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Non-Hydroelectric Renewable Energy
Electricty Generation Technologies
Electricity from Non-Hydroelectric Renewable Energy Sources
Non-hydroelectric renewable energy refers to electricity supplied from the following renewable sources of power: solar, geothermal, biomass, landfill gas, and wind. Although installation of these renewable energy resources is growing, non-hydro renewable energy is currently responsible for less than two percent of the electricity generation in the United States.
Air emissions associated with generating electricity from solar, geothermal, and wind technologies are negligible because no fuels are combusted in these processes. The average air emissions rates in the United States from non-hydro renewable energy generation are 1.22lbs/MWh of sulfur dioxide and 0.06 lbs/MWh of nitrogen oxides.1
The sources discussed below are considered to be renewable because they are continuously being replenished. They are also considered to be sustainable because nature will replenish these sources into the future and faster than they can be used.
Solar
About This Technology
Solar energy is a renewable resource because it is continuously supplied to the earth by the sun. There are two common ways to convert solar energy into electricity: photovoltaic and solar-thermal technologies. Photovoltaic systems consist of wafers made of silicon or other conductive materials. When sunlight hits the wafers, a chemical reaction occurs, resulting in the release of electricity. Solar-thermal technologies concentrate the sun's rays with mirrors or other reflective devices to heat a liquid to create steam, which is then used to turn a generator and create electricity.
Reserves
Solar resources are available everywhere in the United States, although some areas receive less sunlight than others, depending on the climate and seasons. The greatest solar resources are located in the Southwestern states, where sufficient solar energy falls on an area of 100 miles by 100 miles to provide all of the nation's electricity requirements.2
Environmental Impacts
Air Emissions
Emissions associated with generating electricity from solar technologies are negligible because no fuels are combusted.
Water Resource Use
Photovoltaic systems do not require the use of any water to create electricity. Solar-thermal technologies may tap local water resources if the liquid that is being heated to create steam is water. In this case, the water can be re-used after it has been condensed from steam back into water.
Water Discharges
Solar technologies do not discharge any water while creating electricity.
Solid Waste Generation
Solar-thermal technologies do not produce any substantial amount of solid waste while creating electricity. The production of photovoltaic wafers creates very small amounts of hazardous materials that must be handled properly to avert risk to the environment or to people.
Land Resource Use
Photovoltaic systems require a negligible amount of land area because they are typically placed on existing structures. In contrast, solar-thermal technologies may require a significant amount of land, depending upon the specific solar-thermal technology used. Solar energy installations do not usually damage the land they occupy, but they prevent it from being used for other purposes. In addition, photovoltaic systems can negatively affect wildlife habitat because of the amount of land area the technology requires.
Geothermal
About This Technology
Geothermal energy is continuously created beneath the Earth's surface from the extreme heat contained in liquid rock (called magma) within the Earth's core. When this heat naturally creates hot water or steam, it can be piped to the surface and then used to turn a steam turbine to generate electricity. Geothermal energy can also be obtained by piping water underground to extract heat from hot, dry rocks. Heat is then returned to the surface to turn a steam turbine and generate electricity.
Reserves
Although geothermal energy exists everywhere in the United States, it is not easy to extract unless it is close to the surface. Some areas of the United States with the greatest potential for generating electricity from geothermal energy include portions of Nevada, California, Oregon, Idaho, Utah, Washington, Alaska, Montana, Arizona, and Hawaii. In 2003, geothermal capacity was 2,300 MW. Currently identified resources could provide more than 20,000 MW of power in the United States, and undiscovered resources might provide five times that amount.3
Environmental Impacts
Air Emissions
Emissions associated with generating electricity from geothermal technologies are negligible because no fuels are combusted.
Water Resource Use
Geothermal power plants usually re-inject the hot water that they remove from the ground back into wells. However, a small amount of water used by geothermal plants in the process of creating electricity may evaporate and therefore not be returned to the ground. Also, for those geothermal plants that rely on hot, dry rocks for energy, water from local resources is needed to extract the energy from the dry rocks.
Water Discharges
Geothermal power plants can possibly cause groundwater contamination when drilling wells and extracting hot water or steam. However, this type of contamination can be prevented with proper management techniques. In addition, geothermal power plants often re-inject used water back into the ground (through separate wells) instead of discharging the used water into surface waters. This prevents underground minerals or pollutants from being introduced into surface waters.
Solid Waste Generation
Geothermal technologies do not produce a substantial amount of solid waste while creating electricity.
Land Resource Use
Geothermal power plants typically require the use of less land than fossil fuel power plants. However, if water is not re-injected into the ground after use to maintain pressure underground, it may cause sinking of land at the surface.
Biomass
About This Technology
The term "biomass" can describe many different fuel types from such sources as trees; construction, wood, and agricultural wastes; fuel crops; sewage sludge; and manure. Agricultural wastes include materials such as corn husks, rice hulls, peanut shells, grass clippings, and leaves. Trees and fuel crops (i.e., crops specifically grown for electricity production) can be replaced on a short time scale.
Agricultural wastes, sewage sludge, and manure are organic wastes that will continue to be produced by society. For these reasons, biomass is considered a renewable resource.
Biomass obtains its energy from the sun while plants are growing. Plants convert solar energy into chemical energy during the process of photosynthesis. This energy is released as heat energy when the plant material is burned. Biomass power plants burn biomass fuel in boilers. The heat released from this process is used to heat water into steam to turn a steam turbine to create electricity.
Biomass is sometimes burned in combination with coal in boilers at power plants. This process, called co-firing, is typically used to reduce air emissions and other environmental impacts from burning coal. Co-firing biomass with coal may require a coal boiler to be modified somewhat so it can combust coal. When co-fired with coal, only a small amount of biomass is typically added (no more than 15 percent of the total amount of fuel going into the boiler) to maintain the boiler's efficiency.4
The paper Biodiesel Production from Municipal Sewage Sludges (PDF) (4 pp., 663K, About PDF) provides detailed information about biodiesel as a fuel derived from renewable biomass.
Reserves
Of the estimated U.S. biomass resource of 590 million net tons, only 14 million dry tons, or enough to supply about 3,000 MW of capacity, is currently available.5
Environmental Impacts
Air Emissions
Biomass power plants emit nitrogen oxides and a small amount of sulfur dioxide. The amounts emitted depend on the type of biomass that is burned and the type of generator used. Although the burning of biomass also produces carbon dioxide, the primary greenhouse gas, it is considered to be part of the natural carbon cycle of the earth. The plants take up carbon dioxide from the air while they are growing and then return it to the air when they are burned, thereby causing no net increase.
Biomass contains much less sulfur and nitrogen than coal;6 therefore, when biomass is co-fired with coal, sulfur dioxide and nitrogen oxides emissions are lower than when coal is burned alone.7 When the role of renewable biomass in the carbon cycle is considered, the carbon dioxide emissions that result from co-firing biomass with coal are lower than those from burning coal alone.8
Water Resource Use
Biomass power plants require the use of water, because the boilers burning the biomass need water for steam production and for cooling. If this water is used over and over again, the amount of water needed is reduced. Whenever any type of power plant removes water from a lake or river, fish and other aquatic life can be killed, which then affects those animals and people that depend on these aquatic resources.
Water Discharges
As is the case with fossil fuel power plants, biomass power plants have pollutant build-up in the water used in the boiler and cooling system. The water used for cooling is much warmer when it is returned to the lake or river than when it was removed. Pollutants in the water and the higher temperature of the water can harm fish and plants in the lake or river where the power plant water is discharged. This discharge usually requires a permit and is monitored. For more information about these regulations, visit EPA's Office of Water Web site. In general, crops grown for biomass fuel require fewer pesticides and fertilizers than crops grown for food, which means that less pesticide and fertilizer runoff will reach local streams and ponds than if food crops are grown.
Solid Waste Generation
The burning of biomass in boilers creates a solid waste called ash that must be disposed of properly. However, the ash from biomass normally contains extremely low levels of hazardous elements.
Land Resource Use
Generating electricity from biomass can affect land resources in different ways. Biomass power plants, much like fossil fuel power plants, require large areas of land for equipment and fuel storage. If these biomass plants burn a waste source such as construction wood waste or agricultural waste, they can provide a benefit by freeing areas of land that might otherwise have been used for landfills or waste piles. Biomass grown for fuel purposes requires large areas of land and, over time, can deplete the soil of nutrients. Fuel crops must be managed so that they stabilize the soil, reduce erosion, provide wildlife habitat, and serve recreational purposes.
Landfill gas
About This Technology
Landfill gas is created when microorganisms cause organic waste, such as food wastes and paper, to decompose in landfills. Landfill gas is composed of about fifty percent methane. Carbon dioxide and volatile organic compounds (VOCs) make up the remainder. Landfill gas escapes into the air unless it is collected and burned. In landfill gas energy projects, landfill gas is burned in boilers, reciprocating engines, and combustion turbines to produce electricity. The landfill size and age, quantity of organic waste, and the local climate help determine how much gas a landfill can produce. EPA requires large landfills to collect and burn landfill gas with flares to destroy the VOCs.
Reserves
While some landfills simply burn landfill gas with a flare, more than 380 projects at 365 U.S. landfills are collecting and using landfill gas to produce energy.9 Thirty additional projects are currently under construction. EPA estimates that more than 600 additional landfills could support landfill gas energy projects cost-effectively.10 Landfill gas continues to be produced for twenty years or more after a landfill is closed. Therefore, as long as landfills continue to be built, landfill gas will continue to be a resource for producing electricity.
Environmental Impacts
Air Emissions
Burning landfill gas produces nitrogen oxides emissions as well as trace amounts of toxic materials. The amount of these emissions can vary widely, depending on the waste from which the landfill gas was created. The carbon dioxide released from burning landfill gas is considered to be a part of the natural carbon cycle of the earth. Producing electricity from landfill gas avoids the need to use non-renewable resources to produce the same amount of electricity. In addition, burning landfill gas prevents the release of methane, a potent greenhouse gas, into the atmosphere.
Water Resource Use
Engines or combustion turbines that burn landfill gas to produce energy typically require negligible amounts of water.
Water Discharges
Engines and combustion turbines burning landfill gas have very little or no water discharges. The collection of landfill gas involves drilling wells into landfills, which does not affect local bodies of water.
Solid Waste Generation
Landfill gas technologies do not produce any substantial amount of solid waste while creating electricity.
Land Resource Use
Burning landfill gas to produce electricity has little impact on land resources. While the equipment used to burn the landfill gas and generate electricity does require space, it can be located on land already occupied by the existing landfill, thus avoiding any additional use of land.
Wind
About This Technology
Wind is created because the sun heats the Earth unevenly, due to the seasons and cloud cover. This uneven heating, in addition to the Earth's rotation, causes warmer air to move toward cooler air. This movement of air is wind.
Wind turbines use two or three long blades to collect the energy in the wind and convert it to electricity. The blades spin when the wind blows over them. The energy of motion contained in the wind is then converted into electricity as the spinning turbine blades turn a generator. To create enough electricity for a town or city, several wind turbine towers need to be placed together in groups or rows to create a "wind farm."
Reserves
The availability of wind power varies across the United States. Areas with the best wind availability include portions of the following states: North Dakota, Texas, Kansas, South Dakota, Montana, Nebraska, Wyoming, Oklahoma, Minnesota, Iowa, Colorado, New Mexico, California, Wisconsin, and Oregon. In general, wind is consistent and strong enough in the Great Plains states and mountain passes in the various mountain ranges throughout the United States to generate electricity using wind turbines. The Rocky Mountain and Great Plains states have sufficient wind resources to meet 10 to 25 percent of the electric power requirements of these states.11
Environmental Impacts
Air Emissions
Emissions associated with generating electricity from wind technology are negligible because no fuels are combusted.
Water Resource Use
Wind turbines in areas with little rainfall may require the use of a small amount of water. If rainfall is not sufficient to keep the turbine blades clean, water is used to clean dirt and insects off the blades so that turbine performance is not reduced.
Water Discharges
Wind turbines do not discharge any water while creating electricity.
Solid Waste Generation
Wind technologies do not produce any substantial amount of solid waste while creating electricity.
Land Resource Use
Wind turbines generally require the use of land, although they may also be sited offshore. Land around wind turbines can be used for other purposes, such as the grazing of cattle or farming.
When wind turbines are removed from land, there are no solid wastes or fuel residues left behind. However, large wind farms pose aesthetic concerns and wind turbines that are improperly installed or landscaped may create soil erosion problems. Wind farms can also have noise impacts, depending on the number of wind turbines on the farm. New blade designs are being used to reduce the amount of noise. Bird and bat mortality has been an issue at some wind farms. Improvements to wind turbine technologies and turbine siting have helped mitigate bird mortality. Research on impacts to bats is now underway.12
- U.S. EPA, Compilation of Air Pollutant Factors (AP-42).
- U.S. Department of Energy, Energy Efficiency and Renewable Energy Network, Geothermal Energy Program, CSP Technologies Overview.
- U.S. Department of Energy, National Renewable Energy Laboratory, The Status and Future of Geothermal Electric Power, 2000 (PDF) (9 pp., 472K, About PDF).
- U.S. Department of Energy, Energy Efficiency and Renewable Energy Clearinghouse, Biomass Cofiring: A Renewable Alternative for Utilities. June 2000. DOE/GO-102000-1055.
- U.S. Department of Energy, Energy Information Administration, Biomass for Electricity Generation.
- U.S. Department of Energy, Energy Efficiency and Renewable Energy Clearinghouse, Biomass Cofiring: A Renewable Alternative for Utilities. June 2000. DOE/GO-102000-1055.
- Ibid.
- Ibid.
- U.S. EPA Landfill Methane Outreach Program.
- Ibid.
- National Wind Technology Center, D.L. Elliott and M.N. Schwartz. Wind Energy Potential in the United States. September 1993.
- American Wind Energy Association
.