to the electricity grid, but they primarily supply some or all of the electricity demand of individual buildings or facilities. Sometimes, these systems may generate more electricity than the facility consumes, in which case the surplus electricity is sent to the grid. Most small-scale solar photovoltaic systems are distributed generators.

At the end of 2020, the United States had 1,117,475 MW-or about 1.12 billion kilowatts (kW)-of total utility-scale electricity generating capacity and about 27,724 MW-or nearly 0.03 billion kW-of small-scale solar photovoltaic electricity generating capacity.

Generating units fueled primarily with natural gas account for the largest share of utility-scale electricity generating capacity in the United States.

Energy sources for U.S. electricity generation

The mix of energy sources for U.S. electricity generation in the United States has changed over time, especially in recent years. Natural gas and renewable energy sources account for an increasing share of U.S. electricity generation, while coal-fired electricity generation has declined. In 1990, coal-fired power plants accounted for about 42% of total U.S. utility-scale electricity generating capacity and about 52% of total electricity generation. By the end of 2020, coal's share of electricity generating capacity was at 20% and coal accounted for 19% of total utility-scale electricity generation. During the same period, the share of natural gas-fired electricity generating capacity increased from 17% in 1990 to 43% in 2020, and its share of electricity generation more than tripled from 12% in 1990 to 40% in 2020.

Most U.S. nuclear and hydropower plants were built before 1990. Nuclear energy's share of total U.S. electricity generation has held steady at about 20% since 1990. Electricity generation from hydropower, historically the largest source of total annual utility-scale renewable electricity generation (until 2019), fluctuates from year to year because of precipitation patterns.

Total U.S. electricity generation from nonhydro renewables is increasing

Renewable electricity generation from sources other than hydropower has steadily increased in recent years, mainly because of additions to wind and solar generating capacity. Since 2014, total annual electricity generation from utility-scale nonhydro renewable sources has been greater than hydropower generation.

Wind energy's share of total utility-scale electricity generating capacity in the United States grew from 0.2% in 1990 to nearly 11% in 2020, and its share of total annual utility-scale electricity generation grew from less than 1% in 1990 to about 8% in 2020.

Although relatively small in terms of its share of total U.S. electricity capacity and generation, solar electricity generating capacity and generation have grown significantly in recent years. Utility-scale solar electricity generating capacity rose from about 314 MW-or 314,000 kW-in 1990 to about 47,848 MW (or about 48 million KW) at the end of 2020, of which about 96% was solar photovoltaic systems and 4% was solar thermal-electric systems. Solar energy's share of total U.S. utility-scale electricity generation in 2020 was about 2.3%, up from less than 0.1% in 1990. In addition, EIA estimates that at the end of 2020, there were 27,724 MW of small-scale solar photovoltaic generating capacity, and electricity generation from small-scale photovoltaic systems totaled was about 42 billion kWh.

Various factors influence the mix of energy sources for electricity generation

A decline in natural gas prices

State requirements to use more renewable energy sources

Availability of government and other financial incentives for building new renewable capacity

Federal air pollution emission regulations for power plants

Slowing electricity demand

Can be added in smaller increments to meet grid generating capacity requirements

Can respond more quickly to changes in hourly electricity demand

Generally have lower compliance costs with environmental regulations

Retail electricity sales

U.S. retail electricity sales to end-use customers totaled about 3,664 billion kWh-or 3.7 trillion kWh-in 2020, a decrease of about 147 billion kWh from 2019. Retail sales include net imports (imports minus exports) of electricity from Canada and Mexico.

Who sells electricity?

There are two general categories of electricity providers: full service providers, which sell bundled electricity services-energy (electricity) and delivery to end users, and other providers.

Full service providers may generate electricity from power plants that they own and sell the electricity to their customers and they may sell some of it to other types of providers. They may in turn purchase electricity from other full service providers or from independent power producers, which they sell to their customers. There are four general types of full service providers:

Investor owned utilities are electric utilities whose stock is publicly traded.

Public entities include municipalities, state power agencies, and municipal marketing authorities.

Federal entities are either owned or financed by the federal government.

Cooperatives are electric utilities owned by and operated for the benefit of the members of the cooperative.

Other providers market and sell electricity to the customers of full service providers or provide only electricity delivery services to consumers. They mostly include electricity marketers that operate in states where there is customer choice for selecting electricity providers. Full service providers deliver the electricity for the electricity marketers to consumers. There are also direct electricity transactions from independent power producers to (usually large) electricity consumers.

In addition to sales to end-use customers, electricity is also often traded on wholesale markets or through bilateral contracts.
Last updated: March 18, 2021

# data[].attributes.attachment_link.title
Electricity generation, capacity, and sales in the United States - U.S. Energy Information Administration (EIA)

# data[].attributes.attachment_link.description
Generation is a measure of electricity produced over time. Most electric power plants use some of the electricity they produce to operate the power plant. Capacity is the maximum level of electric power (electricity) that a power plant can supply at a specific point in time under certain conditions.

# data[].attributes.attachment_link.readable_text
Generation is a measure of electricity produced over time. Most electric power plants use some of the electricity they produce to operate the power plant.

Capacity is the maximum level of electric power (electricity) that a power plant can supply at a specific point in time under certain conditions.

Sales are the amount of electricity sold to customers over a period of time, and they account for most of U.S. electricity consumption.

More electricity is generated than sold, because some energy is lost (as heat) in transmission and distribution of electricity. In addition, some electricity consumers generate electricity and use most or all of it, and the amount they use is called direct use. These consumers include industrial, manufacturing, commercial, and institutional facilities, as well as homeowners who have their own electricity generators. The United States also exports and imports some electricity to and from Canada and Mexico. Total U.S. electricity consumption by end-use consumers is equal to U.S. retail sales of electricity plus direct use of electricity.

Utility scale includes electricity generation and capacity of generating units (generators) located at power plants with at least one megawatt (MW) of total electricity generating capacity.

Small scale includes generators with less than 1 MW of generating capacity that are usually at or near where the electricity is consumed. Most solar photovoltaic systems installed on building rooftops are small-scale systems.

Electricity generation

In 2020, net generation of electricity from utility-scale generators in the United States was about 4,009 billion kilowatthours (kWh) (or about 4 trillion kWh). EIA estimates that an additional 41.7 billion kWh (or about 0.04 trillion kWh) were generated with small-scale solar photovoltaic (PV) systems.

In 2020, about 60% of U.S. utility-scale electricity generation was produced from fossil fuels (coal, natural gas, and petroleum), about 20% was from nuclear energy, and about 20% was from renewable energy sources.

Electricity generating capacity

To ensure a steady supply of electricity to consumers, operators of the electric power system, or grid, call on electric power plants to produce and place the right amount of electricity on the grid at every moment to instantaneously meet and balance electricity demand.

Base load generating units normally supply all or part of the minimum, or base, demand (load) on the electric power grid. A base load generating unit runs continuously, producing electricity at a nearly constant rate throughout most of the day. Nuclear power plants generally operate as base load service, because of their low fuel costs and the technical limitations on load responsive operation. Geothermal and biomass units are also often operated in base load because of their low fuel costs. Many of the large hydro facilities, several coal plants, and an increasing number of natural gas-fired generators, particularly those in combined power applications, also supply base load power.

Peak load generating units help to meet electricity demand when demand is at its highest, or peak, such as in late afternoon and as when electricity use for air conditioning and heating increases during hot weather and cold weather respectively. These so-called peaking units are generally natural gas or petroleum fueled generators. In general, these generators are relatively inefficient and are costly to operate, but provide high- value service during peak demand periods. In some cases, pumped storage hydropower and conventional hydropower units also support grid operations by providing power during periods of peak demand.

Intermediate load generating units comprise the largest generating sector and provide load responsive operation between base load and peaking service. The demand profile varies over time and intermediate sources are in general technically and economically suited for following changes in load. Many energy sources and technologies are used in intermediate operation. Natural gas-fired combined cycle units, which currently provide more generation than any other technology, generally operate as intermediate sources.

Additional categories of electricity generators include

Intermittent renewable resource generators powered by wind and solar energy that generate electricity only when these resources are available (i.e., when it's windy or sunny). When these generators are operating, they tend to reduce the amount of electricity required from other generators to supply the electric power grid.

Electricity storage systems/facilities, including hydroelectric pumped storage, solar-thermal storage, batteries, flywheels, and compressed air systems. These systems typically use (or purchase) and store electricity that is generated during off-peak electricity demand periods (when electricity prices are relatively low), and they provide (or sell) the stored electricity during periods of high or peak electricity demand (when electricity prices are relatively high). Some facilities use electricity produced with intermittent renewable energy sources (wind and solar) when the renewable resource availability is high and provide the stored electricity when the renewable energy resource is low or unavailable. Nonhydro storage systems can also provide ancillary services to the electric power grid. Energy storage applications inherently use more electricity than they provide. Pumped-storage hydro systems use more electricity to pump water to water storage reservoirs than they produce with the stored water, and nonhydro storage systems have energy conversion and storage losses. Therefore electricity storage facilities have net negative electricity generation balances. Gross generation provides a better indicator about the activity level of storage technologies and is provided in the data releases of the EIA-923 Power Plant Operations Report.

Distributed generators are connected to the electricity grid, but they primarily supply some or all of the electricity demand of individual buildings or facilities. Sometimes, these systems may generate more electricity than the facility consumes, in which case the surplus electricity is sent to the grid. Most small-scale solar photovoltaic systems are distributed generators.

At the end of 2020, the United States had 1,117,475 MW-or about 1.12 billion kilowatts (kW)-of total utility-scale electricity generating capacity and about 27,724 MW-or nearly 0.03 billion kW-of small-scale solar photovoltaic electricity generating capacity.

Generating units fueled primarily with natural gas account for the largest share of utility-scale electricity generating capacity in the United States.

Energy sources for U.S. electricity generation

The mix of energy sources for U.S. electricity generation in the United States has changed over time, especially in recent years. Natural gas and renewable energy sources account for an increasing share of U.S. electricity generation, while coal-fired electricity generation has declined. In 1990, coal-fired power plants accounted for about 42% of total U.S. utility-scale electricity generating capacity and about 52% of total electricity generation. By the end of 2020, coal's share of electricity generating capacity was at 20% and coal accounted for 19% of total utility-scale electricity generation. During the same period, the share of natural gas-fired electricity generating capacity increased from 17% in 1990 to 43% in 2020, and its share of electricity generation more than tripled from 12% in 1990 to 40% in 2020.

Most U.S. nuclear and hydropower plants were built before 1990. Nuclear energy's share of total U.S. electricity generation has held steady at about 20% since 1990. Electricity generation from hydropower, historically the largest source of total annual utility-scale renewable electricity generation (until 2019), fluctuates from year to year because of precipitation patterns.

Total U.S. electricity generation from nonhydro renewables is increasing

Renewable electricity generation from sources other than hydropower has steadily increased in recent years, mainly because of additions to wind and solar generating capacity. Since 2014, total annual electricity generation from utility-scale nonhydro renewable sources has been greater than hydropower generation.

Wind energy's share of total utility-scale electricity generating capacity in the United States grew from 0.2% in 1990 to nearly 11% in 2020, and its share of total annual utility-scale electricity generation grew from less than 1% in 1990 to about 8% in 2020.

Although relatively small in terms of its share of total U.S. electricity capacity and generation, solar electricity generating capacity and generation have grown significantly in recent years. Utility-scale solar electricity generating capacity rose from about 314 MW-or 314,000 kW-in 1990 to about 47,848 MW (or about 48 million KW) at the end of 2020, of which about 96% was solar photovoltaic systems and 4% was solar thermal-electric systems. Solar energy's share of total U.S. utility-scale electricity generation in 2020 was about 2.3%, up from less than 0.1% in 1990. In addition, EIA estimates that at the end of 2020, there were 27,724 MW of small-scale solar photovoltaic generating capacity, and electricity generation from small-scale photovoltaic systems totaled was about 42 billion kWh.

Various factors influence the mix of energy sources for electricity generation

A decline in natural gas prices

State requirements to use more renewable energy sources

Availability of government and other financial incentives for building new renewable capacity

Federal air pollution emission regulations for power plants

Slowing electricity demand

Can be added in smaller increments to meet grid generating capacity requirements

Can respond more quickly to changes in hourly electricity demand

Generally have lower compliance costs with environmental regulations

Retail electricity sales

U.S. retail electricity sales to end-use customers totaled about 3,664 billion kWh-or 3.7 trillion kWh-in 2020, a decrease of about 147 billion kWh from 2019. Retail sales include net imports (imports minus exports) of electricity from Canada and Mexico.

Who sells electricity?

There are two general categories of electricity providers: full service providers, which sell bundled electricity services-energy (electricity) and delivery to end users, and other providers.

Full service providers may generate electricity from power plants that they own and sell the electricity to their customers and they may sell some of it to other types of providers. They may in turn purchase electricity from other full service providers or from independent power producers, which they sell to their customers. There are four general types of full service providers:

Investor owned utilities are electric utilities whose stock is publicly traded.

Public entities include municipalities, state power agencies, and municipal marketing authorities.

Federal entities are either owned or financed by the federal government.

Cooperatives are electric utilities owned by and operated for the benefit of the members of the cooperative.

Other providers market and sell electricity to the customers of full service providers or provide only electricity delivery services to consumers. They mostly include electricity marketers that operate in states where there is customer choice for selecting electricity providers. Full service providers deliver the electricity for the electricity marketers to consumers. There are also direct electricity transactions from independent power producers to (usually large) electricity consumers.

In addition to sales to end-use customers, electricity is also often traded on wholesale markets or through bilateral contracts.
Last updated: March 18, 2021

# data[].attributes.attachment_link.title
Electricity generation, capacity, and sales in the United States - U.S. Energy Information Administration (EIA)

# data[].attributes.attachment_link.description
Generation is a measure of electricity produced over time. Most electric power plants use some of the electricity they produce to operate the power plant. Capacity is the maximum level of electric power (electricity) that a power plant can supply at a specific point in time under certain conditions.

# data[].attributes.attachment_link.readable_text
Generation is a measure of electricity produced over time. Most electric power plants use some of the electricity they produce to operate the power plant.

Capacity is the maximum level of electric power (electricity) that a power plant can supply at a specific point in time under certain conditions.

Sales are the amount of electricity sold to customers over a period of time, and they account for most of U.S. electricity consumption.

More electricity is generated than sold, because some energy is lost (as heat) in transmission and distribution of electricity. In addition, some electricity consumers generate electricity and use most or all of it, and the amount they use is called direct use. These consumers include industrial, manufacturing, commercial, and institutional facilities, as well as homeowners who have their own electricity generators. The United States also exports and imports some electricity to and from Canada and Mexico. Total U.S. electricity consumption by end-use consumers is equal to U.S. retail sales of electricity plus direct use of electricity.

Utility scale includes electricity generation and capacity of generating units (generators) located at power plants with at least one megawatt (MW) of total electricity generating capacity.

Small scale includes generators with less than 1 MW of generating capacity that are usually at or near where the electricity is consumed. Most solar photovoltaic systems installed on building rooftops are small-scale systems.

Electricity generation

In 2020, net generation of electricity from utility-scale generators in the United States was about 4,009 billion kilowatthours (kWh) (or about 4 trillion kWh). EIA estimates that an additional 41.7 billion kWh (or about 0.04 trillion kWh) were generated with small-scale solar photovoltaic (PV) systems.

In 2020, about 60% of U.S. utility-scale electricity generation was produced from fossil fuels (coal, natural gas, and petroleum), about 20% was from nuclear energy, and about 20% was from renewable energy sources.

Electricity generating capacity

To ensure a steady supply of electricity to consumers, operators of the electric power system, or grid, call on electric power plants to produce and place the right amount of electricity on the grid at every moment to instantaneously meet and balance electricity demand.

Base load generating units normally supply all or part of the minimum, or base, demand (load) on the electric power grid. A base load generating unit runs continuously, producing electricity at a nearly constant rate throughout most of the day. Nuclear power plants generally operate as base load service, because of their low fuel costs and the technical limitations on load responsive operation. Geothermal and biomass units are also often operated in base load because of their low fuel costs. Many of the large hydro facilities, several coal plants, and an increasing number of natural gas-fired generators, particularly those in combined power applications, also supply base load power.

Peak load generating units help to meet electricity demand when demand is at its highest, or peak, such as in late afternoon and as when electricity use for air conditioning and heating increases during hot weather and cold weather respectively. These so-called peaking units are generally natural gas or petroleum fueled generators. In general, these generators are relatively inefficient and are costly to operate, but provide high- value service during peak demand periods. In some cases, pumped storage hydropower and conventional hydropower units also support grid operations by providing power during periods of peak demand.

Intermediate load generating units comprise the largest generating sector and provide load responsive operation between base load and peaking service. The demand profile varies over time and intermediate sources are in general technically and economically suited for following changes in load. Many energy sources and technologies are used in intermediate operation. Natural gas-fired combined cycle units, which currently provide more generation than any other technology, generally operate as intermediate sources.

Additional categories of electricity generators include

Intermittent renewable resource generators powered by wind and solar energy that generate electricity only when these resources are available (i.e., when it's windy or sunny). When these generators are operating, they tend to reduce the amount of electricity required from other generators to supply the electric power grid.

Electricity storage systems/facilities, including hydroelectric pumped storage, solar-thermal storage, batteries, flywheels, and compressed air systems. These systems typically use (or purchase) and store electricity that is generated during off-peak electricity demand periods (when electricity prices are relatively low), and they provide (or sell) the stored electricity during periods of high or peak electricity demand (when electricity prices are relatively high). Some facilities use electricity produced with intermittent renewable energy sources (wind and solar) when the renewable resource availability is high and provide the stored electricity when the renewable energy resource is low or unavailable. Nonhydro storage systems can also provide ancillary services to the electric power grid. Energy storage applications inherently use more electricity than they provide. Pumped-storage hydro systems use more electricity to pump water to water storage reservoirs than they produce with the stored water, and nonhydro storage systems have energy conversion and storage losses. Therefore electricity storage facilities have net negative electricity generation balances. Gross generation provides a better indicator about the activity level of storage technologies and is provided in the data releases of the EIA-923 Power Plant Operations Report.

Distributed generators are connected to the electricity grid, but they primarily supply some or all of the electricity demand of individual buildings or facilities. Sometimes, these systems may generate more electricity than the facility consumes, in which case the surplus electricity is sent to the grid. Most small-scale solar photovoltaic systems are distributed generators.

At the end of 2020, the United States had 1,117,475 MW-or about 1.12 billion kilowatts (kW)-of total utility-scale electricity generating capacity and about 27,724 MW-or nearly 0.03 billion kW-of small-scale solar photovoltaic electricity generating capacity.

Generating units fueled primarily with natural gas account for the largest share of utility-scale electricity generating capacity in the United States.

Energy sources for U.S. electricity generation

The mix of energy sources for U.S. electricity generation in the United States has changed over time, especially in recent years. Natural gas and renewable energy sources account for an increasing share of U.S. electricity generation, while coal-fired electricity generation has declined. In 1990, coal-fired power plants accounted for about 42% of total U.S. utility-scale electricity generating capacity and about 52% of total electricity generation. By the end of 2020, coal's share of electricity generating capacity was at 20% and coal accounted for 19% of total utility-scale electricity generation. During the same period, the share of natural gas-fired electricity generating capacity increased from 17% in 1990 to 43% in 2020, and its share of electricity generation more than tripled from 12% in 1990 to 40% in 2020.

Most U.S. nuclear and hydropower plants were built before 1990. Nuclear energy's share of total U.S. electricity generation has held steady at about 20% since 1990. Electricity generation from hydropower, historically the largest source of total annual utility-scale renewable electricity generation (until 2019), fluctuates from year to year because of precipitation patterns.

Total U.S. electricity generation from nonhydro renewables is increasing

Renewable electricity generation from sources other than hydropower has steadily increased in recent years, mainly because of additions to wind and solar generating capacity. Since 2014, total annual electricity generation from utility-scale nonhydro renewable sources has been greater than hydropower generation.

Wind energy's share of total utility-scale electricity generating capacity in the United States grew from 0.2% in 1990 to nearly 11% in 2020, and its share of total annual utility-scale electricity generation grew from less than 1% in 1990 to about 8% in 2020.

Although relatively small in terms of its share of total U.S. electricity capacity and generation, solar electricity generating capacity and generation have grown significantly in recent years. Utility-scale solar electricity generating capacity rose from about 314 MW-or 314,000 kW-in 1990 to about 47,848 MW (or about 48 million KW) at the end of 2020, of which about 96% was solar photovoltaic systems and 4% was solar thermal-electric systems. Solar energy's share of total U.S. utility-scale electricity generation in 2020 was about 2.3%, up from less than 0.1% in 1990. In addition, EIA estimates that at the end of 2020, there were 27,724 MW of small-scale solar photovoltaic generating capacity, and electricity generation from small-scale photovoltaic systems totaled was about 42 billion kWh.

Various factors influence the mix of energy sources for electricity generation

A decline in natural gas prices

State requirements to use more renewable energy sources

Availability of government and other financial incentives for building new renewable capacity

Federal air pollution emission regulations for power plants

Slowing electricity demand

Can be added in smaller increments to meet grid generating capacity requirements

Can respond more quickly to changes in hourly electricity demand

Generally have lower compliance costs with environmental regulations

Retail electricity sales

U.S. retail electricity sales to end-use customers totaled about 3,664 billion kWh-or 3.7 trillion kWh-in 2020, a decrease of about 147 billion kWh from 2019. Retail sales include net imports (imports minus exports) of electricity from Canada and Mexico.

Who sells electricity?

There are two general categories of electricity providers: full service providers, which sell bundled electricity services-energy (electricity) and delivery to end users, and other providers.

Full service providers may generate electricity from power plants that they own and sell the electricity to their customers and they may sell some of it to other types of providers. They may in turn purchase electricity from other full service providers or from independent power producers, which they sell to their customers. There are four general types of full service providers:

Investor owned utilities are electric utilities whose stock is publicly traded.

Public entities include municipalities, state power agencies, and municipal marketing authorities.

Federal entities are either owned or financed by the federal government.

Cooperatives are electric utilities owned by and operated for the benefit of the members of the cooperative.

Other providers market and sell electricity to the customers of full service providers or provide only electricity delivery services to consumers. They mostly include electricity marketers that operate in states where there is customer choice for selecting electricity providers. Full service providers deliver the electricity for the electricity marketers to consumers. There are also direct electricity transactions from independent power producers to (usually large) electricity consumers.

In addition to sales to end-use customers, electricity is also often traded on wholesale markets or through bilateral contracts.
Last updated: March 18, 2021

# data[].attributes.attachment_link.title
Electricity generation, capacity, and sales in the United States - U.S. Energy Information Administration (EIA)

# data[].attributes.attachment_link.description
Generation is a measure of electricity produced over time. Most electric power plants use some of the electricity they produce to operate the power plant. Capacity is the maximum level of electric power (electricity) that a power plant can supply at a specific point in time under certain conditions.

# data[].attributes.attachment_link.readable_text
Generation is a measure of electricity produced over time. Most electric power plants use some of the electricity they produce to operate the power plant.

Capacity is the maximum level of electric power (electricity) that a power plant can supply at a specific point in time under certain conditions.

Sales are the amount of electricity sold to customers over a period of time, and they account for most of U.S. electricity consumption.

More electricity is generated than sold, because some energy is lost (as heat) in transmission and distribution of electricity. In addition, some electricity consumers generate electricity and use most or all of it, and the amount they use is called direct use. These consumers include industrial, manufacturing, commercial, and institutional facilities, as well as homeowners who have their own electricity generators. The United States also exports and imports some electricity to and from Canada and Mexico. Total U.S. electricity consumption by end-use consumers is equal to U.S. retail sales of electricity plus direct use of electricity.

Utility scale includes electricity generation and capacity of generating units (generators) located at power plants with at least one megawatt (MW) of total electricity generating capacity.

Small scale includes generators with less than 1 MW of generating capacity that are usually at or near where the electricity is consumed. Most solar photovoltaic systems installed on building rooftops are small-scale systems.

Electricity generation

In 2020, net generation of electricity from utility-scale generators in the United States was about 4,009 billion kilowatthours (kWh) (or about 4 trillion kWh). EIA estimates that an additional 41.7 billion kWh (or about 0.04 trillion kWh) were generated with small-scale solar photovoltaic (PV) systems.

In 2020, about 60% of U.S. utility-scale electricity generation was produced from fossil fuels (coal, natural gas, and petroleum), about 20% was from nuclear energy, and about 20% was from renewable energy sources.

Electricity generating capacity

To ensure a steady supply of electricity to consumers, operators of the electric power system, or grid, call on electric power plants to produce and place the right amount of electricity on the grid at every moment to instantaneously meet and balance electricity demand.

Base load generating units normally supply all or part of the minimum, or base, demand (load) on the electric power grid. A base load generating unit runs continuously, producing electricity at a nearly constant rate throughout most of the day. Nuclear power plants generally operate as base load service, because of their low fuel costs and the technical limitations on load responsive operation. Geothermal and biomass units are also often operated in base load because of their low fuel costs. Many of the large hydro facilities, several coal plants, and an increasing number of natural gas-fired generators, particularly those in combined power applications, also supply base load power.

Peak load generating units help to meet electricity demand when demand is at its highest, or peak, such as in late afternoon and as when electricity use for air conditioning and heating increases during hot weather and cold weather respectively. These so-called peaking units are generally natural gas or petroleum fueled generators. In general, these generators are relatively inefficient and are costly to operate, but provide high- value service during peak demand periods. In some cases, pumped storage hydropower and conventional hydropower units also support grid operations by providing power during periods of peak demand.

Intermediate load generating units comprise the largest generating sector and provide load responsive operation between base load and peaking service. The demand profile varies over time and intermediate sources are in general technically and economically suited for following changes in load. Many energy sources and technologies are used in intermediate operation. Natural gas-fired combined cycle units, which currently provide more generation than any other technology, generally operate as intermediate sources.

Additional categories of electricity generators include

Intermittent renewable resource generators powered by wind and solar energy that generate electricity only when these resources are available (i.e., when it's windy or sunny). When these generators are operating, they tend to reduce the amount of electricity required from other generators to supply the electric power grid.

Electricity storage systems/facilities, including hydroelectric pumped storage, solar-thermal storage, batteries, flywheels, and compressed air systems. These systems typically use (or purchase) and store electricity that is generated during off-peak electricity demand periods (when electricity prices are relatively low), and they provide (or sell) the stored electricity during periods of high or peak electricity demand (when electricity prices are relatively high). Some facilities use electricity produced with intermittent renewable energy sources (wind and solar) when the renewable resource availability is high and provide the stored electricity when the renewable energy resource is low or unavailable. Nonhydro storage systems can also provide ancillary services to the electric power grid. Energy storage applications inherently use more electricity than they provide. Pumped-storage hydro systems use more electricity to pump water to water storage reservoirs than they produce with the stored water, and nonhydro storage systems have energy conversion and storage losses. Therefore electricity storage facilities have net negative electricity generation balances. Gross generation provides a better indicator about the activity level of storage technologies and is provided in the data releases of the EIA-923 Power Plant Operations Report.

Distributed generators are connected to the electricity grid, but they primarily supply some or all of the electricity demand of individual buildings or facilities. Sometimes, these systems may generate more electricity than the facility consumes, in which case the surplus electricity is sent to the grid. Most small-scale solar photovoltaic systems are distributed generators.

At the end of 2020, the United States had 1,117,475 MW-or about 1.12 billion kilowatts (kW)-of total utility-scale electricity generating capacity and about 27,724 MW-or nearly 0.03 billion kW-of small-scale solar photovoltaic electricity generating capacity.

Generating units fueled primarily with natural gas account for the largest share of utility-scale electricity generating capacity in the United States.

Energy sources for U.S. electricity generation

The mix of energy sources for U.S. electricity generation in the United States has changed over time, especially in recent years. Natural gas and renewable energy sources account for an increasing share of U.S. electricity generation, while coal-fired electricity generation has declined. In 1990, coal-fired power plants accounted for about 42% of total U.S. utility-scale electricity generating capacity and about 52% of total electricity generation. By the end of 2020, coal's share of electricity generating capacity was at 20% and coal accounted for 19% of total utility-scale electricity generation. During the same period, the share of natural gas-fired electricity generating capacity increased from 17% in 1990 to 43% in 2020, and its share of electricity generation more than tripled from 12% in 1990 to 40% in 2020.

Most U.S. nuclear and hydropower plants were built before 1990. Nuclear energy's share of total U.S. electricity generation has held steady at about 20% since 1990. Electricity generation from hydropower, historically the largest source of total annual utility-scale renewable electricity generation (until 2019), fluctuates from year to year because of precipitation patterns.

Total U.S. electricity generation from nonhydro renewables is increasing

Renewable electricity generation from sources other than hydropower has steadily increased in recent years, mainly because of additions to wind and solar generating capacity. Since 2014, total annual electricity generation from utility-scale nonhydro renewable sources has been greater than hydropower generation.

Wind energy's share of total utility-scale electricity generating capacity in the United States grew from 0.2% in 1990 to nearly 11% in 2020, and its share of total annual utility-scale electricity generation grew from less than 1% in 1990 to about 8% in 2020.

Although relatively small in terms of its share of total U.S. electricity capacity and generation, solar electricity generating capacity and generation have grown significantly in recent years. Utility-scale solar electricity generating capacity rose from about 314 MW-or 314,000 kW-in 1990 to about 47,848 MW (or about 48 million KW) at the end of 2020, of which about 96% was solar photovoltaic systems and 4% was solar thermal-electric systems. Solar energy's share of total U.S. utility-scale electricity generation in 2020 was about 2.3%, up from less than 0.1% in 1990. In addition, EIA estimates that at the end of 2020, there were 27,724 MW of small-scale solar photovoltaic generating capacity, and electricity generation from small-scale photovoltaic systems totaled was about 42 billion kWh.

Various factors influence the mix of energy sources for electricity generation

A decline in natural gas prices

State requirements to use more renewable energy sources

Availability of government and other financial incentives for building new renewable capacity

Federal air pollution emission regulations for power plants

Slowing electricity demand

Can be added in smaller increments to meet grid generating capacity requirements

Can respond more quickly to changes in hourly electricity demand

Generally have lower compliance costs with environmental regulations

Retail electricity sales

U.S. retail electricity sales to end-use customers totaled about 3,664 billion kWh-or 3.7 trillion kWh-in 2020, a decrease of about 147 billion kWh from 2019. Retail sales include net imports (imports minus exports) of electricity from Canada and Mexico.

Who sells electricity?

There are two general categories of electricity providers: full service providers, which sell bundled electricity services-energy (electricity) and delivery to end users, and other providers.

Full service providers may generate electricity from power plants that they own and sell the electricity to their customers and they may sell some of it to other types of providers. They may in turn purchase electricity from other full service providers or from independent power producers, which they sell to their customers. There are four general types of full service providers:

Investor owned utilities are electric utilities whose stock is publicly traded.

Public entities include municipalities, state power agencies, and municipal marketing authorities.

Federal entities are either owned or financed by the federal government.

Cooperatives are electric utilities owned by and operated for the benefit of the members of the cooperative.

Other providers market and sell electricity to the customers of full service providers or provide only electricity delivery services to consumers. They mostly include electricity marketers that operate in states where there is customer choice for selecting electricity providers. Full service providers deliver the electricity for the electricity marketers to consumers. There are also direct electricity transactions from independent power producers to (usually large) electricity consumers.

In addition to sales to end-use customers, electricity is also often traded on wholesale markets or through bilateral contracts.
Last updated: March 18, 2021

# data[].attributes.attachment_link.title
Electricity generation, capacity, and sales in the United States - U.S. Energy Information Administration (EIA)

# data[].attributes.attachment_link.description
Generation is a measure of electricity produced over time. Most electric power plants use some of the electricity they produce to operate the power plant. Capacity is the maximum level of electric power (electricity) that a power plant can supply at a specific point in time under certain conditions.

# data[].attributes.attachment_link.readable_text
Generation is a measure of electricity produced over time. Most electric power plants use some of the electricity they produce to operate the power plant.

Capacity is the maximum level of electric power (electricity) that a power plant can supply at a specific point in time under certain conditions.

Sales are the amount of electricity sold to customers over a period of time, and they account for most of U.S. electricity consumption.

More electricity is generated than sold, because some energy is lost (as heat) in transmission and distribution of electricity. In addition, some electricity consumers generate electricity and use most or all of it, and the amount they use is called direct use. These consumers include industrial, manufacturing, commercial, and institutional facilities, as well as homeowners who have their own electricity generators. The United States also exports and imports some electricity to and from Canada and Mexico. Total U.S. electricity consumption by end-use consumers is equal to U.S. retail sales of electricity plus direct use of electricity.

Utility scale includes electricity generation and capacity of generating units (generators) located at power plants with at least one megawatt (MW) of total electricity generating capacity.

Small scale includes generators with less than 1 MW of generating capacity that are usually at or near where the electricity is consumed. Most solar photovoltaic systems installed on building rooftops are small-scale systems.

Electricity generation

In 2020, net generation of electricity from utility-scale generators in the United States was about 4,009 billion kilowatthours (kWh) (or about 4 trillion kWh). EIA estimates that an additional 41.7 billion kWh (or about 0.04 trillion kWh) were generated with small-scale solar photovoltaic (PV) systems.

In 2020, about 60% of U.S. utility-scale electricity generation was produced from fossil fuels (coal, natural gas, and petroleum), about 20% was from nuclear energy, and about 20% was from renewable energy sources.

Electricity generating capacity

To ensure a steady supply of electricity to consumers, operators of the electric power system, or grid, call on electric power plants to produce and place the right amount of electricity on the grid at every moment to instantaneously meet and balance electricity demand.

Base load generating units normally supply all or part of the minimum, or base, demand (load) on the electric power grid. A base load generating unit runs continuously, producing electricity at a nearly constant rate throughout most of the day. Nuclear power plants generally operate as base load service, because of their low fuel costs and the technical limitations on load responsive operation. Geothermal and biomass units are also often operated in base load because of their low fuel costs. Many of the large hydro facilities, several coal plants, and an increasing number of natural gas-fired generators, particularly those in combined power applications, also supply base load power.

Peak load generating units help to meet electricity demand when demand is at its highest, or peak, such as in late afternoon and as when electricity use for air conditioning and heating increases during hot weather and cold weather respectively. These so-called peaking units are generally natural gas or petroleum fueled generators. In general, these generators are relatively inefficient and are costly to operate, but provide high- value service during peak demand periods. In some cases, pumped storage hydropower and conventional hydropower units also support grid operations by providing power during periods of peak demand.

Intermediate load generating units comprise the largest generating sector and provide load responsive operation between base load and peaking service. The demand profile varies over time and intermediate sources are in general technically and economically suited for following changes in load. Many energy sources and technologies are used in intermediate operation. Natural gas-fired combined cycle units, which currently provide more generation than any other technology, generally operate as intermediate sources.

Additional categories of electricity generators include

Intermittent renewable resource generators powered by wind and solar energy that generate electricity only when these resources are available (i.e., when it's windy or sunny). When these generators are operating, they tend to reduce the amount of electricity required from other generators to supply the electric power grid.

Electricity storage systems/facilities, including hydroelectric pumped storage, solar-thermal storage, batteries, flywheels, and compressed air systems. These systems typically use (or purchase) and store electricity that is generated during off-peak electricity demand periods (when electricity prices are relatively low), and they provide (or sell) the stored electricity during periods of high or peak electricity demand (when electricity prices are relatively high). Some facilities use electricity produced with intermittent renewable energy sources (wind and solar) when the renewable resource availability is high and provide the stored electricity when the renewable energy resource is low or unavailable. Nonhydro storage systems can also provide ancillary services to the electric power grid. Energy storage applications inherently use more electricity than they provide. Pumped-storage hydro systems use more electricity to pump water to water storage reservoirs than they produce with the stored water, and nonhydro storage systems have energy conversion and storage losses. Therefore electricity storage facilities have net negative electricity generation balances. Gross generation provides a better indicator about the activity level of storage technologies and is provided in the data releases of the EIA-923 Power Plant Operations Report.

Distributed generators are connected to the electricity grid, but they primarily supply some or all of the electricity demand of individual buildings or facilities. Sometimes, these systems may generate more electricity than the facility consumes, in which case the surplus electricity is sent to the grid. Most small-scale solar photovoltaic systems are distributed generators.

At the end of 2020, the United States had 1,117,475 MW-or about 1.12 billion kilowatts (kW)-of total utility-scale electricity generating capacity and about 27,724 MW-or nearly 0.03 billion kW-of small-scale solar photovoltaic electricity generating capacity.

Generating units fueled primarily with natural gas account for the largest share of utility-scale electricity generating capacity in the United States.

Energy sources for U.S. electricity generation

The mix of energy sources for U.S. electricity generation in the United States has changed over time, especially in recent years. Natural gas and renewable energy sources account for an increasing share of U.S. electricity generation, while coal-fired electricity generation has declined. In 1990, coal-fired power plants accounted for about 42% of total U.S. utility-scale electricity generating capacity and about 52% of total electricity generation. By the end of 2020, coal's share of electricity generating capacity was at 20% and coal accounted for 19% of total utility-scale electricity generation. During the same period, the share of natural gas-fired electricity generating capacity increased from 17% in 1990 to 43% in 2020, and its share of electricity generation more than tripled from 12% in 1990 to 40% in 2020.

Most U.S. nuclear and hydropower plants were built before 1990. Nuclear energy's share of total U.S. electricity generation has held steady at about 20% since 1990. Electricity generation from hydropower, historically the largest source of total annual utility-scale renewable electricity generation (until 2019), fluctuates from year to year because of precipitation patterns.

Total U.S. electricity generation from nonhydro renewables is increasing

Renewable electricity generation from sources other than hydropower has steadily increased in recent years, mainly because of additions to wind and solar generating capacity. Since 2014, total annual electricity generation from utility-scale nonhydro renewable sources has been greater than hydropower generation.

Wind energy's share of total utility-scale electricity generating capacity in the United States grew from 0.2% in 1990 to nearly 11% in 2020, and its share of total annual utility-scale electricity generation grew from less than 1% in 1990 to about 8% in 2020.

Although relatively small in terms of its share of total U.S. electricity capacity and generation, solar electricity generating capacity and generation have grown significantly in recent years. Utility-scale solar electricity generating capacity rose from about 314 MW-or 314,000 kW-in 1990 to about 47,848 MW (or about 48 million KW) at the end of 2020, of which about 96% was solar photovoltaic systems and 4% was solar thermal-electric systems. Solar energy's share of total U.S. utility-scale electricity generation in 2020 was about 2.3%, up from less than 0.1% in 1990. In addition, EIA estimates that at the end of 2020, there were 27,724 MW of small-scale solar photovoltaic generating capacity, and electricity generation from small-scale photovoltaic systems totaled was about 42 billion kWh.

Various factors influence the mix of energy sources for electricity generation

A decline in natural gas prices

State requirements to use more renewable energy sources

Availability of government and other financial incentives for building new renewable capacity

Federal air pollution emission regulations for power plants

Slowing electricity demand

Can be added in smaller increments to meet grid generating capacity requirements

Can respond more quickly to changes in hourly electricity demand

Generally have lower compliance costs with environmental regulations

Retail electricity sales

U.S. retail electricity sales to end-use customers totaled about 3,664 billion kWh-or 3.7 trillion kWh-in 2020, a decrease of about 147 billion kWh from 2019. Retail sales include net imports (imports minus exports) of electricity from Canada and Mexico.

Who sells electricity?

There are two general categories of electricity providers: full service providers, which sell bundled electricity services-energy (electricity) and delivery to end users, and other providers.

Full service providers may generate electricity from power plants that they own and sell the electricity to their customers and they may sell some of it to other types of providers. They may in turn purchase electricity from other full service providers or from independent power producers, which they sell to their customers. There are four general types of full service providers:

Investor owned utilities are electric utilities whose stock is publicly traded.

Public entities include municipalities, state power agencies, and municipal marketing authorities.

Federal entities are either owned or financed by the federal government.

Cooperatives are electric utilities owned by and operated for the benefit of the members of the cooperative.

Other providers market and sell electricity to the customers of full service providers or provide only electricity delivery services to consumers. They mostly include electricity marketers that operate in states where there is customer choice for selecting electricity providers. Full service providers deliver the electricity for the electricity marketers to consumers. There are also direct electricity transactions from independent power producers to (usually large) electricity consumers.

In addition to sales to end-use customers, electricity is also often traded on wholesale markets or through bilateral contracts.
Last updated: March 18, 2021

# data[].attributes.attachment_link.title
Electricity generation, capacity, and sales in the United States - U.S. Energy Information Administration (EIA)

# data[].attributes.attachment_link.description
Generation is a measure of electricity produced over time. Most electric power plants use some of the electricity they produce to operate the power plant. Capacity is the maximum level of electric power (electricity) that a power plant can supply at a specific point in time under certain conditions.

# data[].attributes.attachment_link.readable_text
Generation is a measure of electricity produced over time. Most electric power plants use some of the electricity they produce to operate the power plant.

Capacity is the maximum level of electric power (electricity) that a power plant can supply at a specific point in time under certain conditions.

Sales are the amount of electricity sold to customers over a period of time, and they account for most of U.S. electricity consumption.

More electricity is generated than sold, because some energy is lost (as heat) in transmission and distribution of electricity. In addition, some electricity consumers generate electricity and use most or all of it, and the amount they use is called direct use. These consumers include industrial, manufacturing, commercial, and institutional facilities, as well as homeowners who have their own electricity generators. The United States also exports and imports some electricity to and from Canada and Mexico. Total U.S. electricity consumption by end-use consumers is equal to U.S. retail sales of electricity plus direct use of electricity.

Utility scale includes electricity generation and capacity of generating units (generators) located at power plants with at least one megawatt (MW) of total electricity generating capacity.

Small scale includes generators with less than 1 MW of generating capacity that are usually at or near where the electricity is consumed. Most solar photovoltaic systems installed on building rooftops are small-scale systems.

Electricity generation

In 2020, net generation of electricity from utility-scale generators in the United States was about 4,009 billion kilowatthours (kWh) (or about 4 trillion kWh). EIA estimates that an additional 41.7 billion kWh (or about 0.04 trillion kWh) were generated with small-scale solar photovoltaic (PV) systems.

In 2020, about 60% of U.S. utility-scale electricity generation was produced from fossil fuels (coal, natural gas, and petroleum), about 20% was from nuclear energy, and about 20% was from renewable energy sources.

Electricity generating capacity

To ensure a steady supply of electricity to consumers, operators of the electric power system, or grid, call on electric power plants to produce and place the right amount of electricity on the grid at every moment to instantaneously meet and balance electricity demand.

Base load generating units normally supply all or part of the minimum, or base, demand (load) on the electric power grid. A base load generating unit runs continuously, producing electricity at a nearly constant rate throughout most of the day. Nuclear power plants generally operate as base load service, because of their low fuel costs and the technical limitations on load responsive operation. Geothermal and biomass units are also often operated in base load because of their low fuel costs. Many of the large hydro facilities, several coal plants, and an increasing number of natural gas-fired generators, particularly those in combined power applications, also supply base load power.

Peak load generating units help to meet electricity demand when demand is at its highest, or peak, such as in late afternoon and as when electricity use for air conditioning and heating increases during hot weather and cold weather respectively. These so-called peaking units are generally natural gas or petroleum fueled generators. In general, these generators are relatively inefficient and are costly to operate, but provide high- value service during peak demand periods. In some cases, pumped storage hydropower and conventional hydropower units also support grid operations by providing power during periods of peak demand.

Intermediate load generating units comprise the largest generating sector and provide load responsive operation between base load and peaking service. The demand profile varies over time and intermediate sources are in general technically and economically suited for following changes in load. Many energy sources and technologies are used in intermediate operation. Natural gas-fired combined cycle units, which currently provide more generation than any other technology, generally operate as intermediate sources.

Additional categories of electricity generators include

Intermittent renewable resource generators powered by wind and solar energy that generate electricity only when these resources are available (i.e., when it's windy or sunny). When these generators are operating, they tend to reduce the amount of electricity required from other generators to supply the electric power grid.

Electricity storage systems/facilities, including hydroelectric pumped storage, solar-thermal storage, batteries, flywheels, and compressed air systems. These systems typically use (or purchase) and store electricity that is generated during off-peak electricity demand periods (when electricity prices are relatively low), and they provide (or sell) the stored electricity during periods of high or peak electricity demand (when electricity prices are relatively high). Some facilities use electricity produced with intermittent renewable energy sources (wind and solar) when the renewable resource availability is high and provide the stored electricity when the renewable energy resource is low or unavailable. Nonhydro storage systems can also provide ancillary services to the electric power grid. Energy storage applications inherently use more electricity than they provide. Pumped-storage hydro systems use more electricity to pump water to water storage reservoirs than they produce with the stored water, and nonhydro storage systems have energy conversion and storage losses. Therefore electricity storage facilities have net negative electricity generation balances. Gross generation provides a better indicator about the activity level of storage technologies and is provided in the data releases of the EIA-923 Power Plant Operations Report.

Distributed generators are connected to the electricity grid, but they primarily supply some or all of the electricity demand of individual buildings or facilities. Sometimes, these systems may generate more electricity than the facility consumes, in which case the surplus electricity is sent to the grid. Most small-scale solar photovoltaic systems are distributed generators.

At the end of 2020, the United States had 1,117,475 MW-or about 1.12 billion kilowatts (kW)-of total utility-scale electricity generating capacity and about 27,724 MW-or nearly 0.03 billion kW-of small-scale solar photovoltaic electricity generating capacity.

Generating units fueled primarily with natural gas account for the largest share of utility-scale electricity generating capacity in the United States.

Energy sources for U.S. electricity generation

The mix of energy sources for U.S. electricity generation in the United States has changed over time, especially in recent years. Natural gas and renewable energy sources account for an increasing share of U.S. electricity generation, while coal-fired electricity generation has declined. In 1990, coal-fired power plants accounted for about 42% of total U.S. utility-scale electricity generating capacity and about 52% of total electricity generation. By the end of 2020, coal's share of electricity generating capacity was at 20% and coal accounted for 19% of total utility-scale electricity generation. During the same period, the share of natural gas-fired electricity generating capacity increased from 17% in 1990 to 43% in 2020, and its share of electricity generation more than tripled from 12% in 1990 to 40% in 2020.

Most U.S. nuclear and hydropower plants were built before 1990. Nuclear energy's share of total U.S. electricity generation has held steady at about 20% since 1990. Electricity generation from hydropower, historically the largest source of total annual utility-scale renewable electricity generation (until 2019), fluctuates from year to year because of precipitation patterns.

Total U.S. electricity generation from nonhydro renewables is increasing

Renewable electricity generation from sources other than hydropower has steadily increased in recent years, mainly because of additions to wind and solar generating capacity. Since 2014, total annual electricity generation from utility-scale nonhydro renewable sources has been greater than hydropower generation.

Wind energy's share of total utility-scale electricity generating capacity in the United States grew from 0.2% in 1990 to nearly 11% in 2020, and its share of total annual utility-scale electricity generation grew from less than 1% in 1990 to about 8% in 2020.

Although relatively small in terms of its share of total U.S. electricity capacity and generation, solar electricity generating capacity and generation have grown significantly in recent years. Utility-scale solar electricity generating capacity rose from about 314 MW-or 314,000 kW-in 1990 to about 47,848 MW (or about 48 million KW) at the end of 2020, of which about 96% was solar photovoltaic systems and 4% was solar thermal-electric systems. Solar energy's share of total U.S. utility-scale electricity generation in 2020 was about 2.3%, up from less than 0.1% in 1990. In addition, EIA estimates that at the end of 2020, there were 27,724 MW of small-scale solar photovoltaic generating capacity, and electricity generation from small-scale photovoltaic systems totaled was about 42 billion kWh.

Various factors influence the mix of energy sources for electricity generation

A decline in natural gas prices

State requirements to use more renewable energy sources

Availability of government and other financial incentives for building new renewable capacity

Federal air pollution emission regulations for power plants

Slowing electricity demand

Can be added in smaller increments to meet grid generating capacity requirements

Can respond more quickly to changes in hourly electricity demand

Generally have lower compliance costs with environmental regulations

Retail electricity sales

U.S. retail electricity sales to end-use customers totaled about 3,664 billion kWh-or 3.7 trillion kWh-in 2020, a decrease of about 147 billion kWh from 2019. Retail sales include net imports (imports minus exports) of electricity from Canada and Mexico.

Who sells electricity?

There are two general categories of electricity providers: full service providers, which sell bundled electricity services-energy (electricity) and delivery to end users, and other providers.

Full service providers may generate electricity from power plants that they own and sell the electricity to their customers and they may sell some of it to other types of providers. They may in turn purchase electricity from other full service providers or from independent power producers, which they sell to their customers. There are four general types of full service providers:

Investor owned utilities are electric utilities whose stock is publicly traded.

Public entities include municipalities, state power agencies, and municipal marketing authorities.

Federal entities are either owned or financed by the federal government.

Cooperatives are electric utilities owned by and operated for the benefit of the members of the cooperative.

Other providers market and sell electricity to the customers of full service providers or provide only electricity delivery services to consumers. They mostly include electricity marketers that operate in states where there is customer choice for selecting electricity providers. Full service providers deliver the electricity for the electricity marketers to consumers. There are also direct electricity transactions from independent power producers to (usually large) electricity consumers.

In addition to sales to end-use customers, electricity is also often traded on wholesale markets or through bilateral contracts.
Last updated: March 18, 2021

# data[].attributes.attachment_link.title
Electricity generation, capacity, and sales in the United States - U.S. Energy Information Administration (EIA)

# data[].attributes.attachment_link.description
Generation is a measure of electricity produced over time. Most electric power plants use some of the electricity they produce to operate the power plant. Capacity is the maximum level of electric power (electricity) that a power plant can supply at a specific point in time under certain conditions.

# data[].attributes.attachment_link.readable_text
Generation is a measure of electricity produced over time. Most electric power plants use some of the electricity they produce to operate the power plant.

Capacity is the maximum level of electric power (electricity) that a power plant can supply at a specific point in time under certain conditions.

Sales are the amount of electricity sold to customers over a period of time, and they account for most of U.S. electricity consumption.

More electricity is generated than sold, because some energy is lost (as heat) in transmission and distribution of electricity. In addition, some electricity consumers generate electricity and use most or all of it, and the amount they use is called direct use. These consumers include industrial, manufacturing, commercial, and institutional facilities, as well as homeowners who have their own electricity generators. The United States also exports and imports some electricity to and from Canada and Mexico. Total U.S. electricity consumption by end-use consumers is equal to U.S. retail sales of electricity plus direct use of electricity.

Utility scale includes electricity generation and capacity of generating units (generators) located at power plants with at least one megawatt (MW) of total electricity generating capacity.

Small scale includes generators with less than 1 MW of generating capacity that are usually at or near where the electricity is consumed. Most solar photovoltaic systems installed on building rooftops are small-scale systems.

Electricity generation

In 2020, net generation of electricity from utility-scale generators in the United States was about 4,009 billion kilowatthours (kWh) (or about 4 trillion kWh). EIA estimates that an additional 41.7 billion kWh (or about 0.04 trillion kWh) were generated with small-scale solar photovoltaic (PV) systems.

In 2020, about 60% of U.S. utility-scale electricity generation was produced from fossil fuels (coal, natural gas, and petroleum), about 20% was from nuclear energy, and about 20% was from renewable energy sources.

Electricity generating capacity

To ensure a steady supply of electricity to consumers, operators of the electric power system, or grid, call on electric power plants to produce and place the right amount of electricity on the grid at every moment to instantaneously meet and balance electricity demand.

Base load generating units normally supply all or part of the minimum, or base, demand (load) on the electric power grid. A base load generating unit runs continuously, producing electricity at a nearly constant rate throughout most of the day. Nuclear power plants generally operate as base load service, because of their low fuel costs and the technical limitations on load responsive operation. Geothermal and biomass units are also often operated in base load because of their low fuel costs. Many of the large hydro facilities, several coal plants, and an increasing number of natural gas-fired generators, particularly those in combined power applications, also supply base load power.

Peak load generating units help to meet electricity demand when demand is at its highest, or peak, such as in late afternoon and as when electricity use for air conditioning and heating increases during hot weather and cold weather respectively. These so-called peaking units are generally natural gas or petroleum fueled generators. In general, these generators are relatively inefficient and are costly to operate, but provide high- value service during peak demand periods. In some cases, pumped storage hydropower and conventional hydropower units also support grid operations by providing power during periods of peak demand.

Intermediate load generating units comprise the largest generating sector and provide load responsive operation between base load and peaking service. The demand profile varies over time and intermediate sources are in general technically and economically suited for following changes in load. Many energy sources and technologies are used in intermediate operation. Natural gas-fired combined cycle units, which currently provide more generation than any other technology, generally operate as intermediate sources.

Additional categories of electricity generators include

Intermittent renewable resource generators powered by wind and solar energy that generate electricity only when these resources are available (i.e., when it's windy or sunny). When these generators are operating, they tend to reduce the amount of electricity required from other generators to supply the electric power grid.

Electricity storage systems/facilities, including hydroelectric pumped storage, solar-thermal storage, batteries, flywheels, and compressed air systems. These systems typically use (or purchase) and store electricity that is generated during off-peak electricity demand periods (when electricity prices are relatively low), and they provide (or sell) the stored electricity during periods of high or peak electricity demand (when electricity prices are relatively high). Some facilities use electricity produced with intermittent renewable energy sources (wind and solar) when the renewable resource availability is high and provide the stored electricity when the renewable energy resource is low or unavailable. Nonhydro storage systems can also provide ancillary services to the electric power grid. Energy storage applications inherently use more electricity than they provide. Pumped-storage hydro systems use more electricity to pump water to water storage reservoirs than they produce with the stored water, and nonhydro storage systems have energy conversion and storage losses. Therefore electricity storage facilities have net negative electricity generation balances. Gross generation provides a better indicator about the activity level of storage technologies and is provided in the data releases of the EIA-923 Power Plant Operations Report.

Distributed generators are connected to the electricity grid, but they primarily supply some or all of the electricity demand of individual buildings or facilities. Sometimes, these systems may generate more electricity than the facility consumes, in which case the surplus electricity is sent to the grid. Most small-scale solar photovoltaic systems are distributed generators.

At the end of 2020, the United States had 1,117,475 MW-or about 1.12 billion kilowatts (kW)-of total utility-scale electricity generating capacity and about 27,724 MW-or nearly 0.03 billion kW-of small-scale solar photovoltaic electricity generating capacity.

Generating units fueled primarily with natural gas account for the largest share of utility-scale electricity generating capacity in the United States.

Energy sources for U.S. electricity generation

The mix of energy sources for U.S. electricity generation in the United States has changed over time, especially in recent years. Natural gas and renewable energy sources account for an increasing share of U.S. electricity generation, while coal-fired electricity generation has declined. In 1990, coal-fired power plants accounted for about 42% of total U.S. utility-scale electricity generating capacity and about 52% of total electricity generation. By the end of 2020, coal's share of electricity generating capacity was at 20% and coal accounted for 19% of total utility-scale electricity generation. During the same period, the share of natural gas-fired electricity generating capacity increased from 17% in 1990 to 43% in 2020, and its share of electricity generation more than tripled from 12% in 1990 to 40% in 2020.

Most U.S. nuclear and hydropower plants were built before 1990. Nuclear energy's share of total U.S. electricity generation has held steady at about 20% since 1990. Electricity generation from hydropower, historically the largest source of total annual utility-scale renewable electricity generation (until 2019), fluctuates from year to year because of precipitation patterns.

Total U.S. electricity generation from nonhydro renewables is increasing

Renewable electricity generation from sources other than hydropower has steadily increased in recent years, mainly because of additions to wind and solar generating capacity. Since 2014, total annual electricity generation from utility-scale nonhydro renewable sources has been greater than hydropower generation.

Wind energy's share of total utility-scale electricity generating capacity in the United States grew from 0.2% in 1990 to nearly 11% in 2020, and its share of total annual utility-scale electricity generation grew from less than 1% in 1990 to about 8% in 2020.

Although relatively small in terms of its share of total U.S. electricity capacity and generation, solar electricity generating capacity and generation have grown significantly in recent years. Utility-scale solar electricity generating capacity rose from about 314 MW-or 314,000 kW-in 1990 to about 47,848 MW (or about 48 million KW) at the end of 2020, of which about 96% was solar photovoltaic systems and 4% was solar thermal-electric systems. Solar energy's share of total U.S. utility-scale electricity generation in 2020 was about 2.3%, up from less than 0.1% in 1990. In addition, EIA estimates that at the end of 2020, there were 27,724 MW of small-scale solar photovoltaic generating capacity, and electricity generation from small-scale photovoltaic systems totaled was about 42 billion kWh.

Various factors influence the mix of energy sources for electricity generation

A decline in natural gas prices

State requirements to use more renewable energy sources

Availability of government and other financial incentives for building new renewable capacity

Federal air pollution emission regulations for power plants

Slowing electricity demand

Can be added in smaller increments to meet grid generating capacity requirements

Can respond more quickly to changes in hourly electricity demand

Generally have lower compliance costs with environmental regulations

Retail electricity sales

U.S. retail electricity sales to end-use customers totaled about 3,664 billion kWh-or 3.7 trillion kWh-in 2020, a decrease of about 147 billion kWh from 2019. Retail sales include net imports (imports minus exports) of electricity from Canada and Mexico.

Who sells electricity?

There are two general categories of electricity providers: full service providers, which sell bundled electricity services-energy (electricity) and delivery to end users, and other providers.

Full service providers may generate electricity from power plants that they own and sell the electricity to their customers and they may sell some of it to other types of providers. They may in turn purchase electricity from other full service providers or from independent power producers, which they sell to their customers. There are four general types of full service providers:

Investor owned utilities are electric utilities whose stock is publicly traded.

Public entities include municipalities, state power agencies, and municipal marketing authorities.

Federal entities are either owned or financed by the federal government.

Cooperatives are electric utilities owned by and operated for the benefit of the members of the cooperative.

Other providers market and sell electricity to the customers of full service providers or provide only electricity delivery services to consumers. They mostly include electricity marketers that operate in states where there is customer choice for selecting electricity providers. Full service providers deliver the electricity for the electricity marketers to consumers. There are also direct electricity transactions from independent power producers to (usually large) electricity consumers.

In addition to sales to end-use customers, electricity is also often traded on wholesale markets or through bilateral contracts.
Last updated: March 18, 2021

# data[].attributes.attachment_link.title
Electricity generation, capacity, and sales in the United States - U.S. Energy Information Administration (EIA)

# data[].attributes.attachment_link.description
Generation is a measure of electricity produced over time. Most electric power plants use some of the electricity they produce to operate the power plant. Capacity is the maximum level of electric power (electricity) that a power plant can supply at a specific point in time under certain conditions.

# data[].attributes.attachment_link.readable_text
Describe coal and its processing.

List the products of coal burning that promotes pollution.

Coal is a complex solid material derived primarily from plants that died and were buried hundreds of millions of years ago and were subsequently subjected to high temperatures and pressures. It is a combustible black or brownish-black sedimentary rock with a high amount of carbon and hydrocarbons. Coal is classified into four main types, or ranks depending on the types and amounts of carbon present and on the amount of heat energy the coal can produce, including anthracite, bituminous, subbituminous, and lignite (highest to lowest ranked, pictured in Figure \(\PageIndex{1}\).

Figure \(\PageIndex{1}\) Different types of coal. Images obtained from Wikimedia Commons.

There are four distinct classes of coal (Table \(\PageIndex{1}\)); their hydrogen and oxygen contents depend on the length of time the coal has been buried and the pressures and temperatures to which it has been subjected. The most abundant form in the United States is bituminous coal, which has a high sulfur content becauseof the presence of small particles of pyrite (FeS ₂). The combustion of coal releases the sulfur in FeS ₂ as SO ₂, which is a major contributor to acid rain.

Type

% Carbon

Hydrogen:Carbon Mole Ratio

% Oxygen

% Sulfur

US Deposits

Peat, a precursor to coal, is the partially decayed remains of plants that grow in swampy areas. It is removed from the ground in the form of soggy bricks of mud that will not burn until they have been dried. If a peat bog were buried under many layers of sediment for a few million years, the peat could eventually be compressed and heated enough to become lignite, the lowest grade of coal; given enough time and heat, lignite would eventually become anthracite, a much better fuel.

For us to use the potential energy stored in coal, it first must be mined from the ground. This process in itself uses a great deal of resources and has its own environmental impacts. Coal then typically undergoes processing to make it suitable for use in coal-fire power plants. Finally, the processed coal is burned in these power plants, and the kinetic energy released from its combustion is harnessed for electricity generation or other purposes. Figure \(\PageIndex{2}\) below is a schematic diagram showing a typical layout of a coal-fire power plant. You can also watch a short video of a virtual tour of a coal power plant at the URL provided below.

Power Plant Virtual Tour
Video \(\PageIndex{1}\) Coal-Fueled Power Plant Virtual Tour Video

Figure \(\PageIndex{2}\)Diagram of a typical steam-cycle coal power plant (proceeding from left to right). Image by US Tennessee Valley Authority - Public domain. www.tva.com

The Global Carbon Cycle

Figure \(\PageIndex{3}\) illustrates the global carbon cycle, the distribution and flow of carbon on Earth. Normally, the fate of atmospheric CO ₂ is to either (1) dissolve in the oceans and eventually precipitate as carbonate rocks or (2) be taken up by plants. The rate of uptake of CO ₂ by the ocean is limited by its surface area and the rate at which gases dissolve, which are approximately constant. The rate of uptake of CO ₂ by plants, representing about 60 billion metric tons of carbon per year, partly depends on how much of Earth's surface is covered by vegetation. Unfortunately, the rapid deforestation for agriculture is reducing the overall amount of vegetation, and about 60 billion metric tons of carbon are released annually as CO ₂ from animal respiration and plant decay. The amount of carbon released as CO ₂ every year by fossil fuel combustion is estimated to be about 5.5 billion metric tons. The net result is a system that is slightly out of balance, experiencing a slow but steady increase in atmospheric CO ₂ levels. As a result, average CO ₂ levels have increased by about 30% since 1850.

Figure \(\PageIndex{3}\) The global carbon cycle.

Most of Earth's carbon is found in the crust, where it is stored as calcium and magnesium carbonate in sedimentary rocks. The oceans also contain a large reservoir of carbon, primarily as the bicarbonate ion (HCO ₃−). Green plants consume about 60 billion metric tons of carbon per year as CO ₂ during photosynthesis, and about the same amount of carbon is released as CO ₂ annually from animal and plant respiration and decay. The combustion of fossil fuels releases about 5.5 billion metric tons of carbon per year as CO ₂.

Pollution from Coal Burning

In the United States and most of the world, most of the coal consumed is used as a fuel to generate electricity. Burning coal produces emissions such as sulfur dioxide (SO ₂) and nitrogen oxides (NO x) that are associated with acid rain (more on this in chapter 6). Carbon dioxide (CO ₂), another emission resulting from burning coal, is a major greenhouse gas that is associated with global warming (see Chapter 13 ). Burning of coal is classified as incomplete combustion, since the reaction of carbon (in coal) with oxygen produces carbon monoxide and/or carbon (soot) in addition to carbon dioxide.

Burning coal produces emissions that also impact human health. Emissions such as sulfur dioxide (SO ₂), nitrogen oxides (NO x) and particulates contribute to respiratory illnesses. Particulates also contribute to a condition among coal miners and other coal workers known as coal workers' pneumoconiosis (CWP) or black lung disease, which results from long exposure to coal dust. Inhaled coal dust progressively builds up in the lungs and is unable to be removed by the body; this leads to inflammation, fibrosis, and in worse cases, tissue death (necrosis).

Coal is the largest source of mercury and also a source of other heavy metals, many of which have been linked to both neurological and developmental problems in humans and other animals. Mercury concentrations in the air usually are low and of little direct concern. However, when mercury enters water, either directly or through deposition from the air, biological processes transform it into methylmercury, a highly toxic chemical that accumulates in fish and the animals (including humans) that eat fish.

Reducing the Environmental Impacts of Coal Use

Regulations such as the Clean Air Act and the Clean Water Act require industries to reduce pollutants released into the air and water. Below are some actions that have been taken to reduce the negative impacts of coal on human and environmental health:

* Clean coal technology: Industry has found several ways to reduce sulfur, NO x, and other impurities from coal before burning.

* Coal consumers have shifted toward greater use of low sulfur coal.

* Power plants use scrubbers, to clean SO ₂, NO x, particulate matter, and mercury from the smoke before it leaves their smokestacks. In addition, industry and the U.S. government have cooperated to develop technologies that make coal more energy-efficient so less needs to be burned.

* Research is underway to address emissions of carbon dioxide from coal combustion. Carbon capture & sequestration separates CO ₂ from emissions sources and recovers it in a concentrated stream. The CO ₂ can then be sequestered, which puts CO ₂ into storage, possibly underground, where it will remain permanently.

* Reuse and recycling can also reduce coal's environmental impact. Land that was previously used for coal mining can be reclaimed and used for airports, landfills, and golf courses. Waste products captured by scrubbers can be used to produce products like cement and synthetic gypsum for wallboard.

Summary

Coal is a complex solid material derived primarily from plants that died and were buried hundreds of millions of years ago and were subsequently subjected to high temperatures and pressures.

Coal is classified into four main types, depending on the types and amounts of carbon present and on the amount of heat energy the coal can produce, including anthracite, bituminous, subbituminous, and lignite.

The processing of coal is described as well as the environmental and health impacts of its use.

Research is underway and various approaches are implemented (clean coal technology, use of low sulfur coal, use of scrubbers etc.) to reduce the environmental impacts of coal use.

Contributors and Attributions

Libretext: Introduction to Environmental Science (Zendher et al.)

Libretext: General Chemistry (Petrucci et al.)

Anne Marie Helmenstine, Ph.D. "What Is a Combustion Reaction?" ThoughtCo, www.thoughtco.com/combustion-reactions-604030.

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Describe coal and its processing. List the products of coal burning that promotes pollution. Coal is a complex solid material derived primarily from plants that died and were buried hundreds of millions of years ago and were subsequently subjected to high temperatures and pressures.

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The power of a steam engine does not lie in its cylinders, beam, shatt, and levers ; no, these only apply the power usefully. The force that moves the engine is steam, and that which produces steam is a, chemical action the combustion of fuel. Combustion appears to be-a very simple operation, but we…

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Natural gas has many qualities that make it an efficient, relatively clean burning, and economical energy source. However, the production and use of natural gas have some environmental and safety issues to consider.

Natural gas is a relatively clean burning fossil fuel

Burning natural gas for energy results in fewer emissions of nearly all types of air pollutants and carbon dioxide (CO2) than burning coal or petroleum products to produce an equal amount of energy. About 117 pounds of carbon dioxide are produced per million British thermal units (MMBtu) equivalent of natural gas compared with more than 200 pounds of CO2 per MMBtu of coal and more than 160 pounds per MMBtu of distillate fuel oil. The clean burning properties of natural gas have contributed to increased natural gas use for electricity generation and as a transportation fuel for fleet vehicles in the United States.

Natural gas is mainly methane-a strong greenhouse gas

Some natural gas leaks into the atmosphere from oil and natural gas wells, storage tanks, pipelines, and processing plants. The U.S. Environmental Protection Agency estimates that in 2018, methane emissions from natural gas and petroleum systems and from abandoned oil and natural gas wells were the source of about 29% of total U.S. methane emissions and about 3% of total U.S. greenhouse gas emissions ¹. The oil and natural gas industry takes steps to prevent natural gas leaks.

Natural gas exploration, drilling, and production affects the environment

When geologists explore for natural gas deposits on land, they may disturb vegetation and soil with their vehicles. Drilling a natural gas well on land may require clearing and leveling an area around the well site. Well drilling activities produce air pollution and may disturb people, wildlife, and water resources. Laying pipelines that transport natural gas from wells usually requires clearing land to bury the pipe. Natural gas production can also produce large volumes of contaminated water. This water requires proper handling, storage, and treatment so that it does not pollute land and other waters. Natural gas wells and pipelines often have engines to run equipment and compressors, which produce air pollutants and noise.

In areas where natural gas is produced at oil wells but is not economical to transport for sale or contains high concentrations of hydrogen sulfide (a toxic gas), it is burned (flared) at well sites. Natural gas flaring produces CO2, carbon monoxide, sulfur dioxide, nitrogen oxides, and many other compounds, depending on the chemical composition of the natural gas and on how well the natural gas burns in the flare. However, flaring is safer than releasing natural gas into the air and results in lower overall greenhouse gas emissions because CO2 is not as strong a greenhouse gas as methane.

Natural gas well drilling operation

Source: Bureau of Land Management (public domain)

Advances in drilling and production technologies have positive and negative effects on the environment

New drilling and natural gas recovery technologies significantly reduce the land area that is disturbed to develop oil and gas resources. Horizontal and directional drilling techniques make it possible to produce more natural gas from a single well than in the past, so fewer wells are necessary to develop a natural gas field.

The fracturing of wells requires large amounts of water. In some areas of the country, significant use of water for fracking may affect aquatic habitats and the availability of water for other uses.

If mismanaged, hydraulic fracturing fluid-which may contain potentially hazardous chemicals-could be released through spills, leaks, faulty well construction, or other exposure pathways. These releases could contaminate surrounding areas.

Hydraulic fracturing produces large amounts of wastewater at the surface, which may contain dissolved chemicals and other contaminants that require treatment before disposal or reuse. Because of the quantities of water produced and the complexities inherent in treating some of the wastewater components, proper treatment and disposal of the wastewater is important.

According to the U.S. Geological Survey, hydraulic fracturing "...causes small earthquakes, but they are almost always too small to be a safety concern. In addition to natural gas, fracking fluids and formation waters are returned to the surface. These wastewaters are frequently disposed of by injection into deep wells. The injection of wastewater into the subsurface can cause earthquakes that are large enough to be felt and may cause damage."

Natural gas could be released to the atmosphere during and after well drilling, and the amount of these releases are under investigation.

Natural gas production, transportation, distribution, and storage require strict safety regulations and standards

Because a natural gas leak could cause an explosion, strict government regulations and industry standards are in place to ensure the safe transportation, storage, distribution, and use of natural gas. Because processed natural gas has no odor, natural gas companies add a strong, rotten egg-like smelling substance called mercaptan to natural gas so that people can smell leaks.
Last updated: September 24, 2020

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Natural gas and the environment - U.S. Energy Information Administration (EIA)

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Natural gas has many qualities that make it an efficient, relatively clean burning, and economical energy source. However, the production and use of natural gas have some environmental and safety issues to consider. Burning natural gas for energy results in fewer emissions of nearly all types of air pollutants and carbon dioxide (CO2) than burning coal or petroleum products to produce an equal amount of energy.

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What is natural gas?

Natural gas is a fossil fuel energy source. Natural gas contains many different compounds. The largest component of natural gas is methane, a compound with one carbon atom and four hydrogen atoms (CH ₄). Natural gas also contains smaller amounts of natural gas liquids (NGLs, which are also hydrocarbon gas liquids), and nonhydrocarbon gases, such as carbon dioxide and water vapor. We use natural gas as a fuel and to make materials and chemicals.

How did natural gas form?

Millions to hundreds of millions of years ago, the remains of plants and animals (such as diatoms) built up in thick layers on the earth's surface and ocean floors, sometimes mixed with sand, silt, and calcium carbonate. Over time, these layers were buried under sand, silt, and rock. Pressure and heat changed some of this carbon and hydrogen-rich material into coal, some into oil (petroleum), and some into natural gas.

Where is natural gas found?

In some places, natural gas moved into large cracks and spaces between layers of overlying rock. The natural gas found in these types of formations is sometimes called conventional natural gas. In other places, natural gas occurs in the tiny pores (spaces) within some formations of shale, sandstone, and other types of sedimentary rock. This natural gas is referred to as shale gas or tight gas, and it is sometimes called unconventional natural gas. Natural gas also occurs with deposits of crude oil, and this natural gas is called associated natural gas. Natural gas deposits are found on land, and some are offshore and deep under the ocean floor. Natural gas found in coal deposits is called coalbed methane.
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How do we find natural gas?

The search for natural gas begins with geologists who study the structure and processes of the earth. They locate the types of geologic formations that are likely to contain natural gas deposits.

Geologists often use seismic surveys on land and in the ocean to find the right places to drill natural gas and oil wells. Seismic surveys create and measure seismic waves in the earth to get information on the geology of rock formations. Seismic surveys on land may use a thumper truck, which has a vibrating pad that pounds the ground to create seismic waves in the underlying rock. Sometimes, small amounts of explosives are used. Seismic surveys conducted in the ocean use blasts of sound that create sonic waves to explore the geology beneath the ocean floor.

If the results of seismic surveys indicate that a site has potential for producing natural gas, an exploratory well is drilled and tested. The results of the test provide information on the quality and quantity of natural gas available in the resource.

What happens when natural gas is found?

If the results from a test well show that a geologic formation has enough natural gas to make a profit, one or more production (or development) wells are drilled. Natural gas wells can be drilled vertically and horizontally into natural gas-bearing formations. In conventional natural gas deposits, the natural gas generally flows easily up through wells to the surface.

In the United States and in a few other countries, natural gas is produced from shale and other types of sedimentary rock formations by forcing water, chemicals, and sand down a well under high pressure. This process, called hydraulic fracturing or fracking (sometimes referred to as unconventional production), breaks up the formation, releases the natural gas from the rock, and allows the natural gas to flow to and up wells to the surface. At the top of the well, natural gas is collected in gathering pipelines and sent to natural gas processing plants.

Natural gas is processed for sale and consumption

Natural gas withdrawn from natural gas or crude oil wells is called wet natural gas because, along with methane, it usually contains NGLs-ethane, propane, butanes, and pentanes-and water vapor. Wellhead natural gas may also contain nonhydrocarbons such as sulfur, helium, nitrogen, hydrogen sulfide, and carbon dioxide, most of which must be removed from natural gas before it is sold to consumers.

From the wellhead, natural gas is sent to processing plants where water vapor and nonhydrocarbon compounds are removed and NGLs are separated from the wet gas and sold separately. Some ethane is often left in the processed natural gas. The separated NGLs are called natural gas plant liquids (NGPLs), and the processed natural gas is called dry, consumer-grade, or pipeline-quality natural gas. Some wellhead natural gas is sufficiently dry and satisfies pipeline transportation standards without processing. Chemicals called odorants are added to natural gas so that leaks in natural gas pipelines can be detected. Dry natural gas is sent through pipelines to underground storage fields or to distribution companies and then to consumers.

In places where natural gas pipelines are not available to take away the associated natural gas produced from oil wells, the natural gas may be reinjected into the oil-bearing formation, or it may be vented or burned (flared). Reinjecting unmarketable natural gas can help to maintain pressure in oil wells to improve oil production.

Coalbed methane can be extracted from coal deposits before or during coal mining, and it can be added to natural gas pipelines without any special treatment.

Most of the natural gas consumed in the United States is produced in the United States. Some natural gas is imported from Canada and Mexico in pipelines. A small amount of natural gas is also imported as liquefied natural gas.
Last updated: December 27, 2022

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Where and how natural gas is found and produced including by hydraulic fracturing (fracking) in shale and other geologic formations.

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Nuclear power comes from nuclear fission

Nuclear power plants heat water to produce steam. The steam is used to spin large turbines that generate electricity. Nuclear power plants use heat produced during nuclear fission to heat water.

In nuclear fission, atoms are split apart to form smaller atoms, releasing energy. Fission takes place inside the reactor of a nuclear power plant. At the center of the reactor is the core, which contains uranium fuel.

The uranium fuel is formed into ceramic pellets. Each ceramic pellet produces about the same amount of energy as 150 gallons of oil. These energy-rich pellets are stacked end-to-end in 12-foot metal fuel rods. A bundle of fuel rods, some with hundreds of rods, is called a fuel assembly. A reactor core contains many fuel assemblies.

The heat produced during nuclear fission in the reactor core is used to boil water into steam, which turns the blades of a steam turbine. As the turbine blades turn, they drive generators that make electricity. Nuclear plants cool the steam back into water in a separate structure at the power plant called a cooling tower, or they use water from ponds, rivers, or the ocean. The cooled water is then reused to produce steam.

Containment dome of a nuclear reactor

Source: Stock photography (copyrighted)

Nuclear power plants have generated about 20% of U.S. electricity since 1990

As of December 31, 2020, 94 nuclear reactors were operating at 56 nuclear power plants in 28 states. Thirty-two of the plants have two reactors, and three plants have three reactors. Nuclear power plants have supplied about 20% of total annual U.S. electricity since 1990. Learn more about the U.S. nuclear energy industry.

The United States generates more nuclear power than any other country

In 2019, 31 countries had commercial nuclear power plants, and in 14 of the countries, nuclear energy supplied at least 20% of their total annual electricity generation. The United States had the largest nuclear electricity generation capacity and generated more nuclear electricity than any other country. France, with the second-largest nuclear electricity generation capacity and second-highest nuclear electricity generation, had the largest share-about 70%-of total annual electricity generation from nuclear energy.

Top five nuclear electricity generation countries, 2019
Last updated: April 6, 2021

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Nuclear power plants - U.S. Energy Information Administration (EIA)

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Nuclear power plants heat water to produce steam. The steam is used to spin large turbines that generate electricity. Nuclear power plants use heat produced during nuclear fission to heat water. In nuclear fission, atoms are split apart to form smaller atoms, releasing energy. Fission takes place inside the reactor of a nuclear power plant.

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The nuclear fuel cycle consists of two phases: the front end and the back end. Front-end steps prepare uranium for use in nuclear reactors. Back-end steps ensure that used-or spent -but still highly radioactive, nuclear fuel is safely managed, prepared, and disposed of.

Nuclear power plants primarily use a specific type of uranium (U-235) for nuclear fission because its atoms are easily split apart. Although uranium is about 100 times more common than silver, U-235 is relatively rare, at just over 0.7% of natural uranium. The U-235 is separated from uranium ore at uranium mills or from a slurry at in-situ leaching facilities to produce uranium concentrate, which can be used as a fuel. The uranium concentrate is first processed in conversion and enrichment facilities to increase the level of U-235 in the uranium to 3%-5%, and then in reactor fuel fabrication plants, where it is made into reactor fuel pellets and fuel rods.

Nuclear fuel is loaded into reactors and used until the fuel assemblies become highly radioactive and must be removed for temporary storage and eventual disposal. Spent fuel material could be processed to recover any remaining uranium that could undergo fission again in a new fuel assembly (spent fuel reprocessing), but it is not permitted in the United States.

The front end of the nuclear fuel cycle

Exploration

The nuclear fuel cycle starts with exploring for uranium and developing mines to extract uranium ore. A variety of techniques are used to locate uranium, such as airborne radiometric surveys, chemical sampling of groundwater and soils, and exploratory drilling to understand the underlying geology. Once uranium ore deposits are located, the mine developer usually follows up with more closely spaced in fill, or development drilling, to determine how much uranium is available and what it might cost to recover it.

Uranium mining

Underground mining

Open pit mining

In-place (in-situ) solution mining

Heap leaching

Before 1980, most U.S. uranium was produced using open pit and underground mining techniques. Today, most U.S. uranium is produced using a solution mining technique commonly called in-situ-leach (ISL) or in-situ-recovery (ISR) mining. This process extracts the uranium that coats the sand and gravel particles of groundwater reservoirs. The sand and gravel particles are exposed to a solution with a pH that has been elevated slightly by using oxygen, carbon dioxide, or caustic soda. The uranium dissolves into the groundwater, which is pumped out of the reservoir and processed at a uranium mill. Another similar process, heap leaching, involves spraying an acidic liquid solution onto piles of crushed uranium ore. The solution drains down through the crushed ore and leaches uranium out of the rock, which is recovered from underneath the pile. Heap leaching is no longer used in the United States.

Uranium milling

After the uranium ore is extracted from an open pit or underground mine, it is refined into uranium concentrate at a uranium mill. The ore is crushed, pulverized, and ground into a fine powder. Chemicals are added to the fine powder, which causes a reaction that separates the uranium from the other minerals. Groundwater from solution mining operations is circulated through a resin bed to extract and concentrate the uranium.

Despite the name, the concentrated uranium product is typically a black or brown substance called yellowcake (U ₃O ₈). Mined uranium ore typically yields one to four pounds of U ₃O ₈ per ton of ore, or 0.05% to 0.20% yellowcake. The solid waste material from pit and underground mining operations is called mill tailings. The processed water from solution mining is returned to the groundwater reservoir where the mining process is repeated.

Uranium conversion

The next step in the nuclear fuel cycle is to convert yellowcake into uranium hexafluoride (UF ₆) gas at a converter facility. Three forms (isotopes) of uranium occur naturally: U-234, U-235, and U-238. Current U.S. nuclear reactor designs require a stronger concentration (enrichment) of the U-235 isotope to operate efficiently. The uranium hexafluoride gas produced in the converter facility is called natural UF ₆ because the original concentrations of uranium isotopes are unchanged.

Uranium enrichment

After conversion, the UF ₆ gas is sent to an enrichment plant where the individual uranium isotopes are separated to produce enriched UF ₆, which has a 3% to 5% concentration of U-235.

Two types of uranium enrichment processes have been used in the United States: gaseous diffusion and gas centrifuge. The United States has one operating enrichment plant, and it uses a gas centrifuge process. Enriched UF ₆ is sealed in canisters and allowed to cool and solidify before it is transported to a nuclear reactor fuel assembly plant by train, truck, or barge.

Atomic vapor laser isotope separation (AVLIS) and molecular laser isotope separation (MLIS) are new enrichment technologies under development. These laser-based enrichment processes can achieve higher initial enrichment (isotope separation) factors than the diffusion or centrifuge processes and can produce enriched uranium more quickly than other techniques.

Uranium reconversion and nuclear fuel fabrication

Once the uranium is enriched, it is ready to be converted into nuclear fuel. At a nuclear fuel fabrication facility, the UF ₆, in solid form, is heated to gaseous form, and then the UF ₆ gas is chemically processed to form uranium dioxide (UO ₂) powder. The powder is then compressed and formed into small ceramic fuel pellets. The pellets are stacked and sealed into long metal tubes that are about 1 centimeter in diameter to form fuel rods. The fuel rods are then bundled together to make up a fuel assembly. Depending on the reactor type, each fuel assembly has 179 to 264 fuel rods. A typical reactor core holds 121 to 193 fuel assemblies.

At the reactor

Once the fuel assemblies are fabricated, trucks transport them to the reactor sites. The fuel assemblies are stored onsite in fresh fuel storage bins until the reactor operators need them. At this stage, the uranium is only mildly radioactive, and essentially all radiation is contained within the metal tubes. Typically, reactor operators change out about one-third of the reactor core (40 to 90 fuel assemblies) every 12 to 24 months.

The reactor core is a cylindrical arrangement of the fuel bundles that is about 12 feet in diameter and 14 feet tall and encased in a steel pressure vessel with walls that are several inches thick. The reactor core has essentially no moving parts except for a small number of control rods that are inserted to regulate the nuclear fission reaction. Placing the fuel assemblies next to each other and adding water initiates the nuclear reaction.

A nuclear fuel assembly

The back end of the nuclear fuel cycle

Interim storage and final disposal in the United States

After use in the reactor, fuel assemblies become highly radioactive and must be removed and submerged in a pool of water for several years at the reactor site. Although the fission reaction has stopped, the spent fuel continues to give off heat from the decay of the radioactive elements that were created when the uranium atoms were split apart. The water in the spent fuel pool serves to both cool the fuel and block the release of radiation. From 1968 through December 31, 2017, a total of 276,879 fuel assemblies had been discharged and stored at the sites of 119 closed and operating commercial nuclear reactors in the United States.

Within a few years, the spent fuel cools in the pool and may be moved to a dry cask storage container at the power plant site. Many reactor operators store their older, spent fuel in these special air-conditioned concrete or steel containers.

The final step in the nuclear fuel cycle is to collect the spent fuel assemblies from the interim storage sites for final disposition in a permanent underground repository. The United States currently has no permanent underground repository for high-level nuclear waste.
Last updated: October 26, 2023.

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The nuclear fuel cycle - U.S. Energy Information Administration (EIA)

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The nuclear fuel cycle including uranium mines, uranium mills, nuclear fuel fabrication, and nuclear waste storage and disposal.

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What is crude oil and what are petroleum products?

We call crude oil and petroleum fossil fuels because they are mixtures of hydrocarbons that formed from the remains of animals and plants (diatoms) that lived millions of years ago in a marine environment before the existence of dinosaurs. Over millions of years, the remains of these animals and plants were covered by layers of sand, silt, and rock. Heat and pressure from these layers turned the remains into what we now call crude oil or petroleum. The word petroleum means rock oil or oil from the earth.
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Crude oil and other hydrocarbons exist in liquid or gaseous form in underground pools or reservoirs, in tiny spaces within sedimentary rocks, and near the earth's surface in tar (or oil) sands. Petroleum products are fuels made from crude oil and hydrocarbons contained in natural gas. Petroleum products can also be made from coal, natural gas, and biomass.

Products made from crude oil

After crude oil is removed from the ground, it is sent to a refinery where different parts of the crude oil are separated into useable petroleum products. These petroleum products include gasoline, distillates such as diesel fuel and heating oil, jet fuel, petrochemical feedstocks, waxes, lubricating oils, and asphalt. Learn more in Refining crude oil-inputs and outputs

A U.S. 42-gallon barrel of crude oil yields about 45 gallons of petroleum products in U.S. refineries because of refinery processing gain. This increase in volume is similar to what happens to popcorn when it is popped. A corn kernel is smaller and more dense than a popped kernel. The amount of individual products produced varies from month-to-month and year-to-year as refineries adjust production to meet market demand and to maximize profitability.
Last updated: April 19, 2022, with most recent data avaiable at the time of update; data are preliminary

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We call crude oil and petroleum fossil fuels because they are mixtures of hydrocarbons that formed from the remains of animals and plants (diatoms) that lived millions of years ago in a marine environment before the existence of dinosaurs. Over millions of years, the remains of these animals and plants were covered by layers of sand, silt, and rock.

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Crude oil and other liquids produced from fossil fuels are refined into petroleum products that people use for many different purposes. Biofuels are also used as petroleum products, mostly in mixtures with gasoline and diesel fuel.

Petroleum has historically been the most-consumed energy source in terms of total annual U.S. energy consumption. We use petroleum products to propel vehicles, to heat buildings, and to produce electricity. In the industrial sector, the petrochemical industry uses petroleum as a raw material (a feedstock) to make products such as plastics, polyurethane, solvents, and hundreds of other intermediate and end-user goods.

In 2022, U.S. total petroleum consumption averaged about 20.28 million barrels per day (b/d), which included about 1.17 million b/d of biofuels (1.002 b/d of fuel ethanol and 0.164 b/d of biodiesel, renewable diesel, and other biofuels combined). ¹ U.S. total petroleum consumption was about 2% higher in 2022 than in 2021 and about 12% higher than in 2020, largely because the U.S. economy was returning to pre-COVID-19 pandemic activity levels. Consumption of nearly all petroleum products in 2022 was higher than in 2021.

What petroleum products do people consume most?

Gasoline is the most-consumed petroleum product in the United States. In 2022, consumption of finished motor gasoline averaged about 8.78 million b/d (369 million gallons per day), which was about 43% of total U.S. petroleum consumption. Finished motor gasoline includes fuel ethanol.

Distillate fuel oil is the second-most-consumed petroleum product in the United States. Distillate fuel oil includes diesel fuel and heating oil. Diesel fuel is used in diesel engines, which are often in heavy construction equipment, trucks, buses, tractors, boats, trains, some automobiles, and electricity generators. Heating oil, also called fuel oil, is used for heating homes and buildings in boilers and furnaces, for industrial heating, and for producing electricity in power plants. In 2022, total distillate fuel oil consumption averaged about 3.96 million b/d (166 million gallons per day), which was 20% of total U.S. petroleum consumption.

Hydrocarbon gas liquids (HGLs), the third-most-used category of petroleum in the United States, include propane, ethane, butane, and other HGLs that are produced at natural gas processing plants and oil refineries. HGLs have many uses. Total consumption of HGLs in 2022 averaged about 3.59 million b/d, accounting for about 18% of total petroleum consumption.

Jet fuel is the fourth-most-used petroleum product in the United States. Jet fuel consumption averaged about 1.56 million b/d (65 million gallons per day) in 2022, accounting for about 8% of total petroleum consumption.

Product

Annual consumption (million barrels per day)

Data source: U.S. Energy Information Administration, Petroleum and Other Liquids-Product Supplied, as of June 2023
Note: Sum of individual products may not equal total because of independent rounding. Finished motor gasoline includes fuel ethanol. Biofuels includes biodiesel, renewable diesel, and other biofuels. Miscellaneous other products includes all finished petroleum products not classified elsewhere, including petrolatum, lube refining byproducts (aromatic extracts and tars), absorption oils, ram-jet fuel, petroleum rocket fuels, synthetic natural gas feedstocks, and specialty oils.

How much petroleum does the world consume?

In 2021, total world petroleum consumption was about 97.26 million b/d.

What is the outlook for U.S. petroleum consumption?

In the Annual Energy Outlook 2023 Reference case, the U.S. Energy Information Administration projects U.S. total consumption of petroleum and other liquids in 2050 to be nearly equal to the projection for 2023. Petroleum and other liquid fuels will decline from about 37% of total U.S. energy consumption in 2023 to about 34% of total annual U.S. energy consumption in 2050.

Also in the Reference case, liquid fuels continue as the main energy source for the transportation sector, but transportation sector liquid fuels consumption on an energy-content basis is projected to be about 10% lower in 2050 than in 2023.
Last updated: August 22, 2023, with data available from source reports as indicated; data for 2022 are preliminary.

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Use of oil - U.S. Energy Information Administration (EIA)

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The types and amounts of petroleum products consumed annually in the United States, and a list of the top 5 gasoline consuming states.

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Petroleum is a broad term that groups together a combination of organic liquids and gases that is formed after kerogen is heated and compressed over long periods of time. This mix can be fairly complex, but the main gaseous component of petroleum is natural gas - largely methane - whereas the main liquid component is crude oil. Crude oil itself is a complex mixture of hydrocarbons, so the exact composition of petroleum is never the same. Secondary fuels such as gasoline, kerosene, heating oil, and diesel fuel are all included in the definition of "petroleum". Petroleum traps energy, first originating from the Sun, that was captured by photosynthetic plankton in ancient oceans. Just like coal, petroleum is a type of fossil fuel.

The formation of petroleum occurred hundreds of millions of years ago during a period known as the Carboniferous period. During this time period, dead organic material accumulated and was decomposed by bacteria. Sediment - mostly mud and sand - then covered this material, creating high temperature and pressure conditions resulting in the creation of hydrocarbon molecules. The resulting materials were either liquid, gaseous, or solid. For more specific explanations of the formation of different components of petroleum, see the formation of oil or the formation of natural gas. Petroleum exists in many sedimentary rock formations, and because of its fluid nature it is able to migrate through stone and collect in porous rocks. If this petroleum within the porous, permeable sedimentary rock is contained here by a layer of impermeable rock then a trap is formed. The movement of geological structures and force of gravity cause these accumulations - called reservoirs - to lie beneath land or oceans.

Although petroleum seeps do exist, such as the one in Figure 1, they are rare. Most petroleum is collected through oil drilling. Once the petroleum has been drilled for by the oil derrick, a pump jack is used to recover the fuel. Once it has been recovered, petroleum must be separated into its different components for use. The main method of separation and refinement of petroleum is fractional distillation.

The separation of petroleum yields many useful products. These products are useful for transportation, fuel oil for heating and electricity generation, and asphalt. Products include gasoline, jet fuel (or kerosene), propane, petroleum coke, bitumen, plastics and waxes.

References

1. Wikimedia Commons. (May 25, 2015). Natural petroleum spring in Slovakia. [Online]. Available: http://en.wikipedia.org/wiki/Petroleum#/media/File:Kor%C5%88ansk%C3%BD_ropn%C3%BD_prame%C5%88.JPG

2. R. Wolfson. (May 25, 2015) Energy, Environment and Climate, 2nd ed. New York, U.S.A.: Norton, 2012, pp. 96-97

3. J. Kraushaar, R. Ristinen. (May 25, 2015). Energy and the Environment, 2nd ed. Hoboken, NJ, U.S.A.: John Wiley & Sons, 2006, pp. 32

4. G. Aubrecht. (May 25, 2015). Energy: Physical, Environmental, and Social Impact, 3rd ed. San Francisco, CA, U.S.A.: Pearson, 2006, pp. 217

5. Pepco. (May 25, 2015). How is crude oil separated into different petroleum products? [Online]. Available: http://www.pepco.ca/blog/index.php/2011/09/25/how-is-crude-oil-separated-into-different-petroleum-products/?lang=en

6. EIA. (May 25, 2015). What are the products and uses of petroleum? [Online]. Available: http://www.eia.gov/tools/faqs/faq.cfm?id=41&t=6

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Petroleum is a broad term that groups together a combination of organic liquids and gases that is formed after kerogen is heated and compressed over long periods of time. This mix can be fairly complex, but the main gaseous component of petroleum is natural gas - largely methane - whereas the main liquid component is crude oil.

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The amount of sunlight that strikes the earth's surface in an hour and a half is enough to handle the entire world's energy consumption for a full year. Solar technologies convert sunlight into electrical energy either through photovoltaic (PV) panels or through mirrors that concentrate solar radiation. This energy can be used to generate electricity or be stored in batteries or thermal storage.

Below, you can find resources and information on the basics of solar radiation, photovoltaic and concentrating solar-thermal power technologies, electrical grid systems integration, and the non-hardware aspects ( soft costs) of solar energy. You can also learn more about how to go solar and the solar energy industry. In addition, you can dive deeper into solar energy and learn about how the U.S. Department of Energy Solar Energy Technologies Office is driving innovative research and development in these areas.

Solar Energy 101

Solar radiation is light - also known as electromagnetic radiation - that is emitted by the sun. While every location on Earth receives some sunlight over a year, the amount of solar radiation that reaches any one spot on the Earth's surface varies. Solar technologies capture this radiation and turn it into useful forms of energy.

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The amount of sunlight that strikes the earth's surface in an hour and a half is enough to handle the entire world's energy consumption for a full year. Solar technologies convert sunlight into electrical energy either through photovoltaic (PV) panels or through mirrors that concentrate solar radiation.

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An increasing number of everyday items are powered with the sun, including backpacks, watches, cars, and airplanes. Also, electricity-generating solar power plants may become an alternative to coal-fired power plants and natural gas power stations in the future.

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How a Solar Cell Works - American Chemical Society

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An increasing number of everyday items are powered with the sun, including backpacks, watches, cars, and airplanes. Also, electricity-generating solar power plants may become an alternative to coal-fired power plants and natural gas power stations in the future.

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Essentials

Earth is bathed in a huge amount of energy from the Sun every day

Photovoltaic solar panels absorb this energy from the Sun and convert it into electricity

A solar cell is made from two layers of silicon-one 'doped' with a tiny amount of added phosphorus (n-type: 'n' for negative), the other with a tiny amount of boron (p-type: 'p' for positive)

The doping ingredients create extra electrons in the n-type layer and 'holes' (missing electrons) in the p-type layer

When photons (light) hit the solar cell, they excite electrons in the n-type layer loose and they travel across to the p-type layer

These electrons can then travel back to the n-type layer, through wires connecting them to an external device, as an electric current that does useful work

Earth is bathed in huge amounts of energy from the Sun-885 million terawatt hours every year. This is a lot-around 6,200 times the amount of commercial primary energy GLOSSARY primary energy Energy in natural sources that has not been converted into other forms by humans. used in the world in 2008. Humans have always used some of the Sun's energy directly-for drying clothes and foodstuffs, for example. They've also utilised it indirectly-through photosynthesis to power the plant growth underpinning the agriculture that supplies us with food and the oxygen we breathe.

And there is another way to use this abundant energy source: photovoltaic (photo = light, voltaic = electricity formed through chemical reaction) solar cells, which allow us to convert sunlight directly into electricity. Since the demonstration of the first silicon photovoltaic cell in 1954, by Daryl Chapin, Calvin Fuller and Gerald Pearson at Bell Laboratories, New Jersey, we have been refining the technology that enables us to harness the reliable, free and clean energy from the Sun.

The first practical silicon photovoltaic cell was developed by Daryl Chapin, Calvin Fuller and Gerald Pearson at Bell Laboratories in 1954.

That first solar cell had an efficiency of around 5 per cent. Many years of solid work have seen that rise to generally around 20 per cent. Solar panels are appearing on more and more rooftops around our suburbs as solar photovoltaics (PV) become an increasingly viable option for domestic electricity production.

Photovoltaic solar cells, such as those in these rooftop panels, convert light directly to electricity. Image source: Marufish / Flickr.

But how exactly does it work? How can sunlight be made to power cars, or to produce the electricity we need for our computers, TVs and toasters?

How photovoltaic cells work

It has been known for more than 150 years that light can have an effect on the electrical properties of some materials. This is called the photoelectric effect. In 1921, Einstein received the Nobel Prize for his work explaining this. Photovoltaic cells are based on a related phenomenon called the photovoltaic effect, and they convert light directly into electricity. Let's look at how.

Most photovoltaic cells are made of silicon, an element that is at the heart of all modern electronics. Silicon is special because of the arrangement of its electrons-it has four out of the possible eight electrons in its outermost shell. This means that it makes perfect covalent bonds with four other silicon atoms, forming a lattice structure.

The outermost electrons in silicon atoms form covalent bonds with each other, creating a lattice structure.

This bonding mechanism means there are very few free electrons floating about, which is what we need to create electricity. That's what electricity actually is, after all-the flow of electrons. Because of the arrangement of bonds in its crystal structure, silicon in its pure form doesn't have very many free electrons, so we 'dope' it.

Doping adds an impurity to the silicon to change the way its atoms are bonded together and share their electrons. Adding small amounts of phosphorus, which has five electrons in its outer shell, as compared with silicon's four, means that the extra (fifth) electron has nothing to bond to, so it's free to roam around and create electric current. Electrons have a negative charge, so when the silicon is doped in this way, it's called a negative material: n-type.

When silicon is doped with elements that have extra electrons in their outermost shell, it produces an n-type material.

We can also dope with boron, which has only three electrons in its outer shell. This leaves one of the bonds with only one electron, creating a 'hole' in the bonding structure. Electrons within the boron-doped silicon can jump around to fill in the hole. Alternatively, the holes themselves can be thought of as moving (in the opposite direction to the electrons) as the electrons hop from one bond to another. This movement also constitutes an electrical current. We now have a material with an overall deficiency of electrons, making a positive (p-type) material.

When silicon is doped with elements that have fewer electrons in their outermost shell, it produces a p-type material.

The extra electrons and holes can float around the lattice; they are 'shared' by all the atoms in the structure. This gives each doped material an overall slight preference to either give or receive electrons. This is known as electronegativity-a measure of how strongly an atom or material hangs on to its electrons.

Through doping, and the resulting changes in electronegativeity, silicon is turned into a conductor of electricity (albeit not a particularly good one).

However, when we put the p-type and the n-type materials in contact with each other, something interesting (and useful) happens. At the point where the two types meet-the junction-electrons from the n-type layer diffuse over into the p-type layer, leaving behind an area with a slight positive charge in the n-type layer. The reverse happens in the p-type layer-holes diffuse into the n-type layer, leaving behind a slight negative charge in a region of the p-type layer. This creates an electric field, which will direct the flow of electric current.

Holes diffuse into the n-type layer, and electrons diffuse into the p-type layer. This creates an electric field at the junction of the two layers.

Now, consider a photovoltaic cell made from a wafer-thin combination of p-type silicon laid over a layer of n-type silicon. When sunlight hits our cell, the energy of its photons excites electrons into states called 'electron-hole pairs'. When these are formed in the vicinity of the electric field at the junction of the p- and n-type layers, the electric field pulls the pair apart (they form a 'charge-separated' state). Controlled by the force of the electric field, the electrons travel to the n-type side, and the holes to the p-type side.

The photons' energy can also create electron-hole pairs in other parts of the doped silicon. Sometimes, these electron-hole pairs will simply pair up again (recombine) with the extra energy emitted as heat. But if they find themselves near the electric field at the junction of the p- and n-type layers, the electric field will send electrons to the n-type layer, and holes to the p-type layer.

If you create an external connection (using electrodes and a wire) between the two layers, the electron will then travel back through the wire to the p-type layer, as an electric current that does useful work. The whole thing acts rather like an electric battery, continually recharged by the sunlight.

Why these particular elements?

Out of all the elements in the periodic table, why use silicon as the main component of a solar cell, and why dope with phosphorus and boron?

Silicon is the most common go-to material for a photovoltaic cell because the maximum wavelength of energy it absorbs is around 800 nanometres, which is close to the peak of the radiation emitted by the Sun. The Sun emits a spectrum of radiation, ranging from around 300 nanometres to 2,000 nanometres, but by far the majority of it is within the range of 420 to 700 nanometres.

The reason why phosphorus and boron are most often used as the doping agents is a bit more complicated. In order to create the flow of electrons within the solar cell, the electrons must be excited out of their stable 'ground' state up into the higher energy level needed for them to move from the p-type to the n-type side. This amount of energy is equivalent to the difference in electronegativity between the two layers (this is called the band gap). Any less and it won't be enough to 'knock' the electron free, and any extra energy would be wasted.

It turns out that the difference in electronegativity between phosphorus-doped and boron-doped silicon is pretty much equal to the energy provided by one photon of sunlight, making them the ideal doping agents for a silicon solar cell.

The quest for efficiency

No method of energy transformation is 100 per cent efficient. Plants convert sunlight into energy with an efficiency of around 5-6 per cent, and a fossil-fuel power plant is only around 30-50 per cent efficient-all the extra energy contained in the fuel it burns is emitted as heat, and effectively wasted.

There a few issues that mean solar cells are not totally efficient in converting sunlight into electrical energy. One is that the energy provided by the photons might be insufficient to allow the electrons to break free from their electron-hole pairs. At other times, the photons might provide more energy than required for the electron to break free, and the excess is wasted. Also, when the electrons break free from their pairs, they often simply recombine with another hole without moving over to the n-type layer.

The ultimate efficiency of a silicon photovoltaic cell in converting sunlight to electrical energy is around 20 per cent, and large areas of solar cells are needed to produce useful amounts of power. The search is therefore on for much cheaper cells without too much of a sacrifice in efficiency.

In 2014, a team from the University of New South Wales set a world record of 40 per cent efficiency using commercially available (traditional single-crystal silicon) solar cells. They developed a method of focusing the sunlight and used a special filter to capture sunlight that is usually wasted.

Several other promising lines have also been pursued by the University of New South Wales. Instead of cutting slices from specially grown silicon single crystals, one possibility involves growing thin films of silicon on much cheaper polycrystalline silicon wafers, or onto glass plates. This process uses 99 per cent less silicon than conventional techniques and is now being utilised commercially in Europe.

In addition, Swinburne University of Technology is developing thin film amorphous silicon, a type of silicon in which the atoms do not form a regular crystalline lattice. With amorphous silicon, thinner layers of silicon can be used, again making the process much cheaper, though less efficient.

A significant focus of activity is in new thin-film solar cell modules that are potentially lighter, more flexible and cheaper than traditional solar cells, which are made on glass. Cadmium telluride and CIGS (copper indium gallium (di)selenide) may well soon challenge traditional silicon modules in both cost and efficiency.

Newly emerging technologies include organic solar cells. The Victorian Organic Solar Cell Consortium (CSIRO, the University of Melbourne and Monash University) is printing solar cells on flexible polymers, rather like the approach to the Australian plastic banknote. Related work is under way at the universities of Newcastle and Queensland.

Solar cells made from the organinc-inorganic combination of methyl-ammonium lead trihalide, with the slightly more manageable name of perovskites, are another fast-growing solar cell technology. CSIRO has recently demonstrated the potential for roll-to-roll printing of perovskites, a method that allows speedy fabrication of the solar cells. The Australian-listed company Dyesol has announced scale-up of perovskites in a joint venture in Turkey, an early step towards these flexible, printable solar cells becoming commercially available.

Perovskite crystal produced in the Los Alamos National Laboratory. Image source: Los Alamos National Laboratory / Flickr.

It's reliable, free and clean, but ...

Solar energy is likely to continue to exist so far into the future that we can think of it as being unending. Essentially, it's renewable, unlike fossil fuels which are running out as we use them.

In addition, using solar energy doesn't cause air pollution or involve damaging the Earth's surface. It requires no difficult and expensive extraction procedures. Creating the solar cells themselves does require resources-converting sand into silicon still requires considerable energy-but this is paid back within three or four years of a solar cell's operation.

But the main problem is what to do when the Sun doesn't shine. Although we consume a considerable amount of electricity during the day (especially for air-conditioning during hot summers) when the Sun is readily available, we also need storage to tide us over on cloudy days and at night-time. On a domestic scale, the frontrunner in batteries to complement a rooftop solar panel set-up is currently the Tesla Powerwall. There are some other strong contenders in the products being rolled out by Panasonic and LG Chem.

Australia's solar future

Australia receives the most solar radiation per square metre of any continent in the world (although the Red Sea area, including Egypt and Saudi Arabia, has the highest solar energy potential). While there are now more than one million rooftop solar systems installed around Australia, according to figures from the International Energy Agency, photovoltaic solar only contributed around 0.6 per cent of Australia's energy in 2012.

Even areas in southern Australia have extremely high potential for solar resources. The state of Victoria has a greater solar potential than Germany, which currently has the highest installed solar capacity of any country in the world. The Climate Commission's report about solar energy in Australia (PDF) states that the amount of solar radiation Australia receives in a year is around 10,000 times the national energy consumption, and that an area of just 20,000 square kilometres would be enough to provide the country with its energy needs.

We've clearly got an abundant resource at our fingertips. We just need to harness it.

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Essentials Earth is bathed in a huge amount of energy from the Sun every day Photovoltaic solar panels absorb this energy from the Sun and convert it into electricity A solar cell is made from two layers of silicon-one 'doped' with a tiny amount of added phosphorus (n-type: 'n' for

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From massive wind farms generating power to small turbines powering a single home, wind turbines around the globe generate clean electricity for a variety of power needs.

In the United States, wind turbines are becoming a common sight. Since the turn of the century, total U.S. wind power capacity has increased more than 24-fold. Currently, there's enough wind power capacity in the U.S. to generate enough electricity to power more than 15 million homes, helping pave the way to a clean energy future.

What is a Wind Turbine?

The concept of harnessing wind energy to generate mechanical power goes back for millennia. As early as 5000 B.C., Egyptians used wind energy to propel boats along the Nile River. American colonists relied on windmills to grind grain, pump water and cut wood at sawmills. Today's wind turbines are the windmill's modern equivalent -- converting the kinetic energy in wind into clean, renewable electricity.

How Does a Wind Turbine Work?

The majority of wind turbines consist of three blades mounted to a tower made from tubular steel. There are less common varieties with two blades, or with concrete or steel lattice towers. At 100 feet or more above the ground, the tower allows the turbine to take advantage of faster wind speeds found at higher altitudes.

Turbines catch the wind's energy with their propeller-like blades, which act much like an airplane wing. When the wind blows, a pocket of low-pressure air forms on one side of the blade. The low-pressure air pocket then pulls the blade toward it, causing the rotor to turn. This is called lift. The force of the lift is much stronger than the wind's force against the front side of the blade, which is called drag. The combination of lift and drag causes the rotor to spin like a propeller.

A series of gears increase the rotation of the rotor from about 18 revolutions a minute to roughly 1,800 revolutions per minute -- a speed that allows the turbine's generator to produce AC electricity.

A streamlined enclosure called a nacelle houses key turbine components -- usually including the gears, rotor and generator -- are found within a housing called the nacelle. Sitting atop the turbine tower, some nacelles are large enough for a helicopter to land on.

Another key component is the turbine's controller, that keeps the rotor speeds from exceeding 55 mph to avoid damage by high winds. An anemometer continuously measures wind speed and transmits the data to the controller. A brake, also housed in the nacelle, stops the rotor mechanically, electrically or hydraulically in emergencies. Explore the interactive graphic above to learn more about the mechanics of wind turbines.

Types of Wind Turbines

There are two basic types of wind turbines: those with a horizontal axis, and those with a a vertical axis.

The majority of wind turbines have a horizontal axis: a propeller-style design with blades that rotate around a horizontal axis. Horizontal axis turbines are either upwind (the wind hits the blades before the tower) or downwind (the wind hits the tower before the blades). Upwind turbines also include a yaw drive and motor -- components that turns the nacelle to keep the rotor facing the wind when its direction changes.

While there are several manufacturers of vertical axis wind turbines, they have not penetrated the utility scale market (100 kW capacity and larger) to the same degree as horizontal access turbines. Vertical axis turbines fall into two main designs:

Drag-based, or Savonius, turbines generally have rotors with solid vanes that rotate about a vertical axis.

Lift-based, or Darrieus, turbines have a tall, vertical airfoil style (some appear to have an eggbeater shape). The Windspire is a type of lift-based turbine that is undergoing independent testing at the National Renewable Energy Laboratory's National Wind Technology Center.

Wind Turbine Applications

Wind Turbines are used in a variety of applications - from harnessing offshore wind resources to generating electricity for a single home:

Large wind turbines, most often used by utilities to provide power to a grid, range from 100 kilowatts to several megawatts. These utility-scale turbines are often grouped together in wind farms to produce large amounts of electricity. Wind farms can consist of a few or hundreds of turbines, providing enough power for tens of thousands of homes.

Small wind turbines, up to 100 kilowatts, are typically close to where the generated electricity will be used, for example, near homes, telecommunications dishes or water pumping stations. Small turbines are sometimes connected to diesel generators, batteries and photovoltaic systems. These systems are called hybrid wind systems and are typically used in remote, off-grid locations, where a connection to the utility grid is not available.

Offshore wind turbines are used in many countries to harness the energy of strong, consistent winds found off of coastlines. The technical resource potential of the winds above U.S. coastal waters is enough to provide more than 4,000 gigawatts of electricity, or approximately four times the generating capacity of the current U.S. electric power system. Although not all of these resources will be developed, this represents a major opportunity to provide power to highly populated coastal cities. To take advantage of America's vast offshore wind resources, the Department is investing in three offshore wind demonstration projects designed to deploy offshore wind systems in federal and state waters by 2017.

Future of Wind Turbines

To ensure future growth of the U.S. wind industry, the Energy Department's Wind Program works with industry partners to improve the reliability and efficiency of wind turbine technology, while also reducing costs. The program's research efforts have helped to increase the average capacity factor (a measure of power plant productivity) from 22 percent for wind turbines installed before 1998 to more than 32 percent for turbines installed between 2006 and 2012. Wind energy costs have been reduced from more than 55 cents per kilowatt-hour (kWh) in 1980 to under 6 cents/kWh today in areas with good wind resources.

Wind turbines offer a unique opportunity to harness energy in areas where our country's populations need it most. This includes offshore wind's potential to provide power to population centers near coastlines, and land-based wind's ability to deliver electricity to rural communities with few other local sources of low carbon power.

The Energy Department continues working to deploy wind power in new areas on land and at sea and ensuring the stable, secure integration of this power into our nation's electrical grid.

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From massive wind farms generating power to small turbines powering a single home, wind turbines around the globe generate clean electricity for a variety of power needs. In the United States, wind turbines are becoming a common sight. Since the turn of the century, total U.S. wind power capacity has increased more than 24-fold.

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What is Hydropower?

Hydropower, or hydroelectric power, is one of the oldest and largest sources of renewable energy, which uses the natural flow of moving water to generate electricity. Hydropower currently accounts for 28.7% of total U.S. renewable electricity generation and about 6.2% of total U.S. electricity generation.

While most people might associate the energy source with the Hoover Dam-a huge facility harnessing the power of an entire river behind its wall- hydropower facilities come in all sizes. Some may be very large, but they can be tiny, too, taking advantage of water flows in municipal water facilities or irrigation ditches. They can even be "damless," with diversions or run-of-river facilities that channel part of a stream through a powerhouse before the water rejoins the main river. Whatever the method, hydropower is much easier to obtain and more widely used than most people realize. In fact, all but two states (Delaware and Mississippi) use hydropower for electricity, some more than others. For example, in 2020 about 66% of the state of Washington's electricity came from hydropower.

In a study led by the National Renewable Energy Laboratory on hydropower flexibility, preliminary analysis found that the firm capacity associated with U.S. hydropower's flexibility is estimated to be over 24 GW. To replace this capability with storage would require the buildout of 24 GW of 10-hour storage-more than all the existing storage in the United States today. Additionally, in terms of integrating wind and solar, the flexibility presented in existing U.S. hydropower facilities could help bring up to 137 gigawatts of new wind and solar online by 2035.

How Does Hydropower Work?

Hydropower technologies generate power by using the elevation difference, created by a dam or diversion structure, of water flowing in on one side and out, far below, on the other. The Department of Energy's "Hydropower 101" video explains how hydropower works and highlights some of the research and development efforts of the Water Power Technologies Office (WPTO) in this area.

What is the cost of Hydropower?

Hydropower is an affordable source of electricity that costs less than most. Since hydropower relies only on the energy from moving water, states that get the majority of their electricity from hydropower, like Idaho, Washington, and Oregon, have lower energy bills than the rest of the country.

Compared to other electricity sources, hydropower also has relatively low costs throughout the duration of a full project lifetime in terms of maintenance, operations, and fuel. Like any major energy source, significant upfront costs are unavoidable, but hydropower's longer lifespan spreads these costs out over time. Additionally, the equipment used at hydropower facilities often operates for longer periods of time without needing replacements or repairs, saving money in the long term.

The installation costs for large hydropower facilities consist mostly of civil construction works (such as the building of the dams, tunnels, and other necessary infrastructure) and electromechanical equipment costs (electricity-generating machinery). Since hydropower is a site-specific technology, these costs can be minimized at the planning stage through proper selection of location and design.

WHAT ARE THE BENEFITS OF HYDROPOWER?

The benefits of hydropower have been recognized and harnessed for thousands of years. In addition to being a clean and cost-effective form of energy, hydropower plants can provide power to the grid immediately, serving as a flexible and reliable form of backup power during major electricity outages or disruptions. Hydropower also produces a number of benefits outside of electricity generation, such as flood control, irrigation support, and water supply.

WHAT IS THE HISTORY OF HYDROPOWER?

The history of hydropower dates back thousands of years. For example, the Greeks used water wheels to grind wheat into flour more than 2,000 years ago. The evolution of the modern hydropower turbine began in the mid-1700s when a French hydraulic and military engineer, Bernard Forest de Bélidor, wrote Architecture Hydraulique. Many key developments in hydropower technology occurred during the first half of the 19th century, and more recently, the past century has seen a number of hydroelectric advancements that have helped hydropower become an integral part of the renewable energy mix in the United States.

To learn how to join the hydropower industry and more about science, technology, engineering, and mathematics (STEM) workforce development opportunities, visit the Hydropower STEM Portal.

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Hydropower, or hydroelectric power, is one of the oldest and largest sources of renewable energy, which uses the natural flow of moving water to generate electricity.

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Hydropower is energy in moving water

People have a long history of using the force of water flowing in streams and rivers to produce mechanical energy. Hydropower was one of the first sources of energy used for electricity generation, and until 2019, hydropower was the leading source of total annual U.S. renewable electricity generation.

In 2022, hydroelectricity accounted for about 6.2% of total U.S. utility-scale ¹ electricity generation and 28.7% of total utility-scale renewable electricity generation. Hydroelectricity generation varies annually, and it's share of total U.S. electricity generation generally decreased from the 1950's through 2020, mainly because of increases in electricity generation from other sources. Hydroelectricity's percentage share of total annual U.S. electricity generation in 2001 through 2022 averaged about 6.7%.

Hydropower relies on the water cycle

Solar energy heats water on the surface of rivers, lakes, and oceans, which causes the water to evaporate.

Water vapor condenses into clouds and falls as precipitation-rain and snow.

Precipitation collects in streams and rivers, which empty into oceans and lakes, where it evaporates and begins the cycle again.

The amount of precipitation that drains into rivers and streams in a geographic area determines the amount of water available for producing hydropower. Seasonal variations in precipitation and long-term changes in precipitation patterns, such as droughts, can have significant effects on the availability of hydropower production.

Hydroelectric power is produced with moving water

Because the source of hydroelectric power is water, hydroelectric power plants are usually located on or near a water source. The volume of the water flow and the change in elevation-or fall, and often referred to as head -from one point to another determine the amount of available energy in moving water. In general, the greater the water flow and the higher the head, the more electricity a hydropower plant can produce.

At hydropower plants water flows through a pipe, or penstock, then pushes against and turns blades in a turbine that spin to power a generator to produce electricity.

Conventional hydroelectric facilities include:

Run-of-the-river systems, where the force of the river's current applies pressure on a turbine. The facilities may have a in the water course to divert water flow to hydro turbines.

Storage systems, where water accumulates in reservoirs created by dams on streams and rivers and is released through hydro turbines as needed to generate electricity. Most U.S. hydropower facilities have dams and storage reservoirs.

Pumped-storage hydropower facilities are a type of hydroelectric storage system where water is pumped from a water source up to a storage reservoir at a higher elevation. The water is released from the upper reservoir to power hydro turbines located below the upper reservoir. They usually pump water to storage when electricity demand and generation costs, or when wholesale electricity prices are relatively low, and release the stored water to generate electricity during peak electricity demand periods when wholesale electricity prices are relatively high. Pumped-storage hydroelectric systems generally use more electricity to pump water to the upper water storage reservoirs than they produce with the stored water. Therefore, pumped-storage facilities have net negative electricity generation balances.

Hydropower has a long history

Hydropower is one of the oldest sources of energy for producing mechanical and electrical energy, and up until 2019, it was the largest source of total annual U.S. renewable electricity generation. Thousands of years ago, people used hydropower to turn paddle wheels on rivers to grind grain. Before steam power and electricity were available in the United States, grain and lumber mills were powered directly with hydropower. The first industrial use of hydropower to generate electricity in the United States was in 1880 to power 16 brush-arc lamps at the Wolverine Chair Factory in Grand Rapids, Michigan. The first U.S. hydroelectric power plant to sell electricity opened on the Fox River near Appleton, Wisconsin, on September 30, 1882.

There are about 1,450 conventional and 40 pumped-storage hydropower plants operating in the United States. The oldest operating U.S. hydropower facility is the Whiting plant in Whiting, Wisconsin, which started operating in 1891 and has a total generation capacity of about 4 megawatts (MW). Most U.S. hydroelectricity is produced at large dams on major rivers, and most of these hydroelectric dams were built before the mid-1970s by federal government agencies. The largest U.S. hydropower facility, and the largest U.S. electric power plant in electric generation capacity, is the Grand Coulee hydro dam on the Columbia River in Washington State, with 6,765 MW total generation capacity.
Last updated: April 20, 2023, with most recent data available.

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The water cycle and its importance to understanding hydropower and how hydroelectricity is generated.

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Geothermal technology extracts the heat found within the subsurface of the earth, which can be used directly for heating and cooling, or converted into electricity. However, to generate electricity, medium- or high-temperature resources are needed. These are usually located close to tectonically act…

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On these pages you’ll find helpful publications, software, and websites for the geothermal community and stakeholders.

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People have used biomass energy-energy from living things-since the earliest "cave men" first made wood fires for cooking or keeping warm.

Biomass is organic, meaning it is made of material that comes from living organisms, such as plants and animals. The most common biomass materials used for energy are plants, wood, and waste. These are called biomass feedstocks. Biomass energy can also be a non-renewable energy source.

Biomass contains energy first derived from the sun: Plants absorb the sun's energy through photosynthesis, and convert carbon dioxide and water into nutrients (carbohydrates).

The energy from these organisms can be transformed into usable energy through direct and indirect means. Biomass can be burned to create heat (direct), converted into electricity (direct), or processed into biofuel (indirect).

Thermal Conversion

Biomass can be burned by thermal conversion and used for energy. Thermal conversion involves heating the biomass feedstock in order to burn, dehydrate, or stabilize it. The most familiar biomass feedstocks for thermal conversion are raw materials such as municipal solid waste (MSW) and scraps from paper or lumber mills.

Different types of energy are created through direct firing, co-firing, pyrolysis, gasification, and anaerobic decomposition.

Before biomass can be burned, however, it must be dried. This chemical process is called torrefaction. During torrefaction, biomass is heated to about 200° to 320° Celsius (390° to 610° Fahrenheit). The biomass dries out so completely that it loses the ability to absorb moisture, or rot. It loses about 20% of its original mass, but retains 90% of its energy. The lost energy and mass can be used to fuel the torrefaction process.

During torrefaction, biomass becomes a dry, blackened material. It is then compressed into briquettes. Biomass briquettes are very hydrophobic, meaning they repel water. This makes it possible to store them in moist areas. The briquettes have high energy density and are easy to burn during direct or co-firing.

Direct Firing and Co-Firing
Most briquettes are burned directly. The steam produced during the firing process powers a turbine, which turns a generator and produces electricity. This electricity can be used for manufacturing or to heat buildings.

Biomass can also be co-fired, or burned with a fossil fuel. Biomass is most often co-fired in coal plants. Co-firing eliminates the need for new factories for processing biomass. Co-firing also eases the demand for coal. This reduces the amount of carbon dioxide and other greenhouse gases released by burning fossil fuels.

Pyrolysis
Pyrolysis is a related method of heating biomass. During pyrolysis, biomass is heated to 200° to 300° C (390° to 570° F) without the presence of oxygen. This keeps it from combusting and causes the biomass to be chemically altered.

Pyrolysis produces a dark liquid called pyrolysis oil, a synthetic gas called syngas, and a solid residue called biochar. All of these components can be used for energy.

Pyrolysis oil, sometimes called bio-oil or biocrude, is a type of tar. It can be combusted to generate electricity and is also used as a component in other fuels and plastics. Scientists and engineers are studying pyrolysis oil as a possible alternative to petroleum.

Syngas can be converted into fuel (such as synthetic natural gas). It can also be converted into methane and used as a replacement for natural gas.

Biochar is a type of charcoal. Biochar is a carbon-rich solid that is particularly useful in agriculture. Biochar enriches soil and prevents it from leaching pesticides and other nutrients into runoff. Biochar is also an excellent carbon sink. Carbon sinks are reservoirs for carbon-containing chemicals, including greenhouse gases.

Gasification
Biomass can also be directly converted to energy through gasification. During the gasification process, a biomass feedstock (usually MSW) is heated to more than 700° C (1,300° F) with a controlled amount of oxygen. The molecules break down, and produce syngas and slag.

Syngas is a combination of hydrogen and carbon monoxide. During gasification, syngas is cleaned of sulfur, particulates, mercury, and other pollutants. The clean syngas can be combusted for heat or electricity, or processed into transportation biofuels, chemicals, and fertilizers.

Slag forms as a glassy, molten liquid. It can be used to make shingles, cement, or asphalt.

Industrial gasification plants are being built all over the world. Asia and Australia are constructing and operating the most plants, although one of the largest gasification plants in the world is currently under construction in Stockton-on-Tees, England. This plant will eventually be able to convert more than 350,000 tons of MSW into enough energy to power 50,000 homes.

Anaerobic Decomposition
Anaerobic decomposition is the process where microorganisms, usually bacteria, break down material in the absense of oxygen. Anaerobic decomposition is an important process in landfills, where biomass is crushed and compressed, creating an anaerobic (or oxygen-poor) environment.

In an anaerobic environment, biomass decays and produces methane, which is a valuable energy source. This methane can replace fossil fuels.

In addition to landfills, anaerobic decomposition can also be implemented on ranches and livestock farms. Manure and other animal waste can be converted to sustainably meet the energy needs of the farm.

Biofuel

Biomass is the only renewable energy source that can be converted into liquid biofuels such as ethanol and biodiesel. Biofuel is used to power vehicles, and is being produced by gasification in countries such as Sweden, Austria, and the United States.

Ethanol is made by fermenting biomass that is high in carbohydrates, such as sugar cane, wheat, or corn. Biodiesel is made from combining ethanol with animal fat, recycled cooking fat, or vegetable oil.

Biofuels do not operate as efficiently as gasoline. However, they can be blended with gasoline to efficiently power vehicles and machinery, and do not release the emissions associated with fossil fuels.

Ethanol requires acres of farmland to grow biocrops (usually corn). About 1,515 liters (400 gallons) of ethanol is produced by an acre of corn. But this acreage is then unavailable for growing crops for food or other uses. Growing enough corn for ethanol also creates a strain on the environment because of the lack of variation in planting, and the high use of pesticides.

Ethanol has become a popular substitute for wood in residential fireplaces. When it is burned, it gives off heat in the form of flames, and water vapor instead of smoke.

Biochar

Biochar, produced during pyrolysis, is valuable in agricultural and environmental use.

When biomass rots or burns (naturally or by human activity), it releases high amounts of methane and carbon dioxide into the atmosphere. However, when biomass is charred, it sequesters, or stores, its carbon content. When biochar is added back to the soil, it can continue to absorb carbon and form large underground stores of sequestered carbon-carbon sinks-that can lead to negative carbon emissions and healthier soil.

Biochar also helps enrich the soil. It is porous. When added back to the soil, biochar absorbs and retains water and nutrients.

Biochar is used in Brazil's Amazon rain forest in a process called slash-and-char. Slash-and-char agriculture replaces slash-and-burn, which temporarily increases the soil nutrients but causes it to lose 97% of its carbon content. During slash-and-char, the charred plants (biochar) are returned to the soil, and the soil retains 50% of its carbon. This enhances the soil and leads to significantly higher plant growth.

Black Liquor

When wood is processed into paper, it produces a high-energy, toxic substance called black liquor. Until the 1930s, black liquor from paper mills was considered a waste product and dumped into nearby water sources.

However, black liquor retains more than 50% of the wood's biomass energy. With the invention of the recovery boiler in the 1930s, black liquor could be recycled and used to power the mill. In the U.S., paper mills use nearly all their black liquor to run their mills, and the forest industry is one of the most energy-efficient in the nation as a result.

More recently, Sweden has experimented in gasifying black liquor to produce syngas, which can then be used to generate electricity.

Hydrogen Fuel Cells

Biomass is rich in hydrogen, which can be chemically extracted and used to generate power and to fuel vehicles. Stationary fuel cells are used to generate electricity in remote locations, such as spacecraft and wilderness areas. Yosemite National Park in the U.S. state of California, for example, uses hydrogen fuel cells to provide electricity and hot water to its administration building.

Hydrogen fuel cells may hold even more potential as an alternative energy source for vehicles. The U.S. Department of Energy estimates that biomass has the potential to produce 40 million tons of hydrogen per year. This would be enough to fuel 150 million vehicles.

Currently, hydrogen fuel cells are used to power buses, forklifts, boats, and submarines, and are being tested on airplanes and other vehicles.

However, there is a debate as to whether this technology will become sustainable or economically possible. The energy that it takes to isolate, compress, package, and transport the hydrogen does not leave a high quantity of energy for practical use.

Biomass and the Environment

Biomass is an integral part of Earth's carbon cycle. The carbon cycle is the process by which carbon is exchanged between all layers of the Earth: atmosphere, hydrosphere, biosphere, and lithosphere.

The carbon cycle takes many forms. Carbon helps regulate the amount of sunlight that enters Earth's atmosphere. It is exchanged through photosynthesis, decomposition, respiration, and human activity. Carbon that is absorbed by soil as an organism decomposes, for example, may be recycled as a plant releases carbon-based nutrients into the biosphere through photosynthesis. Under the right conditions, the decomposing organism may become peat, coal, or petroleum before being extracted through natural or human activity.

Between periods of exchange, carbon is sequestered, or stored. The carbon in fossil fuels has been sequestered for millions of years. When fossil fuels are extracted and burned for energy, their sequestered carbon is released into the atmosphere. Fossil fuels do not re-absorb carbon.

In contrast to fossil fuels, biomass comes from recently living organisms. The carbon in biomass can continue to be exchanged in the carbon cycle.

In order to effectively allow Earth to continue the carbon cycle process, however, biomass materials such as plants and forests have to be sustainably farmed. It takes decades for trees and plants such as switchgrass to re-absorb and sequester carbon. Uprooting or disturbing the soil can be extremely disruptive to the process. A steady and varied supply of trees, crops, and other plants is vital for maintaining a healthy environment.

Algal Fuel

Algae is a unique organism that has enormous potential as a source of biomass energy. Algae, whose most familiar form is seaweed, produces energy through photosynthesis at a much quicker rate than any other biofuel feedstock-up to 30 times faster than food crops!

Algae can be grown in ocean water, so it does not deplete freshwater resources. It also does not require soil, and therefore does not reduce arable land that could potentially grow food crops. Although algae releases carbon dioxide when it is burned, it can be farmed and replenished as a living organism. As it is replenished, it releases oxygen, and absorbs pollutants and carbon emissions.

Algae takes up much less space than other biofuel crops. The U.S. Department of Energy estimates that it would only take approximately 38,850 square kilometers (15,000 square miles, an area less than half the size of the U.S. state of Maine) to grow enough algae to replace all petroleum-fueled energy needs in the United States.

Algae contains oils that can be converted to a biofuel. At the Aquaflow Bionomic Corporation in New Zealand, for example, algae is processed with heat and pressure. This creates a " green crude," which has similar properties to crude oil, and can be used as a biofuel.

Algae's growth, photosynthesis, and energy production increases when carbon dioxide is bubbled through it. Algae is an excellent filter that absorbs carbon emissions. Bioenergy Ventures, a Scottish firm, has developed a system in which carbon emissions from a whiskey distillery are funneled to an algae pool. The algae flourishes with the additional carbon dioxide. When the algae die (after about a week) they are collected, and their lipids (oils) are converted into biofuel or fish food.

Algae has enormous potential as an alternative energy source. However, processing it into usable forms is expensive. Although it is estimated to yield 10 to 100 times more fuel than other biofuel crops, in 2010 it cost $5,000 a ton. The cost will likely come down, but it is currently out of reach for most developing economies.

People and Biomass

Advantages
Biomass is a clean, renewable energy source. Its initial energy comes from the sun, and plants or algae biomass can regrow in a relatively short amount of time. Trees, crops, and municipal solid waste are consistently available and can be managed sustainably.

If trees and crops are sustainably farmed, they can offset carbon emissions when they absorb carbon dioxide through respiration. In some bioenergy processes, the amount of carbon that is re-absorbed even exceeds the carbon emissions that are released during fuel processing or usage.

Many biomass feedstocks, such as switchgrass, can be harvested on marginal lands or pastures, where they do not compete with food crops.

Unlike other renewable energy sources, such as wind or solar, biomass energy is stored within the organism, and can be harvested when it is needed.

Disadvantages
If biomass feedstocks are not replenished as quickly as they are used, they can become non-renewable. A forest, for instance, can take hundreds of years to re-establish itself. This is still a much, much shorter time period than a fossil fuel such as peat. It can take 900 years for just a meter (3 feet) of peat to replenish itself.

Most biomass requires arable land to develop. This means that land used for biofuel crops such as corn and soybeans are unavailable to grow food or provide natural habitats.

Forested areas that have matured for decades (so-called " old-growth forests") are able to sequester more carbon than newly planted areas. Therefore, if forested areas are not sustainably cut, re-planted, and given time to grow and sequester carbon, the advantages of using the wood for fuel are not offset by the trees' regrowth.

Most biomass plants require fossil fuels to be economically efficient. An enormous plant under construction near Port Talbot, Wales, for instance, will require fossil fuels imported from North America, offsetting some of the sustainability of the enterprise.

Biomass has a lower " energy density" than fossil fuels. As much as 50% of biomass is water, which is lost in the energy conversion process. Scientists and engineers estimate that it is not economically efficient to transport biomass more than 160 kilometers (100 miles) from where it is processed. However, converting biomass into pellets (as opposed to wood chips or larger briquettes) can increase the fuel's energy density and make it more advantageous to ship.

Burning biomass releases carbon monoxide, carbon dioxide, nitrogen oxides, and other pollutants and particulates. If these pollutants are not captured and recycled, burning biomass can create smog and even exceed the number of pollutants released by fossil fuels.

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Mary Crooks, National Geographic Society

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Last Updated

Nov. 19, 2012

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Andrew Turgeon
Elizabeth Morse

Jeannie Evers, Emdash Editing

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People have used biomass energy-energy from living things-since the earliest "cave men" first made wood fires for cooking or keeping warm. Biomass is organic, meaning it is made of material that comes from living organisms, such as plants and animals. The most common biomass materials used for energy are plants, wood, and waste.

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Biomass-renewable energy from plants and animals

Biomass is renewable organic material that comes from plants and animals. Biomass contains stored chemical energy from the sun that is produced by plants through photosynthesis. Biomass can be burned directly for heat or converted to liquid and gaseous fuels through various processes

Biomass was the largest source of total annual U.S. energy consumption until the mid-1800s. In 2022, biomass accounted for nearly 5% of U.S. total primary energy consumption. Biomass is used for heating and electricity generation and as a transportation fuel. Biomass is an important fuel in many countries, especially for cooking and heating in developing countries.

Wood and wood processing waste-firewood, wood pellets, and wood chips, lumber and furniture mill sawdust and waste, and black liquor from pulp and paper mills

Agricultural crops and waste materials-corn, soybeans, sugar cane, switchgrass, woody plants, algae, and crop and food processing residues, mostly to produce biofuels

Biogenic materials in municipal solid waste-paper products; cotton and wool products; and food, yard, and wood wastes

Animal manure and human sewage for producing biogas (renewable natural gas)

Biomass can be converted to energy in different ways

Biomass is converted to energy through various processes, including:

Direct combustion (burning) to produce heat

Thermochemical conversion to produce solid, gaseous, and liquid fuels

Chemical conversion to produce liquid fuels

Biological conversion to produce liquid and gaseous fuels

Direct combustion is the most common method for converting biomass to useful energy. All biomass can be burned directly for heating buildings and water, for providing industrial process heat, and for generating electricity in steam turbines.

Thermochemical conversion of biomass includes pyrolysis and gasification. Both processes are thermal decomposition processes wherein biomass feedstock materials are heated in closed, pressurized vessels called gassifiers at high temperatures. The processes mainly differ in the temperatures and in the amount of oxygen present during conversion.

Pyrolysis entails heating organic materials to between 800&deg F and 900&deg F (400&deg C and 500&deg C) in the nearly complete absence of free oxygen. Biomass pyrolysis produces fuels such as charcoal, bio-oil, renewable diesel, methane, and hydrogen.

Hydrotreating is used to process bio-oil (produced by fast pyrolysis) with hydrogen under elevated temperatures and pressures in the presence of a catalyst to produce renewable diesel, renewable gasoline, and renewable jet fuel.

Gasification entails heating organic materials to between 1,400&deg F and 1,700 F (800&deg C and 900&deg C) with injections of controlled amounts of free oxygen or steam into the vessel to produce a carbon monoxide- and hydrogen-rich gas called synthesis gas or syngas. Syngas can be used as a fuel for diesel engines, for heating, and for generating electricity in gas turbines. It can also be treated to separate the hydrogen from the gas, and the hydrogen can be burned or used in fuel cells. The syngas can be further processed to produce liquid fuels using the Fischer-Tropsch process.

A chemical conversion process known as transesterification is used for converting vegetable oils, animal fats, and greases into fatty acid methyl esters (FAME) to produce biodiesel.

Biological conversion of biomass includes fermentation to make ethanol and anaerobic digestion to produce biogas. Ethanol is used as a vehicle fuel. Biogas, also called biomethane or renewable natural gas, is produced in anaerobic digesters at sewage treatment plants and at dairy and livestock operations. It also forms in and may be captured from solid waste landfills. Properly treated renewable natural gas has the same uses as fossil fuel natural gas.

Researchers are working on ways to improve these methods and to develop other ways to convert and use more biomass for energy.

Biomass provided about 5% of U.S. energy in 2022

In 2022, biomass accounted for 5% of U.S. energy consumption, or about 4,930 trillion British thermal units (TBtu). The types, amounts, and the percentage shares of total biomass energy consumption in 2022 were:

Biofuels-2,419 TBtu-49%

Wood and wood waste-1,984 TBtu-43%

Municipal solid waste, animal manure, and sewage-411 TBtu-8%

The industrial sector is the largest consumer of biomass for energy in the United States

The amounts-in TBtu-and percentage shares of total U.S. biomass energy use by consuming sector in 2022 were:

The industrial sector accounted for the most, in terms of energy content and percentage share, of total annual U.S. biomass consumption in 2022. The wood products and paper industries use biomass in combined heat and power plants for process heat and to generate electricity for their own use.

The transportation sector accounted for the second-highest amount and percentage share of biomass (as biofuels) consumption in 2022.

The residential and commercial sectors use firewood and wood pellets for heating. The commercial sector also consumes, and in some cases, sells renewable natural gas produced at municipal sewage treatment facilities and at waste landfills.

The electric power sector uses wood and biomass-derived wastes to generate electricity for sale to the other sectors.

The United States is a net exporter of biomass energy

On an energy content basis, U.S. total biomass energy exports exceeded total biomass energy imports in 2022.

Densified biomass fuels (wood pellets and other densified biomass fuels) have become a U.S. export commodity in recent years. In 2022, the United States exported about 8.8 million tons of wood fuel pellets ( Table 8).
Last updated: June 30, 2023, with data from the Monthly Energy Review, April 2023; data for 2022 are preliminary.

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How is biomass, such as plants, wood, paper and lumber mills waste, and municipal garbage converted into heat, into biogas, or into liquid biofuels.