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Can you guess the 14 other things we do at VIMSIA besides solar that make us a "GREEN" School? Click and peek to see how many you guessed...

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The Federal Environmental Protection Agency (EPA), Middle States Association of Colleges and Schools, as well as numerous local entities, have recognized VIMSIA's environmental efforts.

The USVI, like states in the mainland, is constantly in need of education funding. A major deterrent to a viable Virgin Islands economy is the high cost of energy. VI energy costs are the highest in the country at 48 cents/kw.

An environmentally friendly school that offers an alternative education to public school is much needed. VIMSIA is proud to have been on the leading edge of the solar movement in St. Thomas. Our first 6KW array in 2007 set the stage for what has become a 212KW array in 2019.

We put sustainability at the forefront of our campus operations. Water is collected from our rooftops and stored in cisterns - some for drinking and everyday use, some, like the water collected from our solar awning and our parking lot, is used as a greywater irrigation system for our soccer field.

A retention pond built below the field promotes groundwater retention and reduces runoff from our surrounding neighborhood watershed. We have worked with Fish and Wildlife to create a tree boa preserve on our property to protect this endangered indigenous species. Hundreds of pounds of aluminum cans have been recycled on our island thanks to the efforts our student recycling program.

Our students participate annually in UVI's Reef Fest - which focuses on marine environmental issues. Reefs are an essential part of a healthy ecosystem in the USVI. Every effort from our community is needed to protect them.

Take a virtual tour of our campus below, and see for yourself how we strive to be a truly green school.

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The Federal Environmental Protection Agency (EPA), Middle States Association of Colleges and Schools, as well as numerous local entities, have recognized VIMSIA's environmental efforts. The USVI, like states in the mainland, is constantly in need of education funding. A major deterrent to a viable Virgin Islands economy is the high cost of energy.

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How do solar panels work? - Richard Komp

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Energy from the sun

The sun has produced energy for billions of years and is the ultimate source for all of the energy sources and fuels that we use today. People have used the sun's rays (solar radiation) for thousands of years for warmth and to dry meat, fruit, and grains. Over time, people developed technologies to collect solar energy for heat and to convert it into electricity.

Collecting and using solar thermal (heat) energy

An example of an early solar energy collection device is the solar oven (a box for collecting and absorbing sunlight). In the 1830s, British astronomer John Herschel used a solar oven to cook food during an expedition to Africa. People now use many different technologies for collecting and converting solar radiation into heat energy for a many uses.

Water for use in homes, buildings, or swimming pools

The inside of homes, greenhouses, and other buildings

Fluids to high temperatures in solar thermal power plants

Solar photovoltaic systems convert sunlight into electricity

Solar photovoltaic (PV) devices, or solar cells, change sunlight directly into electricity. Small PV cells can power calculators, watches, and other small electronic devices. Arrangements of many solar cells in PV panels and arrangements of multiple PV panels in PV arrays can produce electricity for an entire house. Some PV power plants have large arrays that cover many acres to produce electricity for thousands of homes.

Solar energy has benefits and some limitations

Solar energy systems do not produce air pollutants or carbon dioxide.

Solar energy systems on buildings have minimal effects on the environment.

The amount of sunlight that arrives at the earth's surface is not constant. The amount of sunlight varies depending on location, time of day, season of the year, and weather conditions.

The amount of sunlight reaching a square foot of the earth's surface is relatively small, so a large surface area is necessary to absorb or collect a useful amount of energy.

Solar energy is sunshine

Sunshine is radiant energy from the sun. The amount of solar radiation, or solar energy, that the earth receives each day is many times greater than the total amount of all energy that people consume each day. Use of solar energy, especially for electricity generation, has increased a lot in the United States and around the world in the past 30 years.

Latitude, climate, and weather patterns are major factors that affect insolation -the amount of solar radiation received on a given surface area during a specific amount of time. Locations nearer the equator and in arid climates generally receive higher amounts of insolation than other locations. Clouds, dust, volcanic ash, and pollution in the atmosphere affect insolation levels at the surface. Buildings, trees, and mountains may shade a location during different times of the day in different months of the year. Seasonal (monthly) variations in solar resources increase with increasing distance from the earth's equator.

The type of solar collector also determines the type of solar radiation and level of insolation that a solar collector receives. Concentrating solar collector systems, such as those used in solar thermal-electric power plants, require direct solar radiation, which is generally greater in arid regions with few cloudy days. Flat-plate solar thermal and photovoltaic (PV) collectors are able to use global solar radiation, which includes diffuse (scattered) and direct solar radiation. Learn more about solar radiation.

Solar thermal collectors

Low-temperature solar thermal collectors absorb the sun's heat energy to heat water for washing and bathing or for swimming pools, or to heat air inside buildings.

Concentrating collectors

Concentrating solar energy technologies use mirrors to reflect and concentrate sunlight onto receivers that absorb solar energy and convert it to heat. We can use this thermal energy for heating buildings or to produce electricity with a steam turbine or a heat engine that drives a generator.

Photovoltaic systems

Photovoltaic (PV) cells convert sunlight directly into electricity. PV systems can range from systems that provide tiny amounts of electricity for watches and calculators to systems that provide the amount of electricity that hundreds or thousands of homes use. Millions of houses and buildings around the world have PV systems on their roofs and there are many large PV power plants.

Use of solar energy

The U.S. Energy Information Administration (EIA) estimates that total solar energy use in the United States increased from about 0.06 trillion British thermal units (Btu) in 1984 to about 1,870 trillion Btu in 2022. Solar electricity generation accounted for about 97% of total solar energy use in 2022 and direct use of solar energy for space and water heating accounted for about 3%.

Total U.S. solar electricity generation increased from about 5 million kWh in 1984 (nearly all from utility-scale, solar thermal-electric power plants) to about 204 billion kWh in 2022. In 2022, utility-scale PV power plants accounted for 70% of total solar electricity generation, small-scale PV systems accounted for 29%, and utility-scale solar thermal-electric power plants accounted for 1%. Utility-scale power plants have at least 1,000 kilowatts (kW) (or one megawatt [MW]) of electricity generation capacity. Small-scale PV systems have less than one MW generation capacity.

According to EIA's International Energy Statistics, total world solar electricity generation grew from 0.4 billion kWh in 1990 to about 1.306 billion (about 1.3 trillion) kWh in 2021. The top five producers of solar electricity and their percentage shares of world total solar electricity generation in 2021 were:

Photovoltaic cells convert sunlight into electricity

A photovoltaic (PV) cell, commonly called a solar cell, is a nonmechanical device that converts sunlight directly into electricity. Some PV cells can convert artificial light into electricity.

Photons carry solar energy

Sunlight is composed of photons, or particles of solar energy. These photons contain varying amounts of energy that correspond to the different wavelengths of the solar spectrum.

A PV cell is made of semiconductor material. When photons strike a PV cell, they may reflect off the cell, pass through the cell, or be absorbed by the semiconductor material. Only the absorbed photons provide energy to generate electricity. When the semiconductor material absorbs enough sunlight (solar energy), electrons are dislodged from the material's atoms. Special treatment of the material surface during manufacturing makes the front surface of the cell more receptive to the dislodged, or free, electrons so that the electrons naturally migrate to the surface of the cell.

The flow of electricity

The movement of electrons, each carrying a negative charge, toward the front surface of the cell creates an imbalance of electrical charge between the cell's front and back surfaces. This imbalance, in turn, creates a voltage potential like the negative and positive terminals of a battery. Electrical conductors on the cell absorb the electrons. When the conductors are connected in an electrical circuit to an external load, such as a battery, electricity flows in the circuit.

The efficiency of photovoltaic systems varies by the type of photovoltaic technology

The efficiency at which PV cells convert sunlight to electricity varies by the type of cell material and technology. The efficiency of PV modules averaged less than 10% in the mid-1980s, increased to around 15% by 2015, and is now approaching 20% for state-of-the art modules. Experimental PV cells and PV cells for space satellites are nearly 50% efficient.

How photovoltaic systems operate

The PV cell is the basic building block of a PV system. Individual cells can vary in size from about 0.5 inches to about 4 inches across. However, one cell only produces 1 or 2 Watts, which is only enough electricity for small uses, such as for powering calculators or wristwatches.

PV cells are electrically connected in a packaged, weather-tight PV module or panel. PV modules vary in size and in the amount of electricity they can produce. PV module electricity generating capacity increases with the number of cells in the module or in the surface area of the module. PV modules can be connected in groups to form a PV array. A PV array can be composed of two or hundreds of PV modules. The number of PV modules connected in a PV array determines the total amount of electricity the array can generate.

Photovoltaic cells generate direct current (DC) electricity. This DC electricity can be used to charge batteries that, in turn, power devices that use direct current electricity. Nearly all electricity is supplied as alternating current (AC) in electric power lines. Devices called inverters are used on PV modules or in arrays to convert the DC electricity to AC electricity.

PV cells and modules will produce the largest amount of electricity when they are directly facing the sun. PV modules and arrays can use tracking systems that move the modules to constantly face the sun, but these systems are expensive and are mostly used in large PV power plants. Most PV systems on buildings have modules in a fixed position with the modules facing directly south (in the northern hemisphere-directly north in the southern hemisphere). Learn more about PV collector tilt angles and PV collector tracking systems.

Did you know?

Applications of photovoltaic systems

The smallest photovoltaic systems power calculators and wristwatches. Larger systems can provide electricity to pump water, to power communications equipment, to supply electricity for a single home or business, or to form large arrays that supply electricity to thousands of electricity consumers.

PV systems can supply electricity in locations where electricity distribution systems (power lines) do not exist, and they can also supply electricity to an electric power grid.

PV arrays can be installed quickly and can be any size.

The environmental effects of PV systems located on buildings is minimal.

History of photovoltaics

The first practical PV cell was developed in 1954 by Bell Telephone researchers. Beginning in the late 1950s, PV cells were used to power U.S. space satellites. By the late 1970s, PV panels were providing electricity in remote, or off-grid, locations that did not have electric power lines. Since 2004, most of the PV panels installed in the United States have been in grid-connected systems on homes, buildings, and central-station power facilities. Technical advances, lower costs for PV systems, and financial incentives and government policies have helped to greatly expand PV use since the mid-1990s. Hundreds of thousands of grid-connected PV systems are now installed in the United States.

EIA estimates that electricity generated at utility-scale PV power plants increased from 6 million kilowatthours (kWh) in 2004 to 143 billion kWh in 2022. Utility-scale power plants have at least 1,000 kilowatts (or one megawatt) of electricity generating capacity. EIA estimates that 59 billion kWh were generated by small-scale grid-connected PV systems in 2022, up from 11 billion kWh in 2014. Small-scale PV systems are systems that have less than 1,000 kilowatts of electricity generation capacity. Most small-scale PV systems are located on buildings and are sometimes called rooftop PV systems.

Solar thermal power systems use concentrated solar energy

Solar thermal power (electricity) generation systems collect and concentrate sunlight to produce the high temperature heat needed to generate electricity. All solar thermal power systems have solar energy collectors with two main components: reflectors (mirrors) that capture and focus sunlight onto a receiver. In most types of systems, a heat-transfer fluid is heated and circulated in the receiver and used to produce steam. The steam is converted into mechanical energy in a turbine, which powers a generator to produce electricity. Solar thermal power systems have tracking systems that keep sunlight focused onto the receiver during the day as the sun changes position in the sky.

Solar thermal power systems may also have a thermal energy storage system component that allows the solar collector system to heat an energy storage system during the day, and the heat from the storage system is used to produce electricity in the evening or during cloudy weather. Solar thermal power plants may also be hybrid systems that use other fuels (usually natural gas) to supplement energy from the sun during periods of low solar radiation.

Types of concentrating solar thermal power plants

Linear concentrating systems

Linear concentrating systems collect the sun's energy using long, rectangular, curved (U-shaped) mirrors. The mirrors focus sunlight onto receivers (tubes) that run the length of the mirrors. The concentrated sunlight heats a fluid flowing through the tubes. The fluid is sent to a heat exchanger to boil water in a conventional steam-turbine generator to produce electricity. There are two major types of linear concentrator systems: parabolic trough systems, where receiver tubes are positioned along the focal line of each parabolic mirror, and linear Fresnel reflector systems, where one receiver tube is above several mirrors to allow the mirrors greater mobility in tracking the sun.

A linear concentrating collector power plant has a large number, or field, of collectors in parallel rows with a north-south orientation so that the mirrors track the sun from east to west and concentrate sunlight continuously onto the receiver tubes during the day.

Parabolic troughs

Parabolic trough power plant

A parabolic trough collector has a long parabolic (curved-shaped) reflector that focuses the sun's rays on a receiver pipe located at the focus of the parabola. The collector moves to focus sunlight on the receiver as the sun moves through the sky during the day.

Because of its parabolic shape, a trough can focus the sunlight from 30 times to 100 times its normal intensity (concentration ratio) on the receiver pipe, located along the focal line of the trough, achieving operating temperatures higher than 750°F.

Parabolic trough linear concentrating systems are used in one of the longest operating solar thermal power facilities in the world, the Solar Energy Generating System (SEGS) located in the Mojave Desert in California. The facility has had nine separate plants over time, with the first plant in the system, SEGS I, operating from 1984 to 2015, and the second, SEGS II, operating from 1985 to 2015. SEGS III-VII (3-7), each with net summer electric generation capacities of 36 megawatts (MW), came online in 1986, 1987, and 1988. SEGS VIII (8) and IX (9), each with a net summer electric generation capacity of 88 MW, began operation in 1989 and 1990, respectively. SEGS 3, 4, 5, 6, 7, and 8 all ceased operation in 2021, leaving only SEGS 9 in operation as of December 31, 2021.

Solana Generating Station: a 296 MW project in Gila Bend, Arizona

Mojave Solar Project: a 275 MW project in Barstow, California

Genesis Solar Energy Project: a 250 MW project in Blythe, California

Nevada Solar One: a 69 MW plant near Boulder City, Nevada

Linear Fresnel reflectors

Linear Fresnel reflector (LFR) systems are similar to parabolic trough systems in that mirrors (reflectors) concentrate sunlight onto a receiver located above the mirrors. These reflectors use the Fresnel lens effect, which allows for a concentrating mirror with a large aperture and short focal length. These systems are capable of concentrating the sun's energy to about 30 times its normal intensity. Compact linear Fresnel reflector (CLFR)-also referred to as a concentrating linear Fresnel reflector-are a type of LFR technology with multiple absorbers within the vicinity of the mirrors. Multiple receivers allow the mirrors to change their position so they do not shade other reflectors. This improves system efficiency and reduces costs. A demonstration CLFR solar power plant was built near Bakersfield, California, in 2008, but it is currently not operating.

Solar power towers

A solar power tower system uses a large field of flat, sun-tracking mirrors called heliostats to reflect and focus sunlight onto a receiver on the top of a tower. Sunlight can be concentrated as much as 1,500 times. Some power towers use water as the heat-transfer fluid. Advanced designs are experimenting with molten nitrate salt because of its superior heat transfer and energy storage capabilities. The thermal energy-storage allows the system to produce electricity during cloudy weather or at night.

Ivanpah Solar Power Facility: a facility with three separate collector fields and towers with a combined net summer electric generation capacity of 393 MW in Ivanpah Dry Lake, California

Crescent Dunes Solar Energy Project: Crescent Dunes Solar Energy Project: a 110 MW one-tower facility with an energy storage component in Tonapah, Nevada

Solar dish/engines

Solar dish/engine systems use a mirrored dish similar to a very large satellite dish. To reduce costs, the mirrored dish usually has many small flat mirrors formed into a dish shape. The dish-shaped surface directs and focuses sunlight onto a thermal receiver, which absorbs and collects the heat and transfers it to an engine generator. The most common type of heat engine used in dish/engine systems is the Stirling engine. This system uses the fluid heated by the receiver to move pistons and create mechanical power. The mechanical power runs a generator or alternator to produce electricity.

Solar dish/engine systems always point straight at the sun and concentrate solar energy at the focal point of the dish. A solar dish's concentration ratio is much higher than linear concentrating systems, and it has a working fluid temperature higher than 1,380°F. The power-generating equipment of a solar dish can be placed at the focal point of the dish, making it well suited for remote locations, or the energy may be collected from many dishes and converted into electricity at a central point.

There are no utility-scale solar dish/engine projects in commercial operation in the United States.

Heating with the sun's energy

People use solar thermal energy to heat water and air. The two general types of solar heating systems are passive systems and active systems.

Passive solar space heating happens when the sun shines through the windows of a building and warms the interior. Building designs that use passive solar heating usually have south-facing windows that allow the sun to shine on solar heat-absorbing walls or floors during the day in the winter. The absorbed solar energy heats the building by natural radiation and convection at night. Window overhangs or shades block the sun from entering the windows during the summer to keep the building cool.

Active solar heating systems use a collector and a fluid that absorbs solar radiation. Fans or pumps circulate air or heat-absorbing liquids through collectors and then transfer the heated fluid directly to a room or to a heat storage system. Active solar water heating systems usually have a tank for storing solar heated water.

Solar collectors are either nonconcentrating or concentrating

Nonconcentrating collectors-The collector area (the area that intercepts the solar radiation) is the same as the absorber area (the area absorbing the radiation). Solar systems for heating water or air usually have nonconcentrating collectors. Flat-plate collectors are the most common type of nonconcentrating collectors for water and space heating in buildings and are used when temperatures lower than 200°F are sufficient.

A flat metal plate that intercepts and absorbs solar energy

A transparent cover that allows solar energy to pass through the cover and reduces heat loss from the absorber

A layer of insulation on the back of the absorber to reduce heat loss

Solar water heating collectors have metal tubes attached to the absorber. A heat-transfer fluid is pumped through the absorber tubes to remove heat from the absorber and transfer the heat to water in a storage tank. Solar systems for heating swimming pool water in warm climates usually do not have covers or insulation for the absorber, and pool water is circulated from the pool through the collectors and back to the pool.

Solar air heating systems use fans to move air through flat-plate collectors and into the interior of buildings.

Concentrating collectors -The area intercepting the solar radiation is greater, sometimes hundreds of times greater, than the absorber area. The collector focuses, or concentrates, solar energy onto an absorber. The collector usually moves so that it keeps sunlight focused on the absorber. Solar thermal power plants use concentrating solar collector systems because they can produce high temperature heat.

Solar energy systems/power plants do not produce air pollution, water pollution, or greenhouse gases. Using solar energy can have a positive, indirect effect on the environment when solar energy replaces or reduces the use of other energy sources that have larger effects on the environment.

Some toxic materials and chemicals are used to make the photovoltaic (PV) cells that convert sunlight into electricity. Some solar thermal systems use potentially hazardous fluids to transfer heat. Leaks of these materials could be harmful to the environment. U.S. environmental laws regulate the use and disposal of these types of materials.

As with any type of power plant, large solar power plants can affect the environment near their locations. Clearing land for construction and the placement of the power plant may have long-term effects on the habitats of native plants and animals. Some solar power plants may require water for cleaning solar collectors and concentrators or for cooling turbine generators. Using large volumes of ground water or surface water in some arid locations may affect the ecosystems that depend on these water resources. In addition, the beam of concentrated sunlight a solar power tower creates can kill birds and insects that fly into the beam.

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The sun has produced energy for billions of years and is the ultimate source for all of the energy sources and fuels that we use today. People have used the sun's rays (solar radiation) for thousands of years for warmth and to dry meat, fruit, and grains.

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In this video from NOVA’s Energy Lab, learn about the benefits and limitations of converting the Sun’s light and heat into electricity. Animations show how two solar power technologies—photovoltaic cells and concentrated solar power systems—convert the Sun’s energy into electrical energy. Solar power technologies are environmentally friendly, but there are technological challenges that limit their widespread use. For example, solar power technologies are not very efficient, they are relatively expensive, and we do not yet have a good way to store solar energy.
This video is available in both English and Spanish audio, along with corresponding closed captions.

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Wind is a clean and inexhaustible source of energy that can be harnessed to produce power. Historically, wind power in the form of windmills has been used for centuries for such tasks as grinding grain and pumping water. Today sophisticated wind machines known as wind turbines are used in many parts of the world to convert the kinetic energy of wind to electric power.

Modern commercial wind turbines produce electricity by using rotational energy to drive a generator. These turbines are made up of a blade or rotor and an enclosure called a nacelle that contains a drive train atop a tall tower. Large wind turbines (producing up to 1.8 megawatts of power) can have a blade length of over 130 feet (40 meters) and be placed on towers some 260 feet (about 80 meters) tall. Smaller turbines can be used to provide power to individual homes. Wind farms are areas where a number of wind turbines are grouped together, providing a larger total energy source.

Wind resources are calculated based on the average wind speed and the distribution of wind speed values occurring within a particular area. Areas are grouped into wind power classes that range from 1 to 7. A wind power class of 3 or above (equivalent to a wind power density of 150-200 watts per square meter or a mean wind of 11.5-12.5 miles per hour [5.1-5.6 meters per second] at a height of 33 feet [10 meters] above ground) is suitable for utility-scale wind power generation, although some suitable sites may also be found in areas of classes 1 and 2. In the United States there are substantial wind resources in the Great Plains region as well as in some offshore locations. As of 2009 the largest wind farm in the world was the 100,000-acre (40,470-hectare) Roscoe Wind Complex in Texas, which employed 627 wind turbines to produce 781.5 megawatts. By comparison, a typical new coal-fired generating plant averages about 550 megawatts.

By the early 21st century, wind was contributing slightly more than 1 percent of the world's total electricity, and electricity generation by wind has been increasing dramatically because of concerns over the cost of petroleum and the effects of fossil fuel combustion on the climate and environment. From 2004 to 2009, for example, total wind power increased from 47,693 to 159,213 megawatts worldwide. By 2009 the United States possessed the most installed wind capacity (35,159 megawatts), followed by China (26,010) and Germany (25,777), while Denmark generated the largest percentage of its electricity from wind (20 percent). The wind power industry estimates that the world could feasibly generate 12 percent of its total electricity from wind power by 2020. Various estimates put the cost of wind energy between 3 and 12 cents per kilowatt-hour, depending on the location. This is comparable to the cost of fossil energy. (The cost of coal-generated electricity is estimated at 4-8 cents per kilowatt-hour.)

Challenges to the large-scale implementation of wind energy include siting requirements such as wind availability, aesthetic and environmental concerns, and land availability. Wind farms are most cost-effective in areas with consistent strong winds; however, these areas are not necessarily near large population centers. Thus, power lines and other components of electrical distribution systems must have the capacity to transmit this electricity to consumers. In addition, since wind is an intermittent and inconsistent power source, storing power may be necessary. Public advocacy groups have raised concerns about the potential disruptions that wind farms may have on wildlife and overall aesthetics. For example, the first proposed offshore wind farm in the United States, the Cape Wind Project located off the coast of Cape Cod in Massachusetts, was strongly opposed by residents concerned about the natural landscape. (In April 2010, following nine years of regulatory review of the Cape Wind Project, the U.S. Department of the Interior announced its approval for the wind farm to be built.) In addition, wind generators have been blamed for injuring and killing birds; however, experts have shown that modern turbines have a small effect on bird populations. The National Audubon Society, a large environmental group based in the United States and focused on the conservation of birds and other wildlife, is strongly in favor of wind power, provided that wind farms are appropriately sited to minimize the impacts on migrating bird populations and important wildlife habitat.

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Wind is a clean and inexhaustible source of energy that can be harnessed to produce power. Historically, wind power in the form of windmills has been used for centuries for...

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Energy from moving air

Wind is caused by uneven heating of the earth's surface by the sun. Because the earth's surface is made up of different types of land and water, it absorbs the sun's heat at different rates. One example of this uneven heating is the daily wind cycle.

The daily wind cycle

During the day, air above the land heats up faster than air over water. Warm air over land expands and rises, and heavier, cooler air rushes in to take its place, creating wind. At night, the winds are reversed because air cools more rapidly over land than it does over water.

In the same way, the atmospheric winds that circle the earth are created because the land near the earth's equator is hotter than the land near the North Pole and the South Pole.

Wind energy for electricity generation

Today, wind energy is mainly used to generate electricity. Water-pumping windmills were once used throughout the United States and some still operate on farms and ranches, mainly to supply water for livestock.

How wind turbines work

Wind turbines use blades to collect the wind's kinetic energy. Wind flows over the blades creating lift (similar to the effect on airplane wings), which causes the blades to turn. The blades are connected to a drive shaft that turns an electric generator, which produces the electricity.

Electricity generation with wind

Total annual U.S. electricity generation from wind energy increased from about 6 billion kilowatthours (kWh) in 2000 to about 435 billion kWh in 2022. In 2022, wind turbines were the source of about 10.2% of total U.S. utility-scale electricity generation. Utility scale includes facilities with at least one megawatt (1,000 kilowatts) of electricity generation capacity

New technologies have decreased the cost of producing electricity from wind, and growth in wind power has been encouraged by government and industry incentives.

Wind power plants require careful planning

Operating a wind power plant is more complex than simply erecting wind turbines in a windy area. Wind power plant owners must carefully plan where to position wind turbines and must consider how fast and how often the wind blows at the site.

Good places for wind turbines are where the annual average wind speed is at least 9 miles per hour (mph)-or 4 meters per second (m/s)-for small wind turbines and 13 mph (5.8 m/s) for utility-scale turbines. Favorable sites include the tops of smooth, rounded hills; open plains and water; and mountain gaps that funnel and intensify wind. Wind resources are generally more favorable for electricity generation at higher elevations above the earth's surface. Large wind turbines are placed on towers that range from about 500 feet to as much as 900 feet tall.

Wind speeds are not the same across the country

Wind energy resources vary hourly and seasonally throughout the United States. For example, in Tehachapi, California, where numerous wind turbines are located, the wind blows more frequently from April through October than it does in the winter, and the wind is usually strongest in the afternoon. These fluctuations are a result of the extreme heat of the Mojave Desert during summer months. As the hot air over the desert rises, the cooler, denser air above the Pacific Ocean rushes through the Tehachapi mountain pass to take its place. In Montana, strong winter winds channeled through Rocky Mountain valleys create more intense winds during the winter.

Fortunately, the seasonal variations in wind speeds in California and Montana match the electricity demands of consumers in those states. In California, people use more electricity in the afternoon and during the summer. In Montana, people use more electricity, in general, during the winter.

Locations of U.S. wind power projects

In 2022, 42 states had utility-scale wind power projects, which together produced about 10% (435 billion kilowatthours [kWh]) of total U.S. utility-scale electricity generation. ¹ The five states with the most electricity generation from wind in 2022 were Texas, Iowa, Oklahoma, Kansas, and Illinois. These states combined produced about 57% of total U.S. wind electricity generation in 2022

International wind power

World wind electricity generation has also increased substantially in recent years. In 1990, 16 countries generated a total of about 3.6 billion kWh of wind electricity. In 2010, 105 countries generated about 340 billion kWh, and in 2020, 129 countries (includes Puerto Rico) generated about 1,597 billion kWh of wind electricity

Offshore wind power

The waters off the coasts of the United States have significant potential for electricity generation from wind energy. There are currently two operating U.S. offshore wind energy projects: the Block Island wind farm off the coast of Rhode Island, with 30 megawatts (MW) of electricity generation capacity, and the Coastal Virginia Offshore Wind pilot project with 12 MW electricity generation capacity. As of December 2022, wind project developers reported plans for about 7,500 MW of nameplate wind electricity generation capacity in waters off the coasts of Maryland, Massachusetts, New Jersey, Rhode Island, and Virgina, and about 20 MW in Ohio state waters on Lake Erie. European countries and China lead the world in offshore wind electric generation capacity. Many other countries have and are developing offshore wind energy projects.

Horizontal-axis turbines

Vertical-axis turbines

The size of wind turbines varies widely. The length of the blades is the biggest factor in determining the amount of electricity a wind turbine can generate. Small wind turbines that can power a single home may have an electricity generating capacity of 10 kilowatts (kW). The largest wind turbines in operation have electricity generating capacities of around 15,000 kW, and larger turbines are in development. Large turbines are often grouped together to create wind power plants, or wind farms, that provide power to electricity grids.

Horizontal-axis turbines are similar to propeller airplane engines

Horizontal-axis turbines have blades like airplane propellers, and they commonly have three blades. The largest horizontal-axis turbines are as tall as 20-story buildings and have blades more than 100 feet long. Taller turbines with longer blades generate more electricity. Nearly all of the wind turbines currently in use are horizontal-axis turbines.

Vertical-axis turbines look like egg beaters

Vertical-axis turbines have blades that are attached to the top and the bottom of a vertical rotor. The most common type of vertical-axis turbine-the Darrieus wind turbine, named after the French engineer Georges Darrieus who patented the design in 1931-looks like a giant, two-bladed egg beater. Some versions of the vertical-axis turbine are 100 feet tall and 50 feet wide. Very few vertical-axis wind turbines are in use today because they do not perform as well as horizontal-axis turbines.

Wind power plants, or wind farms, produce electricity

Wind power plants, or wind farms, are clusters of wind turbines that produce large amounts of electricity. A wind farm usually has many turbines scattered over a large area. One of the United States' largest wind farms is the Horse Hollow Wind Energy Center in Texas, which at the end of 2021, had 422 wind turbines spread over about 47,000 acres. The project has a combined electricity generating capacity of about 735 megawatts (or 735,000 kilowatts).

People have been using wind energy for thousands of years

People used wind energy to propel boats along the Nile River as early as 5,000 BC. By 200 BC, simple wind-powered water pumps were used in China, and windmills with woven-reed blades were grinding grain in Persia and the Middle East.

New ways to use wind energy eventually spread around the world. By the 11th century, people in the Middle East were using windpumps and windmills extensively for food production. Merchants and the Crusaders brought wind technology to Europe. The Dutch developed large windpumps to drain lakes and marshes in the Rhine River Delta. Immigrants from Europe eventually took wind energy technology to the Western Hemisphere.

American colonists used windmills to grind grain, to pump water, and to cut wood at sawmills. Homesteaders and ranchers installed thousands of windpumps as they settled the western United States. In the late 1800s and early 1900s, small wind-electric generators (turbines) were also widely used.

When power lines were built to transmit electricity to rural areas in the 1930s, wind pump and small turbine use began to decline. However, some ranches still use windpumps to supply water for livestock. Small wind turbines are becoming more common again, mainly to supply electricity in remote and rural areas.

Wind energy use expanded in the wake of oil shortages and environmental concerns

The oil shortages of the 1970s changed the energy environment for the United States and the world. The oil shortages created an interest in developing ways to use alternative energy sources, such as wind energy, to generate electricity. The U.S. federal government supported research and development of large wind turbines. In the early 1980s, thousands of wind turbines were installed in California, largely because of federal and state policies that encouraged the use of renewable energy sources.

In the 1990s and 2000s, the U.S. federal government established incentives to use renewable energy sources in response to a renewed concern for the environment. The federal government also provided research and development funding to help reduce the cost of wind turbines and offered tax and investment incentives for wind power projects. In addition, state governments enacted new requirements for electricity generation from renewable sources, and electric power marketers and utilities began to offer electricity generated from wind and other renewable energy sources (sometimes called green power) to their customers. These policies and programs resulted in an increase in the number of wind turbines and in the amount of electricity generated from wind energy.

The share of total U.S. electricity generation from wind energy has grown from less than 1% in 1990 to about 10.2% in 2022. Financial and other incentives for electricity generation with wind energy have resulted in a large expansion of wind energy use in the United States and Europe. China has invested heavily in wind energy and is now the world's largest wind electricity generator. In 1990, 16 countries generated a total of about 3.6 billion kWh of wind electricity. In 2021, at least 128 countries (including Puerto Rico) generated about 1,808 billion kWh of wind electricity.

Wind is an emissions-free source of energy

Wind is a renewable energy source. Overall, using wind to produce energy has fewer effects on the environment than many other energy sources. Wind turbines do not release emissions that can pollute the air or water (with rare exceptions), and they do not require water for cooling. Wind turbines may also reduce the amount of electricity generation from fossil fuels, which results in lower total air pollution and carbon dioxide emissions.

An individual wind turbine has a relatively small physical footprint. Groups of wind turbines, sometimes called wind farms, are located on open land, on mountain ridges, or offshore in lakes or the ocean.

Wind turbines have effects on the environment

Modern wind turbines can be very large machines, and they may visually affect the landscape. A small number of wind turbines have also caught fire, and some have leaked lubricating fluids, but these occurrences are rare. Some people do not like the sound that wind turbine blades make as they turn in the wind. Some types of wind turbines and wind projects cause bird and bat deaths. These deaths may contribute to declines in the population of species also affected by other human-related impacts. The wind energy industry and the U.S. government are researching ways to reduce the effect of wind turbines on birds and bats.

Most wind power projects on land require service roads that add to the physical effects on the environment. Producing the metals and other materials used to make wind turbine components has impacts on the environment, and fossil fuels may have been used to produce the materials. Although most of the materials used to make wind turbines can be reused or recycled, turbine blades, as most are currently constructed, cannot be recycled. Researchers at the National Renewable Energy Laboratory (NREL) established an approach to manufacturing wind turbine blades, employing a thermoplastic resin system. These thermoplastic resins enable a manufacturing process that allows wind turbine blades to be recycled at their end of life and also reduces the energy required to manufacture blades.

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Wind is caused by uneven heating of the earth's surface by the sun. Because the earth's surface is made up of different types of land and water, it absorbs the sun's heat at different rates. One example of this uneven heating is the daily wind cycle.

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How do wind turbines work? - Rebecca J. Barthelmie and Sara C. Pryor

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Advantages and Challenges of Wind Energy 

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Advantages and Challenges of Wind Energy 

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Advantages and Challenges of Wind Energy

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Wind energy advantages explain why wind power is one of the fast-growing renewable energy sources in all the world.

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Disadvantages of Solar Energy

The disadvantages of solar energy are becoming fewer as the industry advances and grows, creating economies of scale. Technological advances are helping solar go mainstream. Here are how the disadvantages of solar energy and the pros and cons stack up.

1. The high initial costs of installing panels

The most commonly cited solar energy disadvantage, cost, is declining as the industry expands. The initial cost to buy and install the equipment is not cheap. Still, if cost is an issue, leasing options may reduce the amount of your initial outlay. If you do choose to buy, you will need to live in your home for a number of years before the system pays for itself. It's a long-term investment better suited to property owners than renters.

2. Solar energy storage is expensive

Of the disadvantages of solar energy, the temporary decline in energy production during bad weather has been a major issue. Days with low solar energy, however, are having less of an effect due to advances in battery technology. Old technology for storing solar energy, like lead acid batteries are being replaced by alternatives. Lithium ion batteries offer greater power at a lower cost. Nickel-based batteries have an extremely long life. New technologies, like flow batteries, promise scale and durable power storage.

3. Solar doesn't work for every roof type

Not every room will work well with solar panels. Orientation matters. If your roof doesn't face the sun, you won't be able to capture enough solar energy. Roofs that angle into the sun tend to work better than flat roofs.

Roofing materials like asphalt shingles, metal and tiles make installing solar panels easier. If your room is made with other materials, installation may be more expensive. Part of what makes energy-efficient roofs is their ability to support solar panels.

4. Solar panels are dependent on sunlight

It's obvious that solar panels need sunlight to generate electricity. They won't produce electricity at night when you need it for light and they can be inefficient during storms and gloomy days. Your solar energy system needs batteries if you plan to fully depend on solar energy to power your home.

Batteries are one of the more expensive components of your system. Unlike solar panels, they do wear out and need careful maintenance to lengthen their lives. Comparing wind power vs. solar power, wind will keep generating electricity at night and during storms, as long as there is enough wind. Many people use both in residential systems.

Constellation Energy and Solar Energy

When weighing the pros and cons of solar energy for your home, there are additional options worth considering. Community solar projects are a great way to get the advantages of solar energy without buying and maintaining a system yourself.

If your home and roof won't support solar panels or if you don't have enough money to invest in one, community solar might be your answer. With this option, you agree to participating in a program that allows you receive credits for every kWh generated by the solar facility. You get a credit on your electricity bill proportional to your percentage of ownership in the project's energy.

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The Advantages and Disadvantages of Solar Energy

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Solar is a renewable energy source that can power your home, reduce your electric costs and maybe even earn you money back. Learn the pros & cons of solar energy here.

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What is biomass? Where does it come from? How are biofuels made? What is bioenergy? Browse through our informational resources to learn more.

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Over the years, biomass has become a popular alternative energy source. In fact, biomass has a lot of potential to be a reliable source of renewable energy to power our society.

However, just like any energy resource, it comes with both its benefits and drawbacks.

We're going to take a look at some key pros and cons of biomass energy, and what we can expect from biomass in the future.

What are the pros and cons of biomass energy?

When looking at renewable energy sources, it's important to look at all of their advantages and disadvantages. The following table outlines some of the biggest pros and cons of biomass energy:

What is biomass energy?

Biomass is organic matter that comes from plants and animals. Organic waste such as wood, crop waste, animal waste, food waste, yard waste, and wood waste can all be used as sources of biomass energy.

Biomass can be used as a source of energy in two ways:

Burning organic materials directly to create heat

Converting biomass into a liquid biofuel that can then be burned for energy

Liquid biofuels, like biodiesel and biogas, are usually used as a fuel source to help meet transportation needs.

When biomass is burned directly, it is used to create steam, which turns a turbine to create electricity. In this article, we'll focus mostly on biomass energy that creates electricity, not biofuels.

Advantages of biomass energy

1. Renewable

Biomass energy is a renewable form of energy. As we use biomass materials, the supply of organic matter is diminishing. However, biomass can be regenerated quickly.

The fact that the biomass supply can be regenerated within a human lifetime is what makes biomass renewable.

2. Reliable

Biomass is a reliable resource that can produce energy at any time. This is an advantage over other renewable energy resources, like wind and solar energy, which are intermittent.

When the wind isn't blowing, no wind energy is being created by turbines. This means you can't rely on wind to produce electricity whenever you need it. Unless, of course, the wind turbine is paired with battery storage.

Bioenergy power plants on the other hand, can be turned on and off at any time to meet energy demand. As long as there is biomass material available, electricity can be produced.

3. Abundant

One of the biggest pros of biomass energy is that biomass is abundant. There is a growing amount of organic material being produced every day; you can find biomass nearly everywhere on the planet. This means that biomass won't have the issue of limited availability, like fossil fuels do.

However, biomass does need to be responsibly managed in order to keep its abundant supply well-stocked. If we overuse the biomass that is available, we could run into availability issues while we wait to replenish the supply.

4. Waste reduction

One reason why biomass is so widely available is because the planet produces a lot of waste. Much of the waste we make is biodegradable, like food and plant waste. Instead of letting it become garbage, we could instead turn it into electricity!

Biomass energy takes waste that would otherwise sit in a landfill and makes it useful. This reduces the amount of waste that goes into landfills, which is better for the environment.

Plus, with less waste, we would need fewer and smaller landfills. This opens up more land that can be used by communities.

5. Carbon-neutral

Carbon dioxide emissions are driving forces of climate change. Biomass is considered a carbon-neutral energy source because it fits into the natural carbon cycle, which traditional fossil fuels do not.

There is carbon dioxide that is released into the atmosphere when biomass energy is produced. But, this is the same amount of carbon dioxide that was absorbed by the plants during their lifecycle. So, when biomass is burned it does not release any 'new' carbon emissions into the atmosphere.

Then, when new plants grow, they absorb carbon dioxide back out of the atmosphere, and enter the cycle again.

Disadvantages of biomass energy

1. Expensive

The production of biomass energy can come with a high price tag. First, constructing biomass energy plants requires a significant upfront investment. Then, the cost of harvesting and transporting biomass materials needs to be considered.

Plus, the organic material needs to be stored when it gets to the plant, which requires even more money. All of this makes biomass more expensive than other renewable options on the market.

Other renewable resources, like solar, don't require these regular transportation and storage costs. Once a solar farm is built, there is no need to transport fuel or to store sunlight anywhere.

Even though biomass is more expensive than other renewables, it is still cheaper than fossil fuels. It costs much less to harvest biomass than it does to mine and extract fossil fuels.

2. Requires space

Biomass energy plants need quite a bit of space, mainly because of needing storage space. This limits where biomass energy plants can be built.

Some biomass plants also grow their own organic material. These plants may need large amounts of space to be able to grow crops or small forests. Biomass energy plants that grow their own fuel use more land-per-kilowatt hour of electricity produced.

3. Greenhouse gas emissions

As we said, biomass energy is carbon-neutral. However, biomass is still releasing carbon dioxide into the atmosphere. Other renewable sources are carbon-zero, which is much better when looking to tackle climate change. The less carbon dioxide being released - the better.

Carbon isn't the only thing being released into the atmosphere from biomass energy. Burning wood and other biomass fuels releases many other greenhouse gases, most notably nitrogen oxides, carbon monoxide, and methane.

Methane gas is a significant contributor to air pollution and climate change, as it traps about 30 times more heat than carbon dioxide.

4. Environmental impact

Although biomass energy is renewable, it isn't the most environmentally friendly renewable option out there.

Relying on biomass energy could lead to devastating deforestation. As biomass plants require more materials, forests could get cut down at faster rates. It may also encourage monocultures of crops, which decreases biodiversity and strips soils of nutrients, making areas more susceptible to erosion.

Some biomass plants rely on algae, which tend to require large amounts of phosphorus fertilizers to produce the amounts needed for energy production. Overusing fertilizers can cause serious damage to local waterways and to wildlife, most notably birds.

Even using plants for biomass energy could increase the amount of fertilizers and pesticides being used and negatively impact the surrounding ecosystem.

5. Inefficient

Right now, biomass energy is not as efficient as other energy sources. In many cases, it takes more energy to burn the organic material than the process actually produces.

New technologies will need to emerge to make biomass more efficient if we want to use it on a large scale.

The future of biomass energy

There is no doubt that biomass energy is one of the few options for replacing fossil fuels.

If new technologies are developed to make the process more efficient, the use of biomass energy has serious potential. For now, it comes with a big set of drawbacks that make it difficult for it to be widely implemented.

If you're looking for a way to use the power of renewable and clean energy, you should consider making the switch to solar. Not only do solar panels decrease your carbon footprint, they can eliminate your electric bill!

Use our solar panel calculator to find out how much you can save when you power your home with solar.

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Over the years, biomass has become a popular alternative energy source. In fact, biomass has a lot of potential to be a reliable source of renewable energy to power our society. However, just like any energy resource, it comes with both its benefits and drawbacks.

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Biomass-renewable energy from plants and animals

Biomass is renewable organic material that comes from plants and animals. Biomass was the largest source of total annual U.S. energy consumption until the mid-1800s. Biomass continues to be an important fuel in many countries, especially for cooking and heating in developing countries. The use of biomass fuels for transportation and for electricity generation is increasing in many developed countries as a means of avoiding carbon dioxide emissions from fossil fuel use. In 2022, biomass provided nearly 5% of total primary energy use in the United States.

Biomass contains stored chemical energy from the sun. Plants produce biomass through photosynthesis. Biomass can be burned directly for heat or converted to renewable liquid and gaseous fuels through various processes.

Biomass sources for energy include

Wood and wood processing wastes-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, and algae, and crop and food processing residues

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

Animal manure and human sewage

Converting biomass to energy

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 industrial process heat, and for generating electricity in steam turbines.

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

Pyrolysis entails heating organic materials to 800-900oF (400-500 oC) in the near 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 1,400-1700oF (800-900oC) with injections of controlled amounts of free oxygen and/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), which are used to produce biodiesel.

Biological conversion includes fermentation to convert biomass into ethanol and anaerobic digestion to produce renewable natural gas. Ethanol is used as a vehicle fuel. Renewable natural gas-also called biogas or biomethane -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 total U.S. primary energy consumption, equal to about 4,930 trillion British thermal units (TBtu) (or 4.9 quadrillion Btu). 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 account for the largest amounts, in terms of energy content, and largest percentage shares of total annual U.S. biomass consumption. 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. Liquid biofuels (ethanol and biomass-based diesel) account for most of the transportation sector's biomass consumption.

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 product in recent years. In 2022, the United States exported about 8.8 million tons of wood fuel pellets (Table 8).

Biomass-Wood and wood waste

People have used wood for cooking, heating, and lighting for thousands of years. Wood was the main source of energy for the United States and the rest of the world until the mid-1800s. Wood continues to be an important fuel in many countries, especially for cooking and heating in developing countries.

In 2022, about 2.1% of total U.S. annual energy consumption was from wood and wood waste-bark, sawdust, wood chips, wood scrap, and paper mill residues.

Using wood and wood waste

Industry accounts for most wood and wood-waste fuel consumption in the United States. The top industrial users are wood product and paper manufacturers. They use lumber mill and paper mill waste to produce steam and electricity, which saves money because it reduces the amount of other fuels and electricity they must purchase to operate their facilities. In 2022, the industrial sector accounted for about 61% of total U.S. consumption of wood and wood waste. Wood and wood waste also accounted for about 8.5% of industrial sector end-use energy consumption and 6.9% of total industrial sector energy consumption. ¹

The residential sector is the second-largest user of wood for energy in United States. Wood is used in homes throughout the United States for heating as cord wood in fireplaces and wood-burning appliances, and as pellets in pellet stoves. wood energy accounted for about 4.0% of residential sector end-use energy consumption and 2.5% of total residential energy consumption. In 2020, 8.9% of all U.S households (about 11 million) used wood for energy (mostly for space heating). About 2.2 million households used wood as the main space-heating fuel.

In the electric power sector, there are several power plants that burn mostly wood to generate electricity, and some coal-burning power plants burn wood chips with coal to reduce sulfur dioxide emissions. Most of the commercial sector's use of wood is for heating.

Energy from municipal solid waste

Biomass, or biogenic (plant or animal products), materials such as paper, cardboard, food waste, grass clippings, leaves, wood, and leather products

Nonbiomass combustible materials such as plastics and other synthetic materials made from petroleum

Noncombustible materials such as glass and metals

In 2018, about 12% of the 292 million tons of MSW produced in the United States was burned in waste-to-energy plants.

Waste-to-energy plants make steam and electricity

MSW is usually burned at special waste-to-energy plants that use the heat from the fire to make steam for generating electricity or to heat buildings. In 2020, 65 U.S. power plants generated about 13.5 billion kilowatthours of electricity from burning nearly 25 million tons of combustible MSW. Biomass materials accounted for about 61% of the weight of the combustible MSW and for about 45% of the electricity generated in waste-to-energy plants. The remainder of the combustible MSW was nonbiomass combustible material, mainly plastics.

Read about a field trip to a real waste-to-energy plant or learn about the history of MSW.

Many large landfills also generate electricity by using the methane gas that is produced from decomposing biomass in landfills.

Waste-to-energy is a waste management option

Producing electricity is only one reason to burn MSW. Burning waste also reduces the amount of material that would probably be buried in landfills. Burning MSW reduces the volume of waste by about 87%.

Biogas (or renewable natural gas) from biomass

Biogas, which may be called renewable natural gas, is produced from biomass through the process of anaerobic decomposition. Anaerobic bacteria-bacteria that live without the presence of free oxygen-occur naturally in soils, in water bodies such as swamps and lakes, and in the digestive tracts of humans and animals. These bacteria eat and break down, or digest, biomass and produce biogas. Biogas is composed mostly of methane (CH ₄) and carbon dioxide (CO ₂). Methane is the same energy-rich compound found in natural gas. The composition of biogas varies from 40%-60% methane to 60%-40% CO ₂, with small amounts of water vapor and other gases.

Biogas forms in, and can be collected from, municipal-solid-waste landfills and livestock manure holding ponds. Biogas can also be produced under controlled conditions in special tanks called anaerobic digesters. Biogas can be treated to remove CO ₂ and other gases, and it can be used as a fuel just like natural gas. The material that is left after anaerobic digestion is complete is called digestate, which is rich in nutrients and can be used as a fertilizer.

Collecting and using biogas from landfills

Landfills for municipal solid waste are a source of biogas. Biogas is produced naturally by anaerobic bacteria in municipal-solid-waste landfills and is called landfill gas. Landfill gas with a high methane content can be dangerous to people and the environment because methane is flammable. Methane is also a strong greenhouse gas. Biogas contains small amounts of hydrogen sulfide, a noxious and potentially toxic compound when in high concentrations.

In the United States, regulations under the Clean Air Act require municipal-solid-waste landfills of a certain size to install and operate a landfill gas collection and control system. Some landfills reduce landfill gas emissions by capturing and burning-or flaring-the landfill gas. Burning the methane in landfill gas produces CO ₂, but CO ₂ is not as strong a greenhouse gas as methane. Many landfills collect landfill gas, treat it to remove CO ₂, water vapor, and hydrogen sulfide, and then sell the methane. Some landfills use the methane gas to generate electricity.

The U.S. Energy Information Administration (EIA) estimates that in 2020 about 256 billion cubic feet (Bcf) of landfill gas was collected at 327 U.S. landfills and burned to generate about 10 billion kilowatthours (kWh) of electricity, or about 0.3% of total U.S. utility-scale electricity generation in 2020

Biogas from sewage and industrial wastewater treatment

Many municipal sewage treatment plants and manufacturers such as paper mills and food processors use anaerobic digesters as part of their waste treatment processes. Some sewage treatment and industrial facilities collect and use the biogas produced in anaerobic digesters to heat the digesters, which enhances the anaerobic digestion process and destroys pathogens, and some use it to generate electricity to use at the facility or to sell. EIA estimates that in 2020, about 61 of these types of waste treatment facilities in the United States produced a total of about 1 billion kWh of electricity.

Using biogas from animal waste

Some dairy farms and livestock operations use anaerobic digesters to produce biogas from manure and used bedding material from their barns. Some livestock farmers cover their manure holding ponds (also called manure lagoons) to capture biogas that forms in the lagoons. The methane in the biogas can be burned to heat water and buildings and as fuel in diesel-engine generators to generate electricity for the farm. EIA estimates that in 2020, 20 large dairies and livestock operations in the United States produced a total of about 173 million kWh (or 0.17 billion kWh) of electricity from biogas.

Using biomass for energy has positive and negative effects

Biomass and biofuels made from biomass are alternative energy sources to fossil fuels-coal, petroleum, and natural gas. Burning either fossil fuels or biomass releases carbon dioxide (CO ₂), a greenhouse gas. However, the plants that are the source of biomass capture a nearly equivalent amount of CO ₂ through photosynthesis while they are growing, which can make biomass a carbon-neutral energy source.

Burning wood

Using wood, wood pellets, and charcoal for heating and cooking can replace fossil fuels and may result in lower CO ₂ emissions overall. Wood can be harvested from forests, from woodlots that have to be thinned, or from urban trees that fall down or have to be cut down.

Wood smoke contains harmful pollutants such as carbon monoxide and particulate matter. Modern wood-burning stoves, pellet stoves, and fireplace inserts can reduce the amount of particulates from burning wood. Wood and charcoal are major cooking and heating fuels in poor countries, but if people harvest the wood faster than trees can grow, it causes deforestation. Planting fast-growing trees for fuel and using fuel-efficient cooking stoves can help slow deforestation and improve the environment.

Burning municipal solid waste (MSW) or wood waste

Burning municipal solid waste (MSW, or garbage) in waste-to-energy plants could result in less waste buried in landfills. On the other hand, burning garbage produces air pollution and releases the chemicals and substances in the waste into the air. Some of these chemicals can be hazardous to people and the environment if they are not properly controlled.

The U.S. Environmental Protection Agency (EPA) applies strict environmental rules to waste-to-energy plants, which require waste-to-energy plants to use air pollution control devices such as scrubbers, fabric filters, and electrostatic precipitators to capture air pollutants.

Scrubbers clean emissions from waste-to-energy facilities by spraying a liquid into the combustion gases to neutralize the acids present in the stream of emissions. Fabric filters and electrostatic precipitators also remove particles from the combustion gases. The particles-called fly ash-are then mixed with the ash that is removed from the bottom of the waste-to-energy furnace.

A waste-to-energy furnace burns at high temperatures (1,800°F to 2,000°F), which breaks down the chemicals in MSW into simpler, less harmful compounds.

Disposing ash from waste-to-energy plants

Ash from waste-to-energy plants can contain high concentrations of various metals that were present in the original waste. Textile dyes, printing inks, and ceramics, for example, may contain lead and cadmium.

Separating waste before burning can solve part of the problem. Because batteries are the largest source of lead and cadmium in municipal waste, they should not be included in regular trash. Florescent light bulbs should also not be put in regular trash because they contain small amounts of mercury.

The EPA tests ash from waste-to-energy plants to make sure that it is not hazardous. The test looks for chemicals and metals that could contaminate ground water. Some MSW landfills use ash that is considered safe as a cover layer for their landfills, and some MSW ash is used to make concrete blocks and bricks.

Collecting landfill gas or biogas

Biogas forms as a result of biological processes in sewage treatment plants, waste landfills, and livestock manure management systems. Biogas is composed mainly of methane (a greenhouse gas) and CO ₂. Many facilities that produce biogas capture it and burn the methane for heat or to generate electricity. This electricity is considered renewable and, in many states, contributes to meeting state renewable portfolio standards (RPS). This electricity may replace electricity generation from fossil fuels and can result in a net reduction in CO ₂ emissions. Burning methane produces CO ₂, but because methane is a stronger greenhouse gas than CO ₂, the overall greenhouse effect is lower.

Liquid biofuels: ethanol and biodiesel

Biofuels are transportation fuels such as ethanol and biodiesel. The federal government promotes biofuels as transportation fuels to help reduce oil imports and CO ₂ emissions. In 2007, the U.S. government set a target to use 36 billion gallons of biofuels by 2022. As a result, nearly all gasoline now sold in the United States contains some ethanol.

Biofuels may be carbon-neutral because the plants that are used to make biofuels (such as corn and sugarcane for ethanol and soy beans and oil palm trees for biodiesel) absorb CO ₂ as they grow and may offset the CO ₂ emissions when biofuels are produced and burned.

Growing plants for biofuels is controversial because the land, fertilizers, and energy for growing biofuel crops could be used to grow food crops instead. In some parts of the world, large areas of natural vegetation and forests have been cut down to grow sugar cane for ethanol and soybeans and oil palm trees for biodiesel. The U.S. government supports efforts to develop alternative sources of biomass that do not compete with food crops and that use less fertilizer and pesticides than corn and sugar cane. The U.S. government also supports methods to produce ethanol that require less energy than conventional fermentation. Ethanol can also be made from waste paper, and biodiesel can be made from waste grease and oils and even algae.

Ethanol and gasoline-ethanol blends burn cleaner and have higher octane ratings than pure gasoline, but they have higher evaporative emissions from fuel tanks and dispensing equipment. These evaporative emissions contribute to the formation of harmful, ground-level ozone and smog. Gasoline requires extra processing to reduce evaporative emissions before it is blended with ethanol. Biodiesel combustion produces fewer sulfur oxides, less particulate matter, less carbon monoxide, and fewer unburned and other hydrocarbons, but it does produce more nitrogen oxide than petroleum diesel.

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Biomass is renewable organic material that comes from plants and animals. Biomass was the largest source of total annual U.S. energy consumption until the mid-1800s. Biomass continues to be an important fuel in many countries, especially for cooking and heating in developing countries.

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Green Mountain Energy: How does BioEnergy work

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Green Mountain Energy: How does BioEnergy work

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Renewable Energy 101: How Does Biomass Energy Work?

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Hydroelectric power | Definition, Renewable, Advantages, Disadvantages, & Facts

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Hydroelectric power, electricity produced from generators driven by turbines that convert the potential energy of moving water into mechanical energy. Hydroelectric power plants usually are located in dams that impound rivers, though tidal action is used in some coastal areas.

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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 is usually the largest single renewable energy source of annual electricity generation in the United States.

n 2022, hydroelectricity accounted for about 6.2% of total U.S. utility-scale electricity generation and 28.7% of total utility-scale renewable electricity generation. ¹ 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

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

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

3. 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 and long-term changes in rain and snowfall, such as droughts, have a big effect on 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) 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 fall, the more electricity a hydropower plant can produce. A big river, such as the Columbia River that forms the border between Oregon and Washington, carries a great deal of energy in its flow. Water descending rapidly from a high point, such as Niagara Falls in New York, also has substantial energy in its flow.

At hydropower plants, water flows through a pipe, or penstock, then pushes against and turns blades in a turbine to spin 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 weir (a short or low dam) 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 and is released from the upper reservoir to power hydro turbines located below the upper reservoir. The electricity for pumping may be from hydroturbines or from other types of power plants including fossil fuel or nuclear power plants. They usually pump water to storage when electricity demand (or use) and prices are low and release the stored water to generate electricity when electricity demand and prices are higher. Pumped-storage hydroelectric systems generally use more electricity to pump water to the upper water storage reservoirs than they produce with the stored water.

History of hydropower

Hydropower is one of the oldest sources of energy for producing mechanical and electrical energy. Hydropower was used thousands of years ago to turn paddle wheels to help 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, when 16 brush-arc lamps were powered using a water turbine at the Wolverine Chair Factory in Grand Rapids, Michigan. The first U.S. hydroelectric power plant opened on the Fox River near Appleton, Wisconsin, on September 30, 1882. Most U.S. hydroelectricity is now produced at large dams on major rivers, and most of these hydroelectric dams were built before the mid-1970s.

Most U.S. hydroelectricity generation capacity is in the West

There are hydropower facilities in nearly every state. Most hydroelectricity is produced at large dams built by the federal government, and many of the largest hydropower dams are in the western United States.

About half of U.S. hydroelectricity generation capacity ² is in Washington, California, and Oregon. Washington has the most hydroelectric generating capacity of any state and is the site of the Grand Coulee Dam, the largest hydropower facility in the United States. New York has the largest hydroelectricity generation capacity of all states east of the Mississippi River, followed by Alabama.

In 2022, total U.S. conventional hydroelectricity net summer electricity generation capacity 79,980 megawatts (MW)-or about 80 million kilowatts.

Hydroelectricity generation varies with precipitation levels

Because hydroelectricity generation depends on precipitation, and precipitation levels vary seasonally and annually, the ranking of each state in annual hydroelectricity generation may be different from its ranking in generation capacity.

In 2022, total U.S. conventional hydroelectricity generation was equal to about 6.2% (about 262 billion kilowatthours [kWh]) of total U.S. utility-scale electricity generation

Most dams were not built for electricity generation

Only a small percentage of the dams in the United States produce electricity. Most dams were constructed for irrigation and flood control and do not have hydroelectricity generators. The U.S. Department of Energy estimated that in 2012, non-powered dams in the United States had a total of 12,000 megawatts (MW) of potential hydropower capacity.

Hydropower generators produce clean electricity, but hydropower does affect the environment

Most dams in the United States were built mainly for flood control, municipal water supply, and irrigation water. Although many of these dams have hydroelectric generators, only a small number of dams were built specifically for hydropower generation. Hydropower generators do not directly emit air pollutants. However, dams, reservoirs, and the operation of hydroelectric generators can affect the environment.

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A dam that creates a reservoir (or a dam that diverts water to a run-of-river hydropower plant) may obstruct fish migration. A dam and reservoir can also change natural water temperatures, water chemistry, river flow characteristics, and silt loads. All of these changes can affect the ecology and the physical characteristics of the river. These changes may have negative effects on native plants and on animals in and around the river. Reservoirs may cover important natural areas, agricultural land, or archeological sites. A reservoir and the operation of the dam may also result in the relocation of people. The physical impacts of a dam and reservoir, the operation of the dam, and the use of the water can change the environment over a much larger area than the area a reservoir covers.

Manufacturing the concrete and steel in hydropower dams requires equipment that may produce emissions. If fossil fuels are the energy sources for making these materials, then the emissions from the equipment could be associated with the electricity that hydropower facilities generate. However, given the long operating lifetime of a hydropower plant (50 years to 100 years) these emissions are offset by the emissions-free hydroelectricity.

Greenhouse gases (GHG) such as carbon dioxide and methane form in natural aquatic systems and in human-made water storage reservoirs as a result of the aerobic and anaerobic decomposition of biomass in the water. The exact amounts of GHG that form in and are emitted from hydropower reservoirs is uncertain and depend on many site specific and regional factors.

Fish ladders help salmon reach their spawning grounds

Hydropower turbines kill and injure some of the fish that pass through the turbine. The U.S. Department of Energy has sponsored the research and development of hydroturbines that could reduce fish deaths to lower than 2%, in comparison with fish kills of 5% to 10% for the best existing turbines.

Many species of fish, such as salmon and shad, swim up rivers and streams from the sea to reproduce in their spawning grounds in the beds of rivers and streams. Dams can block their way. Different approaches to fixing this problem include the construction of fish ladders and elevators that help fish move around or over dams to the spawning grounds upstream.

The gravitational pull of the moon and sun along with the rotation of the earth cause the tides. In some places, tides cause water levels near the shore to vary up to 40 feet. People in Europe harnessed this movement of water to operate grain mills more than a 1,000 years ago. Today, tidal energy systems generate electricity. Producing tidal energy economically requires a tidal range of at least 10 feet.

Tidal barrages

One type of tidal energy system uses a structure similar to a dam called a barrage. The barrage is installed across an inlet of an ocean bay or lagoon that forms a tidal basin. Sluice gates on the barrage control water levels and flow rates to allow the tidal basin to fill on the incoming high tides and to empty through an electricity turbine system on the outgoing ebb tide. A two-way tidal power system generates electricity from both the incoming and outgoing tides.

A potential disadvantage of tidal power is the effect a tidal station can have on plants and animals in estuaries of the tidal basin. Tidal barrages can change the tidal level in the basin and increase turbidity (the amount of matter in suspension in the water). They can also affect navigation and recreation.

Several tidal power barrages operate around the world. The Sihwa Lake Tidal Power Station in South Korea has the largest electricity generation capacity at 254 megawatts (MW). The oldest and second-largest operating tidal power plant is in La Rance, France, with 240 MW of electricity generation capacity. The next largest tidal power plant is in Annapolis Royal in Nova Scotia, Canada, with 20 MW of electricity generation capacity. China, Russia, and South Korea all have smaller tidal power plants.

The United States does not have any tidal power plants, and it only has a few sites where tidal energy could be economical to produce. France, England, Canada, and Russia have much more potential to use tidal power.

Tidal turbines

Tidal turbines look similar to wind turbines. They can be placed on the sea floor where there is strong tidal flow. Because water is about 800 times denser than air, tidal turbines have to be much sturdier and heavier than wind turbines. Tidal turbines are more expensive to build than wind turbines but capture more energy with the same size blades. A demonstration tidal turbine project is under development in the East River of New York.

Tidal fences

A tidal fence is a type of tidal power system that has vertical axis turbines mounted in a fence or row placed on the sea bed, similar to tidal turbines. Water passing through the turbines generates electricity. As of the end of 2021, no tidal fence projects were operating.

Waves have a lot of energy

CETO underwater wave energy device

Waves form as wind blows over the surface of open water in oceans and lakes. Ocean waves contain tremendous energy. The theoretical annual energy potential of waves off the coasts of the United States is estimated to be as much as 2.64 trillion kilowatthours, which is equal to about 64% of total U.S. utility-scale electricity generation in 2021. ( Utility-scale generation is from electric generators/power plants with at least one megawatt of generation capacity.) The west coasts of the United States and Europe, and the coasts of Japan and New Zealand, have potential sites for harnessing wave energy. Many different methods and technologies for capturing and converting wave energy to electricity are under development. These methods include placing devices on or just below the surface of the water and anchoring devices to the ocean floor.

Different ways to channel the power of waves

One way to harness wave energy is to bend or focus waves into a narrow channel to increase their size and power and to spin the turbines that generate electricity. Waves can also be channeled into a catch basin or reservoir where the water flows to a turbine at a lower elevation, similar to the way a hydropower dam operates.

The U.S. Department of Energy's Marine and Hydrokinetic Technology Database provides information on marine and hydrokinetic renewable energy, in the United States and around the world.

Ocean thermal energy conversion produces energy from temperature differences in ocean waters

Ocean thermal energy conversion (OTEC) is a process or technology for producing energy by harnessing the temperature differences (thermal gradients) between ocean surface waters and deep ocean waters.

Energy from the sun heats the surface water of the ocean. In tropical regions, surface water can be much warmer than deep water. This temperature difference can be used to produce electricity and to desalinate ocean water. Ocean Thermal Energy Conversion (OTEC) systems use a temperature difference (of at least 36° Fahrenheit or 20° Celsius) to power a turbine to produce electricity. Warm surface water is pumped through an evaporator containing a working fluid. The vaporized fluid drives a turbine/generator. The vaporized fluid is turned back to a liquid in a condenser cooled with cold ocean water pumped from deeper in the ocean. OTEC systems using seawater as the working fluid can use the condensed water to produce desalinated water.

The United States became involved in OTEC research in 1974 with the establishment of the Natural Energy Laboratory of Hawaii Authority. The laboratory is one of the world's leading test facilities for OTEC technology. The laboratory operated a 250 kilowatt (kW) demonstration OTEC plant for six years in the 1990s. The United States Navy supported the development of a 105 kW demonstration OTEC plant at the laboratory site. This facility became operational in 2015 and supplies electricity to the local electricity grid.

Other larger OTEC systems are in development or planned in several countries, mostly to supply electricity and desalinated water for island communities.

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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 is usually the largest single renewable energy source of annual electricity generation in the United States.

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What is geothermal energy?

Geothermal energy is heat within the earth. The word geothermal comes from the Greek words geo (earth) and therme (heat). Geothermal energy is a renewable energy source because heat is continuously produced inside the earth. People use geothermal heat for bathing, to heat buildings, and to generate electricity.

Geothermal energy comes from deep inside the earth

The slow decay of radioactive particles in the earth's core, a process that happens in all rocks, produces geothermal energy.

The earth has four major parts or layers:

An inner core of solid iron that is about 1,500 miles in diameter

An outer core of hot molten rock called magma that is about 1,500 miles thick.

A mantle of magma and rock surrounding the outer core that is about 1,800 miles thick

A crust of solid rock that forms the continents and ocean floors that is 15 to 35 miles thick under the continents and 3 to 5 miles thick under the oceans

Scientists have discovered that the temperature of the earth's inner core is about 10,800 degrees Fahrenheit (°F), which is as hot as the surface of the sun. Temperatures in the mantle range from about 392°F at the upper boundary with the earth's crust to approximately 7,230°F at the mantle-core boundary.

The earth's crust is broken into pieces called tectonic plates. Magma comes close to the earth's surface near the edges of these plates, which is where many volcanoes occur. The lava that erupts from volcanoes is partly magma. Rocks and water absorb heat from magma deep underground. The rocks and water found deeper underground have the highest temperatures.

Volcanoes and fumaroles (holes in the earth where volcanic gases are released)

Hot springs

Geysers

Most geothermal resources are near the boundaries of the earth's tectonic plates

The most active geothermal resources are usually found along major tectonic plate boundaries where most volcanoes are located. One of the most active geothermal areas in the world is called the Ring of Fire, which encircles the Pacific Ocean.

When magma comes near the earth's surface, it heats ground water trapped in porous rock or water running along fractured rock surfaces and faults. Hydrothermal features have two common ingredients: water (hydro) and heat (thermal).

Geologists use various methods to find geothermal reservoirs. Drilling a well and testing the temperature deep underground is the most reliable method for locating a geothermal reservoir.

U.S. geothermal power plants are located in the West

Most of the geothermal power plants in the United States are in western states and Hawaii, where geothermal energy resources are close to the earth's surface. California generates the most electricity from geothermal energy. The Geysers dry steam reservoir in Northern California is the largest known dry steam field in the world and has been producing electricity since 1960.

Direct use and district heating systems

Electricity generation power plants

Geothermal heat pumps

Direct use and district heating systems

Direct use and district heating systems use hot water from springs or reservoirs located near the surface of the earth. Ancient Roman, Chinese, and Native American cultures used hot mineral springs for bathing, cooking, and heating. Today, many hot springs are still used for bathing, and many people believe the hot, mineral-rich waters have natural healing powers.

Geothermal energy is also used to heat buildings through district heating systems. Hot water near the earth's surface is piped directly into buildings for heat. A district heating system provides heat for most of the buildings in Reykjavik, Iceland.

Industrial applications of geothermal energy include food dehydration, gold mining, and milk pasteurizing. Dehydration, or the drying of vegetable and fruit products, is the most common industrial use of geothermal energy.

Geothermal electricity generation

Geothermal electricity generation requires water or steam at high temperatures (300° to 700°F). Geothermal power plants are generally built where geothermal reservoirs are located, within a mile or two of the earth's surface.

The United States leads the world in the amount of electricity generated with geothermal energy. In 2021, there were geothermal power plants in seven states, which produced about 16 billion kilowatthours (kWh), equal to 0.4% of total U.S. utility-scale electricity generation.

State share of total U.S. geothermal electricity generation

Geothermal share of total state electricity generation

In 2021, 27 countries, including the United States, generated a total of about 92 billion kWh of electricity from geothermal energy. Indonesia was the second-largest geothermal electricity producer after the United States-nearly 16 billion kWh of electricity-and equal to 5% of Indonesia's total electricity generation. Kenya was the eighth-highest geothermal electricity producer at about 5 billion kWh. This was equal to about 43% of Kenya's annual electricity generation, which was the largest percentage share among all countries with geothermal power plants.

Geothermal heat pumps

Geothermal heat pumps use the constant temperatures near the surface of the earth to heat and cool buildings. Geothermal heat pumps transfer heat from the ground (or water) into buildings during the winter and reverse the process in the summer.

Geothermal power plants use hydrothermal resources that have both water (hydro) and heat (thermal). Geothermal power plants require high-temperature (300°F to 700°F) hydrothermal resources that come from either dry steam wells or from hot water wells. People use these resources by drilling wells into the earth and then piping steam or hot water to the surface. The hot water or steam powers a turbine that generates electricity. Some geothermal wells are as much as two miles deep.

Types of geothermal power plants

Dry steam plants use steam directly from a geothermal reservoir to turn generator turbines. The first geothermal power plant was built in 1904 in Tuscany, Italy, where natural steam erupted from the earth.

Flash steam plants take high-pressure hot water from deep inside the earth and convert it to steam to drive generator turbines. When the steam cools, it condenses to water and is injected back into the ground to be used again. Most geothermal power plants are flash steam plants.

Binary cycle power plants transfer the heat from geothermal hot water to another liquid. The heat causes the second liquid to turn to steam, which is used to drive a generator turbine.

Geothermal heat pumps use the earth's constant temperatures for heating and cooling

Although air temperatures above ground change throughout the day and with the seasons, temperatures of the earth 10 feet below ground are consistently between 50°F and 60°F. For most areas of the United States, this means soil temperatures are usually warmer than the air in winter and cooler than the air in summer. Geothermal heat pumps use the earth's constant temperature to heat and cool buildings. Geothermal heat pumps transfer heat from the ground (or water) into buildings during the winter and reverse the process in the summer.

Geothermal heat pumps are energy efficient and cost effective

According to the U.S. Environmental Protection Agency (EPA), geothermal heat pumps are the most energy-efficient, environmentally clean, and cost-effective systems for heating and cooling buildings. All types of buildings, including homes, office buildings, schools, and hospitals, can use geothermal heat pumps.

The environmental effects of geothermal energy depend on how geothermal energy is used or how it is converted to useful energy. Direct use applications and geothermal heat pumps may have a very small effect on the environment. In fact, they may reduce the use of energy sources that may have larger effects on the environment.

Geothermal power plants have low emission levels

Geothermal power plants do not burn fuel to generate electricity, but they may release small amounts of sulfur dioxide and carbon dioxide. Geothermal power plants emit 97% less acid rain-causing sulfur compounds and about 99% less carbon dioxide than fossil fuel power plants of similar size. Geothermal power plants use scrubbers to remove the hydrogen sulfide naturally found in geothermal reservoirs. Most geothermal power plants inject the geothermal steam and water that they use back into the earth. This water recycling can help to maintain the geothermal energy resource.

Many geothermal features are national treasures

Geothermal features in national parks, such as geysers and fumaroles in Yellowstone National Park, are protected by law.

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Geothermal energy is heat within the earth. The word geothermal comes from the Greek words geo (earth) and therme (heat). Geothermal energy is a renewable energy source because heat is continuously produced inside the earth. People use geothermal heat for bathing, to heat buildings, and to generate electricity.

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In 2020, of the energy generated in the United States was from large-scale hydropower plants. Hydroelectricity, which is created by hydropower plants, is a popular form of renewable energy that uses the flow of water to generate electricity.

Hydroelectricity is a renewable form of energy , but what are the other advantages this technology offers? Are there any disadvantages? The answer to both those questions is yes, let's find out why.

Pros and cons of hydroelectric energy

Hydropower has been used for generations to provide the U.S. with reliable, fossil fuel-free electricity.

It is a great renewable energy source because water is usually very abundant, but it comes with some environmental drawbacks. While the power source itself is carbon dioxide-free, building dams along a river can have consequences for the native fish species.

Generally, the pros outweigh the cons for hydropower because unlike solar or wind, water can be relied on 24/7.

How hydroelectric energy works

Hydropower plants create energy by using the force of water to turn turbines. They operate similarly to how a coal-powered plant is run.

For example, when coal is burned in a coal plant, the steam that is created powers turbines that then create electricity. With hydropower, the energy source that generates power is water.

The most popular form of hydropower, also known as hydroelectric power, is a large dam that holds water in a reservoir, like the picture below. When electricity is needed, water is released from the reservoir, which then propels turbines to produce electricity.
Hydropower plants are powered by water, which spins turbines to generate electricity. Image source: USGS
While hydroelectric dams are a great way to produce electricity, there are some disadvantages to them, which we will detail below.

Advantages of hydroelectric energy

1. Renewable

Hydroelectric energy is classified as a renewable energy source because it is powered by water, and water is a naturally replenishing resource.

Since water is the energy source that powers a hydropower plant, there is no pollution emitted during the generation of power. Both of these factors make hydropower renewable, because water is naturally replenishing and because it is not a source of greenhouse gas emissions.

Read more: Examples of renewable resources

2. Low emissions

The action of generating electricity with hydropower energy does not emit carbon dioxide, a greenhouse gas that drives global climate change.

After a hydropower plant is built, it does not emit pollution into the atmosphere like many of its non-renewable energy counterparts, like coal and natural gas.

3. Reliable

Hydroelectricity is a very reliable renewable energy source.

Water flow is usually very predictable and is taken into consideration when determining where a hydropower plant is built, either on an actively flowing river or built with a dam to manage water flow.

Additionally, the output of electricity can be adjusted. If energy demand is low, water can be averted from the turbines and less energy will be produced. The opposite is true if more energy is needed - more water can flow into the plant for electricity production.

4. Safe

Generally, hydropower is a very safe form of power generation.

No sickness-causing pollution is emitted during energy generation and there is zero chance of oil spills or gas pipes breaking, since the only fuel used to power a hydropower plant is water.

Disadvantages of hydroelectric energy

1. Environmental consequences

Hydropower facilities can be tricky because when one is built with a dam, such as the famous Hoover Dam in Nevada, a previously dry land area will be flooded with water, in order to be used as a reservoir. That means whatever habitat was in that location will be ruined. Also, the natural flow of the river will be affected.

A non-natural water flow leads to issues ranging from less sediment reaching the end of the river, a natural way to build up and maintain land, to affecting fish migration patterns. Also, many rivers travel through multiple counties and if they are dammed, upstream countries could take more water than is fair and leave less water for countries downriver.

Before choosing locations for hydropower plants, the potential environmental effects should be carefully considered to make sure that the plant can be as environmentally-friendly as possible.

2. Expensive to build

Building any type of power plant is expensive - hydroelectric power plants can cost as much as $580 per kilowatt to be built, and they usually range from 10MW to 30MWs (where one MW is equal to 1,000 kilowatts).

This means that the upfront cost of building a hydropower plant can be millions of dollars. Compared to the falling prices of solar installations, for example, hydropower is a more challenging renewable project to finance.

3. Drought potential

The ability to create electricity can be severely reduced if there is a drought and not enough water is flowing into the plant.

The good news is, most droughts are a short-lived break from the typical water cycle and should only create a minor delay in electricity generation.

4. Limited reservoirs

It is challenging to find a suitable spot that has a large year-round water supply, with the right amount of water and is close enough to existing power lines. It is also a delicate balancing act to keeping enough river water wild (meaning without dams), versus damming up many rivers for power.

Hydropower vs other renewable power sources

The main advantages of hydroelectric power are that it is 100% renewable, it can generate electricity at any time day or night, and its operation is generally safe.

However, it is challenging to build hydropower plants because you need to completely dam up a river. Not many utility companies can afford this, and usually governments foot the bill for hydropower plants.

Interestingly, states with a lot of hydropower plants tend to have cheaper electricity costs. So if states are willing to pay the upfront costs to build hydropower plants, they can reduce consumers' electric bills.

Solar power is a cheap source of renewable energy but hydroelectric power is more consistent since water is rushing through the turbines 24/7, versus the sun that only shines during the day.

While windpower is also a very consistent form of renewable power, wind turbines will have a higher maintenance cost than hydropower plants because the turbines are larger and constantly moving, meaning they break down more easily.

As for biofuels, hydropower is superior because once the plant is built and running, the environmental impacts are less. With biofuels, you need to constantly cut down trees or plants that will be burned for fuel. But with hydropower, water is plentiful and does not emit CO2 when powering the plant.

Learn more about the pros and cons of other renewable energy sources:

While no power source is perfect, hydropower can provide a good balance of renewable energy that produces reliable power with limited environmental impacts. To combat climate change, hydropower will be a necessary part of the U.S. energy mix because it is both greenhouse gas emissions free and a relatively simple and reliable way to produce clean energy.
Looking for lists of pros and cons for other types of energy sources?

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In 2020, of the energy generated in the United States was from large-scale hydropower plants. Hydroelectricity, which is created by hydropower plants, is a popular form of renewable energy that uses the flow of water to generate electricity. Hydroelectricity is a renewable form of energy , but what are the other advantages this technology offers?

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Green Mountain Energy: How does Geothermal Work

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Green Mountain Energy: How does Geothermal Work

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Renewable Energy 101: How Does Geothermal Energy Work?

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Kids learn about geothermal energy and how this renewable power can help the environment. Teach students about heat pumps and electric plants.

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Geothermal Energy: Harnessing the Power of the Earth | PBS LearningMedia

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Geothermal energy is a renewable energy source produced from the heat inside Earth. In this video from KQED, discover how it is produced and its limitations.

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Here are five important advantages of geothermal energy:

Reliable source of power

Small land footprint

Usable for large and small-scale installations

The geothermal energy industry is expanding

Geothermal infrastructure has longevity

Geothermal energy is a very reliable source of power

One of the most significant advantages of geothermal energy is that geothermal power is a very predictable and reliable source of energy, especially in comparison to other renewable energy resources like wind energy and solar energy. While wind and solar are more intermittent sources that require energy storage in order to be used most effectively at a large scale, geothermal power plants have a generally consistent power output no matter the time of day or season. This has many positive implications, notably that geothermal power is an appropriate source for meeting baseload energy demand.

Geothermal power plants have a small land footprint

Another advantage of geothermal power plants over other large-scale wind power, solar energy, or hydroelectric installations is the relatively low footprint of a geothermal plant. This is because, unlike wind, solar, and hydropower, geothermal energy comes from within the earth, and we don't need to build out collection setups over large swaths of land surface to harness it. For reference, National Geographic estimates that a geothermal power plant capable of producing one gigawatt-hour (GWh) of electricity would take up approximately 404 square miles of land surface, while a wind farm at the same energy output would need about 1,335 square miles, and a solar farm would need about 2,340 square miles. That's 88 percent less space for a geothermal power plant compared to a solar farm, both sized at one GWh.

There are large-scale and small-scale applications for geothermal power

Geothermal energy isn't just for large power plants; in fact, one of the most efficient ways to use heat from the earth is to harness it with a geothermal heat pump for a residential or commercial building. Unlike geothermal power plants, geothermal heat pumps take advantage of low-temperature geothermal reservoirs, which are available just about everywhere.

The geothermal energy industry is expanding quickly

The geothermal energy industry is relatively young, expanding with new technologies, research and development, and an influx of new projects. These enhancements to the industry are making geothermal energy more accessible, efficient, and applicable to a wider variety of use cases.

For example, a recent advancement in the geothermal energy extracting process, Enhanced Geothermal Systems (EGS), has made it possible to access deeper hydrothermal reservoirs. Hydrothermal reservoirs are where geothermal energy naturally occurs under the earth's surface, and the deeper the reservoir, the less heat and steam actually make it to the surface. EGSs create more open flow channels for steam to rise by fracturing rock with high-speed water. Ultimately, this makes extracting geothermal energy from deeper reservoirs more feasible.

Geothermal energy infrastructure has longevity

Geothermal heating and cooling systems have a very long lifespan in comparison to many other green energy solutions. The US Department of Energy estimates a 20-year lifespan for heat pumps and up to 50 years for the underground infrastructure.

Disadvantages of geothermal energy

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The Top Pros And Cons of Geothermal Energy

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Weigh the pros and cons of geothermal energy on EnergySage. Equip yourself with knowledge and choose wisely. Discover more today!