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The National Academies presents: What You Need to Know About Energy

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Want to understand the basics of America's current energy situation? The National Academies, advisers to the nation on science, engineering, and medicine, provides objective information about the United States' current energy sources and uses, as well as a look forward to the future of energy.

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Biomass or Bioenergy refers to the use of organic material to produce energy.

Biomass
Definition
Biomass refers to the organic material that is used for production of energy. This energy production process is referred to as Bioenergy. Biomass is primarily found in the form of living or recently living plants and biological wastes from industrial and home use. Due to the breadth of the term, the physical composition of biomass is inconsistent, but generally includes carbon, water and organic volatiles.

For the production of energy from biomass, the term feedstock is used to refer to whatever type of organic material will be used to produce a form of energy. The feedstock must then be converted to a usable energy form through one of many processes.

Feedstock + Process -> Usable Energy Form

Some common biomass conversion processes include:

Combustion: the process by which flammable materials are burned in the presence of air or oxygen to release heat. It is the simplest method by which biomass can be used for energy. In its rudimentary form, combustion is used for space heating (i.e. a fire for warmth) but can also be used to heat steam for electricity generationBiomass Energy Centre.(BEC). Combustion. February 2015 http://www.biomassenergycentre.org.uk/portal/page?_pageid=75,17502&_dad=portal&_schema=PORTAL Biomass Energy Centre.(BEC). Combustion. February 2015 http://www.biomassenergycentre.org.uk/portal/page?_pageid=75,17502&_dad=portal&_schema=PORTAL Biomass Energy Centre.(BEC). Combustion. February 2015 http://www.biomassenergycentre.org.uk/portal/page?_pageid=75,17502&_dad=portal&_schema=PORTAL .

Gasification: is the conversion of biomass into a combustible gas mixture referred to as Producer Gas (CO+H²+CH⁴) or Syngas. The gasification process uses heat, pressure and partial combustion to create syngas, which can then be used in place of natural gas Aboriginal Ankur Corporation (AAC). What is Biomass Gasification? February 2015 http://aboriginalankur.com/category/what-is-biomass-gasification/ Aboriginal Ankur Corporation (AAC). What is Biomass Gasification? February 2015 http://aboriginalankur.com/category/what-is-biomass-gasification/ Aboriginal Ankur Corporation (AAC). What is Biomass Gasification? February 2015 http://aboriginalankur.com/category/what-is-biomass-gasification/ .

Pyrolysis: Consists of thermal decomposition in the absence of oxygen. It is the precursor to gasification, and takes place as part of both gasification and combustionBiomass Energy Centre.(BEC). Pyrolysis. February 2015http://www.biomassenergycentre.org.uk/portal/page?_pageid=75,17506&_dad=portal&_schema=PORTAL Biomass Energy Centre.(BEC). Pyrolysis. February 2015http://www.biomassenergycentre.org.uk/portal/page?_pageid=75,17506&_dad=portal&_schema=PORTAL . The products of pyrolysis include gas, liquid and a sold char, with the proportions of each depending upon the parameters of the process.

Anaerobic digestion (or biodigestion): is the process whereby bacteria break down organic material in the absence of air, yielding a biogas containing methane and a solid residue. The methane can then be captured to produce energy. Similarily, the solid residue can also be burned to produce energy.

Fermentation: involves the conversion of a plant's glucose (or carbohydrate) into an alcohol or acid. Yeast or bacteria are added to the biomass material, which feed on the sugars to produce ethanol (an alcohol) and carbon dioxide. The ethanol is distilled and dehydrated to obtain a higher concentration of alcohol to achieve the required purity for the use as automotive fuel. The solid residue from the fermentation process can be used as cattle-feed and in the case of sugar cane can be used as a fuel for boilers or for subsequent gasification.

Some feedstocks are more conducive for certain biomass conversion processes than others. The determination of which feedstocks and processes will be used is determined largely by the availability of resources and the desired end form of energy.
Context
Prior to the industrial revolution, biomass was the primary source of energy. Biomass now makes up only a small percentage of total world energy use. However, for approximately 2.5 billion people, it remains the primary source of energy for cooking and heating. The use of biomass is highly contextual to the region in which it is used - availability of resources, availability of technology and economic viability are all drivers of biomass use.

Some jurisdictions - especially those with sustainable forestry initiatives - have declared biomass a "carbon neutral" energy source. This is based upon the logic that carbon emissions from burning biomass will be recaptured by the plants grown to feed biomass reactors in the future, thus forming a carbon cycle for the plant Vieira da Rosa, A. (2013). Fundamentals of Renewable Energy Processes (3rd ed.). Oxford, UK: Academic Press. Vieira da Rosa, A. (2013). Fundamentals of Renewable Energy Processes (3rd ed.). Oxford, UK: Academic Press. .

The environmental benefits and costs are highly contextual depending on the technology and feedstocks used. While some biomass processes such as waste-to-energy are touted for their lower CO2 emissions, some processes, such as combustion, release carbon dioxide and particulate matter that is a significant concern for human health.

The world's most energy-poor peoples and regions still rely on biomass for the majority of their energy needs Bridge, G., & le Billon, P. (2013) Oil. Cambridge, UK: Polity Press. . The lack of appropriate ventilation mechanisms for burning biomass is a major health concern and contributes to short life expectancies in much of the developing world.

Concerns associated with biomass go beyond human health. Depending upon the source of biomass used, deforestation, cropland degradation (due to diverting agricultural residues), and land use alteration can all be relevant issues associated with biomass.

References

1. ^ Biomass Energy Centre.(BEC). Combustion. February 2015 http://www.biomassenergycentre.org.uk/portal/page?_pageid=75,17502&_dad=portal&_schema=PORTAL

2. ^ Aboriginal Ankur Corporation (AAC). What is Biomass Gasification? February 2015 http://aboriginalankur.com/category/what-is-biomass-gasification/

3. ^ Biomass Energy Centre.(BEC). Pyrolysis. February 2015http://www.biomassenergycentre.org.uk/portal/page?_pageid=75,17506&_dad=portal&_schema=PORTAL

4. a, b Bridge, G., & le Billon, P. (2013) Oil. Cambridge, UK: Polity Press.

5. ^ Vieira da Rosa, A. (2013). Fundamentals of Renewable Energy Processes (3rd ed.). Oxford, UK: Academic Press.

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Biomass or Bioenergy refers to the use of organic material to produce energy. Definition Biomass refers to the organic material that is used for production of energy. This energy production process is referred to as Bioenergy. Biomass is primarily found in the form of living or recently living plants and biological wastes from industrial and home use.

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Is Biomass Really Renewable?
Updated October 19, 2016
Biomass, a renewable energy source derived from organic matter such as wood, crop waste, or garbage, makes up 4.8 percent of total U.S. energy consumption and about 12 percent of all U.S. renewable energy. Wood is the largest biomass energy source. In the U.S., there are currently 227 biomass plants operating. In the U.K., 35 are operating, 15 are under construction and 17 have been proposed. But just how renewable is biomass energy?

There are several ways to produce energy from biomass, including burning biomass to generate heat or run steam turbines that produce electricity, burning biomass to produce heat in thermal systems (when combined with electricity generation, it's called "combined heat and power"), turning feedstocks into liquid biofuels, and harvesting gas from landfills or anaerobic digesters. Biomass can consist of wood from forests and logging residues, sawdust from lumbermills, construction or organic municipal waste, energy crops (switchgrass), crop residue, and even chicken litter. Since the rapid expansion of biomass energy today relies largely on wood from forests, we'll focus here on energy produced by the combustion of biomass from forest wood and woody residue.

According to the U.S. Forest Service, "Wood is an abundant, sustainable, homegrown cellulosic resource that can significantly contribute to meeting 30 percent of U.S. petroleum consumption from biomass sources by 2030 and help create a more stable energy future, improve environmental quality, and increase economic opportunities."

Biomass advocates maintain that thinning out small-diameter or dead trees from overcrowded forests, and harvesting the byproducts of forest management such as limbs, treetops, needles, leaves, etc. improves the health of the trees that remain in the forest and helps reduce the incidence of wildfires. Biomass creates jobs and supports local economies by providing new markets for farmers and forest owners. It can also lessen our dependence on fossil fuels, and under certain conditions, can reduce greenhouse gas emissions.

Biomass is considered a renewable energy source because its inherent energy comes from the sun and because it can regrow in a relatively short time. Trees take in carbon dioxide from the atmosphere and convert it into biomass and when they die, it is released back into the atmosphere. Whether trees are burned or whether they decompose naturally, they release the same amount of carbon dioxide into the atmosphere. The idea is that if trees harvested as biomass are replanted as fast as the wood is burned, new trees take up the carbon produced by the combustion, the carbon cycle theoretically remains in balance, and no extra carbon is added to the atmospheric balance sheet-so biomass is arguably considered "carbon neutral." Since nothing offsets the CO2 that fossil fuel burning produces, replacing fossil fuels with biomass theoretically results in reduced carbon emissions.

In fact, the reality is a lot more complicated. In 2014, the U.S. Environmental Protection Agency (EPA) found that "carbon neutrality cannot be assumed for all biomass energy a priori." Whether or not biomass is truly carbon neutral depends on the time frame being studied, what type of biomass is used, the combustion technology, which fossil fuel is being replaced (since the combustion of both fossil fuels and biomass produces carbon dioxide), and what forest management techniques are employed in the areas where the biomass is harvested.

In 2010, a group of prominent scientists wrote to Congress explaining that the notion that all biomass results in a 100 percent reduction of carbon emissions is wrong. Biomass can reduce carbon dioxide if fast growing crops are grown on otherwise unproductive land; in this case, the regrowth of the plants offsets the carbon produced by the combustion of the crops. But cutting or clearing forests for energy, either to burn trees or to plant energy crops, releases carbon into the atmosphere that would have been sequestered had the trees remained untouched, and the regrowing and thus recapture of carbon can take decades or even a century. Moreover, carbon is emitted in the combustion process, resulting in a net increase of CO2.

Nevertheless, biomass energy is currently considered renewable, and thus qualifies for tax credits, subsidies and incentives in the U.S. These include the Renewable Electricity Production Tax Credit which pays closed-loop (organic matter planted exclusively to produce electricity) biomass energy producers $.023 per kilowatt-hour and open-loop biomass (any other waste or residue) producers $.012 per kilowatt-hour; and Renewable Energy Certificates wherein every megawatt hour of electricity generated by biomass earns a credit that can be sold, traded or bartered, giving its owner the right to claim to have purchased renewable energy. The Investment Tax Credit will reimburse 30 percent of biomass plant development if construction is begun by the end of this year, and if operation begins by 2024. And biomass is eligible for subsidies from the U.S. Department of Agriculture.

In part due to these incentives and the pressure to reduce coal use, energy companies in the U.S. and Europe are turning to biomass. By 2030, biomass could account for 60 percent of total final global renewable energy use, according to the International Renewable Energy Agency.

Most of the new biomass electricity generating plants being proposed in the U.S. will burn wood. Plants in the Southeast U.S. are churning out wood pellets to meet Europe's increasing need for wood. Last year, wood pellet exports from the Southeast increased 70 percent; the Southern U.S. is now the largest exporter of wood pellets in the world. Since there isn't enough logging residue to meet the increased demand for biomass, many fear that more standing trees will be chopped and more forests clear-cut.

The new biomass plants produce 38 megawatts of electricity on average, but many are being built in the 50 to 110 megawatt range. According to the Partnership for Policy Integrity, a 50-megawatt plant burns 2,550 lb. of green wood each minute. As an example, the 50-megawatt McNeil plant in Burlington, VT burns 625,000 tons of green wood from trees and residue each year. Additional wood is needed for co-firing in coal plants where wood is burned with coal to meet state renewable energy mandates (resulting in additional carbon emissions), pellet production, and liquid biofuels. While admittedly most forests will not actually be clear-cut for biomass energy, the numbers make clear the amount of pressure that will be brought to bear on our forests.

How is this increase in biomass burning impacting climate change, our health, and the environment? Today's biomass-burning power plants actually produce more global warming CO2 than fossil fuel plants: 65 percent more CO2 per megawatt hour than modern coal plants and 285 percent more CO2 than natural gas combined cycle plants (which use both a gas and steam turbine together). In addition, burning wood biomass emits as much, if not more, air pollution than burning fossil fuels-particulate matter, nitrogen oxides, carbon monoxide, sulfur dioxide, lead, mercury, and other hazardous air pollutants-which can cause cancer or reproductive effects. The air pollution from biomass facilities, which the American Heart Association and the American Lung Association have called a danger to public health, produces respiratory illnesses, heart disease, cancer, and developmental delays in children.

Harvesting and removing limbs, leaves and plant parts from forests, which would normally recycle nutrients back into the soil as they decay, can diminish soil fertility and hasten erosion. Heavy machinery used for Iogging compacts soil and increases runoff, which may affect water quality. Removing vegetation from the ground also impacts wildlife habitats on the forest floor.

For five years, the EPA has been reassessing the climate impacts of biomass burning; it is still not clear how wood energy will eventually be regulated, but a decision is expected this year. The agency has been working with scientists to develop formulas so that states and power plant owners can calculate the climate impacts of wood fuel.

Members of the U.S. Senate recently proposed an amendment to the Energy Policy Modernization Act that would deem forest biomass "carbon neutral." Under President Obama's Clean Power Plan to reduce greenhouse gas emissions from power plants, this measure would make biomass equivalent to zero-emission wind and solar energy as a replacement for coal. In response, 65 scientists and stakeholders wrote a letter to the Senate protesting that "Granting carbon amnesty to forest biomass burning for energy could lead to significant depletion of U.S. forests. The potential implications of declaring carbon neutrality for forest biofuels are great because even small quantities of bioenergy require large quantities of wood. The U.S. Energy Information Agency estimates that for each 1 percent added to current U.S. electricity production from forest biomass an additional 18 percent increase in U.S. forest harvest is required. This policy would also encourage the destruction of forests in developing countries that would see the U.S. as an export market....We urge you and other members of the Senate to reconsider this well-intentioned legislation and eliminate the misrepresentation that forest bioenergy is carbon-neutral."

As the thinking about biomass continues to evolve, state, federal, and international regulations need to clearly distinguish between the types of biomass energy that are beneficial and those that are detrimental. Treating all biomass, regardless of its source, as carbon neutral, could lead to increased greenhouse gas emissions at home and around the world. As the scientists said in their 2010 letter to Congress, the "globally improper accounting of bioenergy could lead to large-scale clearing of the world's forests... any legal measure to reduce greenhouse gas emissions must include a system to differentiate emissions from bioenergy based on the source of the biomass."

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Updated October 19, 2016 Biomass, a renewable energy source derived from organic matter such as wood, crop waste, or garbage, makes up 4.8 percent of total U.S. energy consumption and about 12 percent of all U.S. renewable energy. Wood is the largest biomass energy source. In the U.S., there are currently 227 biomass plants operating.

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Many energy resources use steam turbine technology. Here are the parts you need to know.

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A steam turbine generator works by heating water to extremely high temperatures until it is converted into steam, then the steam energy is used to rotate the blades of a turbine to create mechanical or rotational energy.

This rotational energy caused by the high pressured steam turbine is used to generate electricity from an attached generator.

This video fully explains the diagram below, or read the step-by-step tutorial on how a steam turbine works:

In the diagram below we see a simplified example of how a steam energy turbine works. Here is a simple step by step guide:

(1) A heat source of some sort - perhaps a combusted fossil fuel or solar heat - is used to create heat energy.

(2) The boiler, which contains water, uses the heat energy to convert the water into high pressure steam.

Moving on, from the diagram above you can see next step in the steam turbine process:

(3) If the system is using a combustible fossil fuel as a heat source, then an exhaust pipe is needed to release the pollutants. If the system uses solar energy for the heat conversion, then an exhaust pipe is not needed because the solar energy system will not release any pollutants.

(4) The steam from the water in the boiler is pumped into the steam turbine. The steam energy spins the turbine blades.

(5) The generator is attached to the steam turbine by a rotating shaft. As the steam turbine spins, the generator spins and creates electricity.

(6) The steam that uses it's energy to spin the turbine passes through and is cooled using a cooling tower. The steam could alternatively be cooled naturally, perhaps using a lake or river,

(7) The cooling tower releases the already used, lower energy, and cooled steam into the atmosphere. The remaining water that is cooled back into a liquid state is pumped back into the boiler and repeats the process again, creating more energy from steam.

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Steam Turbine - How Steam Energy Works | TurbineGenerator

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A steam turbine generator works by heating water to extremely high temperatures until it is converted into steam, then the steam energy is used to rotate the blades of a turbine to create mechanical or rotational energy. This rotational energy caused by the high pressured steam turbine is used to generate electricity from an attached generator.

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Explore pros and cons of each energy source, including cost of production, pollution output, and availability.

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Many different articles on the issues involved with nuclear energy

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Many different articles on the issues involved with nuclear energy

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The Union of Concerned Scientists puts rigorous, independent science to work to solve our planet's most pressing problems. Joining with citizens across the country, we combine technical analysis and effective advocacy to create innovative, practical solutions for a healthy, safe, and sustainable future.

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We Need Your Support
to Make Change Happen

We can shift our nation away from dirty fossil fuels and toward cleaner, renewable sources of power-but not without you. Your generous support helps develop science-based solutions for a healthy, safe, and sustainable future.

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Our Energy Choices: Coal and Other Fossil Fuels

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Fossil fuels-coal, natural gas, and oil-have powered America for more than a century, but their production and use have significant health and environmental impacts, including air and water pollution, environmental degradation, and global warming. Learn more about the technology and costs of fossil fuels.

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How Hydroelectric Power works AND environmental concerns

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How Hydroelectric Power works AND environmental concerns

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By taking advantage of gravity and the water cycle, we have tapped into one of nature's engines to create a useful form of energy. In fact, humans have been capturing the energy of moving water for thousands of years. Today, harnessing the power of moving water to generate electricity, known as hydroelectric power, is the largest source of emissions-free, renewable electricity in the United States and worldwide.

Although the generation of hydropower does not emit air pollution or greenhouse gas emissions, it can have negative environmental and social consequences. Blocking rivers with dams can degrade water quality, damage aquatic and riparian habitat, block migratory fish passage, and displace local communities. The benefits and drawbacks of any proposed hydropower development must be weighed before moving forward with any project. Still, if it's done right, hydropower can be a sustainable and nonpolluting source of electricity that can help decrease our dependence on fossil fuels and reduce the threat of global warming.

The hydropower resource

On Earth, water is constantly moved around in various states, a process known as the hydrologic cycle. Water evaporates from the oceans, forming into clouds, falling out as rain and snow, gathering into streams and rivers, and flowing back to the sea. All this movement provides an enormous opportunity to harness useful energy.

In 2011, hydropower provided 16 percent of the world's electricity, second only to fossil fuels. Worldwide capacity in 2011 was 950 gigawatts (GW), with 24 percent in the China, eight percent in the United States, and nine percent in Brazil [ 1]. Globally, hydroelectric capacity has more than doubled since 1970.

In the United States, hydropower has grown steadily, from 56 GW of installed capacity in 1970 to more than 78 GW in 2011 [ 2]. However, as a percentage of total U.S. electricity generation, it has fallen from 12 percent in 1980 to 7 percent in 2012, largely as a result of the rapid growth in natural gas power plants and other renewable energy technologies such as wind and solar [ 3].

Since hydropower depends on rivers and streams for generation, the potential to use hydropower as a source of electricity varies across the country. For example, the Pacific Northwest (Oregon and Washington) generates more than two-thirds of its electricity from hydroelectric dams [ 4]. The Grand Coulee dam on the Columbia River in Washington is one of the largest dams in the world, with a capacity of more than 6,750 megawatts (MW).

In addition to very large plants in the western states, the United States has many smaller hydropower plants. In 1940 there were 3,100 hydropower plants across the country, though by 1980 that number had fallen to 1,425. Since then, a number of these small plants have been restored; as of 2013, there were 1,672 hydro plants (not including pumped storage) in operation [ 5]. These plants account for only a tiny fraction of the dams that block and divert our rivers.

Converting moving water to electricity

In order to generate electricity from the kinetic energy in moving water, the water has to move with sufficient speed and volume to spin a propeller-like device called a turbine, which in turn rotates a generator to generate electricity. Roughly speaking, one gallon of water per second falling one hundred feet can generate one kilowatt of electricity.

To increase the volume of moving water, impoundments or dams are used to collect the water. An opening in the dam uses gravity to drop water down a pipe called a penstock. The moving water causes the turbine to spin, which causes magnets inside a generator to rotate and create electricity.

There are a variety of types of turbines used at hydropower facilities, and their use depends on the amount of hydraulic head (vertical distance between the dam and the turbine) at the plant. The most common are Kaplan, Francis, and Pelton wheel designs. Some of these designs, called reaction and impulse wheels, use not just the kinetic force of the moving water but also the water pressure.

The Kaplan turbine is similar to a boat propeller, with a runner (the turning part of a turbine) that has three to six blades, and can provide up to 400 MW of power. The Kaplan turbine is differentiated from other kinds of hydropower turbines because its performance can be improved by changing the pitch of the blades. The Francis turbine has a runner with nine or more fixed vanes. In this turbine design, which can be up to 800 MW in size, the runner blades direct the water so that it moves in an axial flow [ 6]. The Pelton turbine consists of a set of specially shaped buckets that are mounted on the outside of a circular disc, making it look similar to a water wheel. Pelton turbines are typically used in high hydraulic head sites and can be as large as 200 MW.

Hydropower can also be generated without a dam, through a process known as run-of-the-river. In this case, the volume and speed of water is not augmented by a dam. Instead, a run-of-river project spins the turbine blades by capturing the kinetic energy of the moving water in the river. Hydropower projects that have dams can control when electricity is generated because the dams can control the timing and flow of the water reaching the turbines. Therefore these projects can choose to generate power when it is most needed and most valuable to the grid. Because run-of-river projects do not store water behind dams, they have much less ability to control the amount and timing of when electricity is generated.

Another type of hydropower technology is called pumped storage. In a pumped storage plant, water is pumped from a lower reservoir to a higher reservoir during off-peak times when electricity is relatively cheap, using electricity generated from other types of energy sources. Pumping the water uphill creates the potential to generate hydropower later on. When the hydropower power is needed, it is released back into the lower reservoir through turbines. Inevitably, some power is lost, but pumped storage systems can be up to 80 percent efficient. There is currently more than 90 GW of pumped storage capacity worldwide, with about 20 percent of that in the United States. The need to create storage resources to capture and store for later use the generation from high penetrations of variable renewable energy (e.g. wind and solar) could increase interest in building new pumped storage projects [ 7].

Environmental and societal concerns

While hydropower generation does not emit global warming gasses or other air pollutants, the construction and operation of hydropower projects can have environmental and societal consequences that greatly depend on where the project is located and how it is operated.

Dams that have flooded areas with live vegetation can emit methane, a powerful global warming gas, as that organic material decomposes. For example, the Tucurui dam in Brazil created a reservoir in the rainforest before clearing the trees. As the plants and trees began to rot, they reduced the oxygen content of the water, killing off the plants and fish in the water, and released large quantities of methane.

Hydropower projects can reduce the flows in rivers downstream if the upstream flows are trapped behind a reservoir and/or diverted into canals that take the water off stream to a generation unit. Lowering the flows in a river can alter water temperatures and degrade habitat for plants and animals. Less water in the river can also reduce oxygen levels which damage water quality.

Water is typically stored behind a dam and released through the turbines when power is needed. This creates artificial flow patterns in the downstream river that may be very different from the flow patterns a river would naturally experience. For example, rivers fed mostly by snowmelt may experience much higher flows in the winter and spring than the summer and fall. Hydropower operations may differ from these natural flow patterns, which has implications for downstream riparian and aquatic species. If water levels downstream of a hydropower project fluctuate wildly because of generation operations, fish could be stranded in suddenly shallow waters. If operations cause a more static flow schedule throughout the year than what the river would normally experience, the movement of sediment along a river section could be disrupted, reducing habitat for aquatic species. Fewer seasonal flow events could also cause a riparian corridor to thicken into a less dynamic channel as saplings that would usually be seasonally thinned by high flows are able to mature.

Dams can also block the migration of fish that swim upstream to reach spawning grounds. In the Pacific Northwest and California, large dams have blocked the migration of coho, chinook, and sockeye salmon from the ocean to their upstream spawning grounds. The number of salmon making the journey upstream has fallen 90 percent since the construction of four dams on the lower Snake River. Some steps are being taken to move fish around the dams, such as putting them in barges or building fish ladders, but success has been limited. Downstream fish passage can also be a challenge since young fish can be chewed up in the turbines of the dam as they head towards the ocean.

The flooding of land to create reservoirs can also eliminate areas where people live or grow crops. The Balbina dam in Brazil, for example, flooded 2,360 square kilometers, an area the size of Delaware [ 8]. Population density is typically higher along rivers, leading to mass dislocation of urban centers. The Three Gorges Dam in China dislocated nearly 1.2 million people [ 9].

Wildlife habitats destroyed by reservoirs can be especially valuable. In South America, 80 percent of the hydroelectric potential is located in rain forests, one of the most rich and diverse ecosystems on Earth. The Rosana dam in Brazil destroyed one of the few remaining habitats of the black-lion tamarin, a rare and beautiful species of long-haired monkey.

In the United States, most non-federal hydropower plants are required to obtain an operating license from the Federal Energy Regulatory Commission (FERC). These licenses, which govern the operations of a plant for 30 to 50 years, play a large role in determining how a hydropower facility's operations impact local environmental, cultural, and recreational resources. Therefore, the re-licensing process is an important opportunity to reassess and adjust, if necessary, the operations of a project to better align itself with the current needs and values of the environment and the public. Hydropower re-licensing processes across the country have resulted in increased flows to support aquatic and riparian habitats, better access and services to support public recreation on rivers, and protection of cultural heritage sites [ 10].

Low impact hydropower

While hydropower operations can cause negative environmental impacts, the way a project is operated can make a big difference in its degree of environmental footprint. Projects can manage flow releases from dams to ensure there is enough water in the river to support native species. Flows can also be scheduled to mimic natural flow patterns, which help transport sediment and mimic biological cues that would have been provided by the natural flow cycle. Retrofitting dams with fish passage equipment and even removing dams in some key river reaches can greatly improve access to upstream habitat.

Hydroelectric facilities that want to reduce their environmental impacts can undergo a voluntary certification program developed by the Low Impact Hydropower Institute (LIHI). LIHI is a nationally recognized independent nonprofit organization dedicated to reducing the harmful impacts of hydropower generation by creating a credible and transparent standard for consumers to use in evaluating hydropower. Through the establishment of the Low Impact Hydropower Certification Program, LIHI certifies hydropower facilities with environmental and social impacts that are low compared with other hydropower facilities based on objective criteria.

To be LIHI-certified, a facility must adequately protect or mitigate its impacts in the following areas: river flows, water quality, fish passage and protection, watershed protection, threatened and endangered species protection, cultural resource protection, recreation, and facilities recommended for removal. The certification criteria are based on the more recent and most stringent mitigation measures recommended for the hydropower project by state and federal resource agencies, even if those measures are not a requirement for operating the facility [ 11].

The future of hydropower

Advances in 'fish-friendly' turbines and improved data collection techniques to increase the effectiveness of fish passage technologies create exciting new opportunities for the hydropower industry. If constructed and operated in a manner that minimizes environmental and cultural impacts, hydropower projects can provide low-cost, clean sources of electricity to urban and rural areas throughout the world. Harvesting the power from our rivers can be part of a smart and diverse set of solutions for reducing our dependence on fossil fuels, and the impact they have on our climate and public health. The ability to ramp up and down hydropower generation is a valuable source of flexible generation on the electricity grid, which can directly displace coal and natural gas, and help integrate larger amounts of variable renewable energy resources, like wind and solar power.

Since most developed countries have already developed their most accessible areas for large-scale hydropower, growth of these projects will likely be concentrated in nations with growing populations and developing economies. According to the International Hydropower Association, more than 30 GW of new hydropower capacity was commissioned in 2012, with significant investment occurring in South America, Asia, and Africa [ 12]. In Brazil, three large projects are under construction in the Amazon region totaling more than 22 GW of generation capacity.

The potential to develop new large-scale hydropower projects in the United States is generally low. However, the U.S. Department of Energy and the Oak Ridge National Laboratory released a hydropower mapping tool in 2014 that estimates more than 65 GW of potential new hydropower development across more than three million U.S. rivers and streams that currently do not have hydropower development [ 13]. The study identified western states, including Alaska, California, Colorado, Idaho, Montana, Oregon, and Washington as having the greatest new hydropower development potential. The study builds upon a DOE-funded study released in 2012 that estimated 12 GW of hydropower potential at the nation's 80,000 non-powered dams [ 14]. There is also additional potential to increase electricity generation at existing hydropower projects by expanding storage, upgrading equipment, and increasing efficiency.
References:
[1] International Energy Agency (IEA). 2012. Key World Energy Statistics. Paris, France. Online at: http://www.iea.org/publications/freepublications/publication/kwes.pdf

[2] Energy Information Administration (EIA). 2011. Electric Power Annual. Table 4.3. Existing Capacity by Energy Source, 2011 (Megawatts). Online at http://www.eia.gov/electricity/annual/html/epa_04_03.html

[3] Energy Information Administration (EIA). 2011. International Energy Statistics. Renewables: Electricity Generation: Hydroelectric. Online at: http://www.eia.gov/cfapps/ipdbproject/iedindex3.cfm?tid=6&pid=33&aid=12&cid=US,&syid=1980&eyid=2011&unit=BKWH

[4] Energy Information Administration (EIA). 2012. Electric Power Annual. Table 3.6 Net Generation from Hydroelectric (Conventional) Power. Online at: http://www.eia.gov/electricity/annual/html/epa_03_06.html

[5] SNL data.

[6] U.S. Department of Energy (DOE). Types of Hydropower Turbines. Online at http://www1.eere.energy.gov/water/hydro_turbine_types.html

[7] The Role of Pumped Storage Hydro Resources in Electricity Markets and System Operation. National Renewable Energy Laboratory. May 2013. Online at: http://www.nrel.gov/docs/fy13osti/58655.pdf

[8] Fearnside, Phillip M. 1989. Brazil's Balbina Dam: Environment versus the legacy of the Pharaohs in Amazonia. Environmental Management, July/Aug 1989, Volume 13, Issue 4, pp 401-423.

[9] International Rivers. Online at http://www.internationalrivers.org.

[10] Hydropower Reform Coalition. Online at http://www.hydroreform.org.

[11] Low Impact Hydropower Institute. Online at http://www.lowimpacthydro.org.

[12] International Hydropower Association. 2013 IHA Hydropower Report. Online at http://www.hydropower.org/report.

[13] U.S. Department of Energy (DOE). New Stream-reach Development Resource Assessment. Online at http://nhaap.ornl.gov/nsd.

[14] U.S. Department of Energy (DOE). An Assessment of Energy Potential at Non-Powered Dams in the United States. April 2012. Online at http://energy.gov/sites/prod/files/2013/12/f5/npd_report_0.pdf.

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By taking advantage of gravity and the water cycle, we have tapped into one of nature's engines to create a useful form of energy. In fact, humans have been capturing the energy of moving water for thousands of years.

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Natural Gas

Natural gas provides 29% of our energy and is used to heat about half the homes in the United States. It is also a raw material in a variety of common products, such as paints, fertilizers, plastics, medicines, and antifreeze. Propane, which powers many kitchen stoves and outdoor grills as well as home heating systems, is derived from natural gas. Natural gas is also used to generate 33% of our electricity.

Unlike oil, about one-fourth of which is imported at present, virtually all of our natural gas comes from the United States.

Natural gas is often described as "clean burning" because it produces fewer undesirable by-products per unit energy than coal or petroleum. Like all fossil fuels, its combustion emits carbon dioxide, but at about half the rate of coal per kilowatt hour of electricity generated. It is also more energy efficient. On average, a typical coal-burning power plant in 2013 was about 33% efficient in converting heat energy into electrical power. A gas-fired plant was about 42% efficient. And in natural gas combined-cycle power plants-in which waste heat from a natural gas turbine is used to power a steam turbine-generation may be as much as 60% efficient.

Unlike oil, about one-fourth of which is imported at present, virtually all of our natural gas comes from the United States. Annual consumption is projected to rise by about 25% during the next 25 years, from 28.3 trillion cubic feet (tcf) in 2015 to 35.4 tcf in 2040. But the pace of discovery may rise even faster: According to the U.S. Energy Information Administration (EIA), the U.S. total proved reserves of natural gas rose by 10% in 2014 alone and reached a record high for the United States of 389 tcf. Although the United States imports some of its natural gas, it also exports a growing amount, and net imports make up less than 4% of U.S. consumption.

One reason for that increase is expanded extraction by hydraulic fracturing ("fracking") of natural gas trapped in shale and other formations, a large resource that has increased nearly nine-fold since 2007. The EIA projects that within 25 years, shale gas will make up more than half of total domestic natural gas production. However, there are many unanswered questions about the long-term environmental impacts of the methods used to extract gas from shale.

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The National Academies presents: What You Need to Know About Energy

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Want to understand the basics of America's current energy situation? The National Academies, advisers to the nation on science, engineering, and medicine, provides objective information about the United States' current energy sources and uses, as well as a look forward to the future of energy.

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Coal

America has plenty of coal. Its mines produced about 900 million tons in 2015, nearly all of it destined for domestic electricity generation, but also some for export. That is only a tiny fraction of U.S. recoverable coal reserves, which are estimated at about 257 billion tons. In fact, more than one-fourth of the world's total known coal reserves are located in the United States. Despite the magnitude of those resources, questions have recently been raised about how accessible these reserves truly are. The location, quality, and recoverability of the coal could significantly impact these supply estimates and experts caution that the reserves should be analyzed more closely with these factors in mind.

More than one-fourth of the total known world coal reserves are in the United States.

Coal consumption in the United States is projected to decrease slightly during the next 25 years, from 801 million tons in 2015 to 557 million tons by 2040-about 1.4% per year. But federal and state policies governing permissible emissions from power plants may change, affecting the way coal is used. In addition, competing energy sources for electricity generation could reduce the demand for coal. Future increases in the supply will probably come from western states because of the low sulfur content of the resource in that region, which now provides about 57% of the nation's coal. Wyoming alone typically accounts for about 42% of all domestic coal mined.

Of all the fossil-fuel sources, coal is the least expensive for its energy content and is a major factor in the cost of electricity in the United States. However, burning coal in electric power plants is a major source of carbon dioxide (CO2) emissions, and its use has other repercussions as well. Mining coal disturbs the land and modifies the chemistry of rainwater runoff, which in turn affects stream and river water quality. It also releases substantial amounts of methane, a potent greenhouse gas. The U.S. Environmental Protection Agency's Clean Power Plan, as well as the low cost of natural gas, is leading older coal plants to close and reducing interest in new coal plants.

Coal-fired power plant combustion gases pass through " scrubbers" and other technologies that remove pollutants before they exit the smokestack. Even so, the smoke contains oxides of nitrogen and sulfur dioxide that lead to smog and acid rain, particulate matter such as soot, and heavy metals such as mercury that affect air quality and human health, often even hundreds of miles from the power plant. In response to recent environmental laws, advanced technologies-often termed " clean coal "-are being developed to further reduce harmful emissions and improve the efficiency of these plants.

For more information, see the U.S. Environmental Protection Agency's Clean Power Plan.

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The National Academies presents: What You Need to Know About Energy

# data[].attributes.attachment_link.description
Want to understand the basics of America's current energy situation? The National Academies, advisers to the nation on science, engineering, and medicine, provides objective information about the United States' current energy sources and uses, as well as a look forward to the future of energy.

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Nuclear

The ability to control nuclear fission reactions, in which atoms of radioactive elements such as uranium split apart into smaller atoms and liberate energy in the process, represents one of the great technological feats of the twentieth century. Harnessed as heat, the released energy boils water, producing steam that drives turbines, thereby being converted to mechanical energy that generates electricity. Nuclear energy currently provides 20% of total electricity generation in the United States and 9.5% of total energy consumed.

Nuclear energy currently provides 20% of total electricity generation in the United States.

According to the U.S. Energy Information Administration's 2015 estimates, output from nuclear power plants is expected to remain flat through 2040. Nuclear capacity could decline by as much as 30% by 2035 unless existing plants are updated, licenses are extended, or new plants are constructed and operated in the very near future. Four reactors were removed from service in 2013 and one entered service in 2014, leaving a total of 60 commercially operating plants (with 100 reactors) in 30 states as of 2015. But of those, 72 reactors received license renewals that allow longer operation. And in 2015 four new plants were under construction and proposals for eight more were under review by the Nuclear Regulatory Commission.

In 2015, U.S. commercial nuclear power reactors bought 56.5 million pounds of uranium from both domestic and foreign suppliers; domestic production accounted for only 3% of that total. According to the International Atomic Energy Agency, worldwide identified resources totaled about 7.6 million metric tons in 2014. If there is renewed U.S. interest in nuclear fission power generation, sufficient uranium supplies will likely be available.

Some countries have made substantial commitments to nuclear power generation: For example, nuclear power plants produce more than three-quarters of all electricity in France. In the United States, the issue prompts considerable debate, including concern about plant safety (which has been strong since the 1979 Three Mile Island accident), security (keeping nuclear material out of the hands of criminals), and arguments about where and how to dispose of nuclear waste, a contentious issue that remains unresolved after decades of effort. Additionally, the low cost of natural gas is making it more difficult for nuclear power to compete in U.S. energy markets.

According to the Congressional Research Service, as of December 2011, there were more than 67,000 metric tons of spent nuclear fuel (SNF) from U.S. reactors in "interim" storage at 77 sites in the United States (including four U.S. Department of Energy facilities), increasing at a rate of roughly 2,000 metric tons per year. At present, there is no plan to store this SNF at any permanent waste site.

Many countries re-process SNF from commercial reactors to increase its radioactive content, although the United States does not.

Another nuclear energy source, fusion, is the process that powers the Sun and the stars. In theory, it could offer a virtually unlimited supply of energy with significantly reduced quantities of long-lived radioactive waste compared to fission, if successfully harnessed in a reactor. To date, several large new research facilities have been built to investigate alternative technologies for generating energy from fusion. Although continuous progress is being made, none of the facilities has achieved "ignition," the point at which a fusion reaction sustains itself, despite decades of research. Absent a significant breakthrough, fusion reactors are unlikely to be ready for commercial deployment in the foreseeable future.

# data[].attributes.attachment_link.title
The National Academies presents: What You Need to Know About Energy

# data[].attributes.attachment_link.description
Want to understand the basics of America's current energy situation? The National Academies, advisers to the nation on science, engineering, and medicine, provides objective information about the United States' current energy sources and uses, as well as a look forward to the future of energy.

# data[].attributes.attachment_link.title
The National Academies presents: What You Need to Know About Energy

# data[].attributes.attachment_link.description
Want to understand the basics of America's current energy situation? The National Academies, advisers to the nation on science, engineering, and medicine, provides objective information about the United States' current energy sources and uses, as well as a look forward to the future of energy.

# data[].attributes.attachment_link.title
The National Academies presents: What You Need to Know About Energy

# data[].attributes.attachment_link.description
Want to understand the basics of America's current energy situation? The National Academies, advisers to the nation on science, engineering, and medicine, provides objective information about the United States' current energy sources and uses, as well as a look forward to the future of energy.

# data[].attributes.attachment_link.title
The National Academies presents: What You Need to Know About Energy

# data[].attributes.attachment_link.description
Want to understand the basics of America's current energy situation? The National Academies, advisers to the nation on science, engineering, and medicine, provides objective information about the United States' current energy sources and uses, as well as a look forward to the future of energy.

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Nuclear energy is released from the nucleus of atoms through the processes of fission or fusion.

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Coal is a combustible black or dark brown rock consisting of carbonized plant matter, found mainly in underground deposits and widely for electricity production.

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Solar energy refers to technologies that convert the sun's heat or light to another form of energy for use.

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Wind Energy refers to technology that converts the air's motion into mechanical energy usually for electricity production.

WIND Energy
Definition
Wind Energy captures the natural wind in our environment and converts the air's motion into mechanical energy. Wind is caused by differences in atmospheric pressure. Wind speeds vary based on geography, topography and season. As a result, there are some locations better suited for wind energy generation than others. In general, wind speeds are higher near the coast and offshore since there are fewer objects like vegetation, mountains and buildings to slow them down. Origin of winds. (2010). Retrieved from the National Weather Servicehttp://www.srh.noaa.gov/jetstream//synoptic/wind.htm NASA Surface Meteorology and Solar Energy. Global Wind Speeds. (2001). Retrieved from http://earthobservatory.nasa.gov/IOTD/view.php?id=1824 NASA Surface Meteorology and Solar Energy. Global Wind Speeds. (2001). Retrieved from http://earthobservatory.nasa.gov/IOTD/view.php?id=1824 NASA Surface Meteorology and Solar Energy. Global Wind Speeds. (2001). Retrieved from http://earthobservatory.nasa.gov/IOTD/view.php?id=1824 NASA Surface Meteorology and Solar Energy. Global Wind Speeds. (2001). Retrieved from http://earthobservatory.nasa.gov/IOTD/view.php?id=1824 Origin of winds. (2010). Retrieved from the National Weather Servicehttp://www.srh.noaa.gov/jetstream//synoptic/wind.htm Origin of winds. (2010). Retrieved from the National Weather Servicehttp://www.srh.noaa.gov/jetstream//synoptic/wind.htm Origin of winds. (2010). Retrieved from the National Weather Servicehttp://www.srh.noaa.gov/jetstream//synoptic/wind.htm

The mechanism used to convert air motion into electricity is referred to as a turbine. A turbine is a large structure with several spinning blades. These blades are connected to an electro-magnetic generator that generates electricity when the wind causes the blades to spin.
Context
Traditionally, this energy was used for milling grain and pumping water, but today it is most commonly used to create electricity. Wind energy is becoming an increasingly important part of the global electricity supply mix. The International Panel on Climate Change. (2011). Potential of Renewable Energy Outlined in Report by the Intergovernmental Panel on Climate Change. Retrieved fromhttp://www.ipcc.ch/news_and_events/docs/ipcc33/PRESS%20RELEASE%20Updated%20version%20-%20Potential%20of%20Renewable%20Energy%20Outline.pdf The International Panel on Climate Change. (2011). Potential of Renewable Energy Outlined in Report by the Intergovernmental Panel on Climate Change. Retrieved fromhttp://www.ipcc.ch/news_and_events/docs/ipcc33/PRESS%20RELEASE%20Updated%20version%20-%20Potential%20of%20Renewable%20Energy%20Outline.pdf The International Panel on Climate Change. (2011). Potential of Renewable Energy Outlined in Report by the Intergovernmental Panel on Climate Change. Retrieved fromhttp://www.ipcc.ch/news_and_events/docs/ipcc33/PRESS%20RELEASE%20Updated%20version%20-%20Potential%20of%20Renewable%20Energy%20Outline.pdf The International Panel on Climate Change. (2011). Potential of Renewable Energy Outlined in Report by the Intergovernmental Panel on Climate Change. Retrieved fromhttp://www.ipcc.ch/news_and_events/docs/ipcc33/PRESS%20RELEASE%20Updated%20version%20-%20Potential%20of%20Renewable%20Energy%20Outline.pdf

A major advantage of wind is that it is a clean and renewable form of energy. Its production of electricity has no direct carbon emissions or air pollutants and does not consume water. Wind also has relatively low operations and maintenance costs after initial construction.

However, wind energy also faces several challenges. Wind speeds can vary throughout the day and year, causing intermittency issues for power grids.

The price tag of wind power has traditionally been higher than conventional electricity generation sources, though the wind cost curve has declined significantly in recent years. NIMBY concerns such as land use, noise, and bird disruption have also been raised in certain areas.

References

1. ^ Origin of winds. (2010). Retrieved from the National Weather Servicehttp://www.srh.noaa.gov/jetstream//synoptic/wind.htm

2. ^ NASA Surface Meteorology and Solar Energy. Global Wind Speeds. (2001). Retrieved from http://earthobservatory.nasa.gov/IOTD/view.php?id=1824

3. ^ The International Panel on Climate Change. (2011). Potential of Renewable Energy Outlined in Report by the Intergovernmental Panel on Climate Change. Retrieved fromhttp://www.ipcc.ch/news_and_events/docs/ipcc33/PRESS%20RELEASE%20Updated%20version%20-%20Potential%20of%20Renewable%20Energy%20Outline.pdf

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Wind Energy refers to technology that converts the air's motion into mechanical energy usually for electricity production. Definition Wind Energy captures the natural wind in our environment and converts the air's motion into mechanical energy. Wind is caused by differences in atmospheric pressure. Wind speeds vary based on geography, topography and season.

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Read p. 279-284. There are practice problems here too to check your understanding.