Where does our electricity come from?
Generating electricity is a miracle of modern technology. Acting more or less like a force field, electric current is comprised of minuscule protons and electrons that become charged when induced by friction or chemical changes. Most power plants burn fuel – coal, oil, natural gas, biomass – which creates steam to drive a turbine that generates electricity. Sometimes nuclear or solar energy creates the steam to drive the turbine. Other technologies – such as solar photovoltaics or fuel cells – rely upon chemical reactions to generate electricity.
For specifics, select any of these technologies:
1. Electricity from: Biomass
The term “biomass” encompasses diverse fuels derived from timber, agriculture and food processing wastes or from fuel crops that are specifically grown or reserved for electricity generation. Biomass fuel can also include sewage sludge and animal manure. Some biomass fuels are derived from trees. Given the capacity of trees to regenerate, these fuels are considered renewable. Burning crop residues, sewage or manure – all wastes that are continually generated by society — to generate electricity may offer environmental benefits in the form of preserving precious landfill space OR may be grown and harvested in ways that cause environmental harm.
At present, most biomass power plants burn lumber, agricultural or construction/demolition wood wastes. Direct Combustion power plants burn the biomass fuel directly in boilers that supply steam for the same kind of steam-electric generators used to burn fossil fuels. With biomass gasification, biomass is converted into a gas – methane – that can then fuel steam generators, combustion turbines, combined cycle technologies or fuel cells. The primary benefit of biomass gasification, compared to direct combustion, is that extracted gasses can be used in a variety of power plant configurations.
In terms of capacity, biomass power plants represent the second largest amount of renewable energy in the nation.
Because biomass technologies use combustion processes to produce electricity, they can generate electricity at any time, unlike wind and most solar technologies, which only produce when the wind is blowing or sun is shining. Biomass power plants currently represent 11,000 MW – the second largest amount of renewable energy in the nation.
What are the environmental impacts?
Whether combusting directly or engaged in gasification, biomass resources do generate air emissions. These emissions vary depending upon the precise fuel and technology used. If wood is the primary biomass resource, very little SO2 comes out of the stack. NOx emissions vary significantly among combustion facilities depending on their design and controls. Some biomass power plants show a relatively high NOx emission rate per kilowatt hour generated if compared to other combustion technologies.
This high NOx rate, an effect of the high nitrogen content of many biomass fuels, is one of the top air quality concerns associated with biomass.
Carbon monoxide (CO) is also emitted – sometimes at levels higher than those for coal plants.
Biomass plants also release carbon dioxide (CO2), the primary greenhouse gas. However, the cycle of growing, processing and burning biomass recycles CO2 from the atmosphere. If this cycle is sustained, there is little or no net gain in atmospheric CO2. Given that short rotation woody crops (i.e., fast growing woody plant types) can be planted, matured and harvested in shorter periods of time than natural growth forests, the managed production of biomass fuels may recycle CO2 in one-third less time than natural processes.
Biomass power plants also divert wood waste from landfills, which reduces the productions and atmospheric release of methane, another potent greenhouse gas.
Another air quality concern associated with biomass plants is particulates. These emissions can be readily controlled through conventional technologies. To date, no biomass facilities have installed advanced particulate emission controls. Still, most particulate emissions are relatively large in size. Their impacts upon human health remain unclear.
The collection of biomass fuels can have significant environmental impacts. Harvesting timber and growing agricultural products for fuel requires large volumes to be collected, transported, processed and stored. Biomass fuels may be obtained from supplies of clean, uncontaminated wood that otherwise would be landfilled or from sustainable harvests. In both of these fuel collection examples, the net environmental plusses of biomass are significant when compared to fossil fuel collection alternatives. On the other hand, the collection, processing and combustion of biomass fuels may cause environmental problems if, for example, the fuel source contains toxic contaminants, agricultural waste handling pollutes local water resources, or burning biomass deprives local ecosystems of nutrients that forest or agricultural waste may otherwise provide.
Natural Resources Defense Council Biomass Fact Sheet
Renewable Energy Policy Project Biomass FAQs
NREL’s Biomass Power Project
Northeast Regional Biomass Program
American Bioenergy Association
Union of Concerned Scientists – USA: How Biomass Works
2. Electricity from Coal
Coal is the solid end-product of millions of years of decomposition of organic materials. In truth, coal is stored solar energy. Plants capture the energy from sunlight through photosynthesis, which directly converts solar energy to plant matter. Animals that then eat the plants to convert that energy again, storing it in their own bodies.
Over millions of years, accumulated plant and animal matter is covered by sediment and stored within the earth’s crust, gradually being transformed into hard black solids by the sheer weight of the earth’s surface. Coal, like other fossil fuel supplies, takes millions of years to create, but releases its stored energy within only a few moments when burned to generate electricity. Because coal is a finite resource, and cannot be replenished once it is extracted and burned, it cannot be considered a renewable resource.
The nation’s fleet of over 100 coal plants is responsible for 57 percent of the electricity generated in the U.S., more than any other single electricity fuel source.
Coal is typically burned to create steam, which is then piped at high pressure over a turbine, causing it to rotate, producing electricity. This steam electric system is a common one also used with other fuel sources, including oil, natural gas, geothermal, biomass, and even some solar-fueled systems.
What are the environmental issues?
The popularity of coal is largely due to its low cost.
Nevertheless, coal power plants are responsible for 93 percent of the sulfur dioxide and 80 percent of the nitrogen oxide emissions generated by the electric utility industry.
These emissions spawn the acid rain that is eating away red spruce forests in the Northeast and Appalachia, and rob previously pristine streams of brook trout and other fish species in the Adirondacks, upper Midwest and Rocky Mountains.
Coal emissions also cause urban smog, which has been linked to respiratory ailments, and coal-fired power plants also contribute to global climate change. Coal plants emit 73 percent of the carbon dioxide emitted into the atmosphere from electricity generators. By releasing the energy stored in coal, large quantities of carbon dioxide that have been stored in the coal for millions of years are released back into the atmosphere, increasing the threat of global warming. Coal plants are also a major source of airborne emissions of mercury, a toxic heavy metal.
Federal law requires that air pollution be kept within limits. However, these limits are significantly lower for older coal plants than for newer ones. Even when kept within the air emission limits set by the Clean Air Act, state-of-the-art coal power plants still produce significant damage to human health, public and private property, and ecosystems.
The mining, processing, and transporting of coal also insults the environment. In the West, about 87 percent of coal is removed from the earth through strip mining, which can contaminate soils with heavy metals and destroy near-surface aquifers. In the East, coal is sometimes mined by removing entire mountain tops to more easily extract the subsurface mineral reserves.
Coal combustion also results in huge quantities of solid wastes. Enormous quantities of waste heat require large amounts of water for cooling. The collection of this water from major water bodies threatens local aquatic life, including the killing of fish on the screens designed to keep such organisms out of the power plant.
U.S. Dept. of Energy’s Energy Information Administration (EIA): “Coal Information at a Glance” http://www.eia.doe.gov/fuelcoal.html
Union of Concerned Scientists – USA: Coal
3. Electricity from: Geothermal Energy
The heat from the earth’s own molten core can be converted into electricity. This core consists primarily of extremely high temperature liquid rock known as magma. This “geothermal” heat circulates within the rock or is transferred to underground reservoirs of water, which also circulate under the earth’s crust. Because of the near limitless ability of the earth to produce magma, and the continuous transfer of heat between subsurface rock and water, geothermal energy is considered a renewable resource.
Geothermal resources have been harnessed as an energy source since the dawn of civilization, when natural hot springs were first used for cooking and bathing. The geothermal resources tapped to generate electricity are far more intense than those used for space heating and can reside as deep as 10,000 feet below the earth’s surface. Capital costs for the construction of geothermal power plants are much higher than for large coal-fired plants or new natural gas turbine technologies. But geothermal plants have reasonable operation and maintenance costs and no fuel costs. Though more expensive than wind power in most cases, new geothermal electricity generation facilities are increasingly competitive with fossil options.
Geothermal plants can operate around-the-clock, which increases their value from a reliability point-of-view, unlike some intermittent renewable fuels such as solar and wind.
Geothermal electricity generation technologies consist of either “flash” technology or “binary” technology. With flash technology, water from 300 to 700 degrees Fahrenheit, but still in liquid form, is piped from its highly pressurized underground reservoir into a geothermal facility. Once this super-heated water is released, it flashes into steam that then drives a conventional turbine generator. With binary technology, underground reservoir waters of lower temperatures are used for flashing. Heat from geothermal water is transferred to a second (binary) liquid, which flashes into vapor upon heating, and that vapor is used to drive turbines. (With dry steam technologies – a much rarer fuel source but the one used in the world’s largest geothermal power plant at The Geysers in northern California — highly pressurized geothermal vapor is used directly to drive a turbine.)
What are the environmental impacts?
Flash technologies allow the geothermal fluid to expand and release gases into the atmosphere when the steam is created. Binary technology keeps the geothermal fluid contained, using heat exchangers to capture heat to provide steam. Though these air emissions represent tiny quantities and generally do not pose any serious environmental threat, the chemical characteristics of geothermal resources are highly site-specific. Dissolved gases usually include carbon dioxide (CO2), methane, hydrogen sulfide, ammonia, nitrogen and hydrogen.
Groundwater contamination, which can be easily prevented, is the principal pollution concern.
The disposal of water and wastewater may cause significant pollution of surface waters and ground water supplies. Still, used geothermal fluids are generally collected and re-injected. This maintains pressures in underground reservoirs, but also allows for recycling and reuse.
The best geothermal resources are sometimes located at remote sites that may have significant wilderness, scenic or recreation value. While requiring relatively little land itself, the siting of a geothermal plant – like remote wind farms — may cause land impacts when new transmission lines are connected to power plants in these rural regions.
U.S. Department of Energy – Geothermal Power
Idaho National Engineering and Environmental Laboratory (INEEL) – Geothermal Program
Geothermal Resources Council
Geothermal Resource Information Clearinghouse
Union of Concerned Scientists – USA: Geothermal
4. Electricity from: Hydro
Harnessing the force of falling water may be the world’s oldest source of mechanical power. Hydropower currently supplies 10 percent of the nation’s electricity and 80 percent of the electricity now produced from renewable resources.
Normally, rain water and melting snow flows by gravity, producing streams, rivers, and lakes. Hydropower facilities intercept the water on its downward path, converting its mechanical energy into electricity. Because the cycle of water evaporating from the heat of the sun and falling back to earth is continuously renewed by the sun’s energy, hydropower is often considered a renewable energy resource. However, the construction and operation of hydropower dams impact natural river systems and fish and wildlife. Whether specific hydropower projects create unacceptable environmental damage requires a case-by-case review.
There are several types of hydropower facilities:
- “Storage” projects impound water behind a dam, forming a reservoir. Water is released through turbine-generators to produce electricity. The water storage and release cycles can be relatively short, for instance, storing water at night for daytime power generation. Or, the cycles can be long, storing spring runoff for generation in the summer when air conditioner use increases power demand. Some projects operate on multi-year cycles carrying over water in a wet year to offset the effects of dry years.
- “Run-of-river” projects typically use relatively low dams where the amount of water running through the powerhouse is determined by the water flowing in the river. Because these plants generally do not hold back water behind storage dams, they tend to affect upstream water levels and downstream stream flow less than storage projects. Electricity generation from these plants will vary with changes in the amount of water flowing in the river.
- “Pumped-storage” projects use off-peak electricity to pump water from a lower reservoir to an upper reservoir. During periods of high electrical demand, the water is released back to the lower reservoir to generate electricity. There are only about 40 pumped-storage facilities in the U.S., but some are very large. (Note: the Power Scorecard rates electricity from pumped storage on the basis of the electricity used to pump the water and the impacts of the storage operations.)
What are the environmental impacts?
It is the dams and powerhouse operations essential to hydropower plants that cause the primary environmental impacts. The changes in river conditions and the land and vegetation bordering the water bodies caused by dams and powerhouse turbines may impact fish populations and other wildlife significantly. Even small dams can cause big impacts on to the health of regional fish populations. The impacts of large dams are wide-ranging. The impacts of any dam depend upon many important factors, including the location of the dam, the facility design, the sensitivity of the local environment to effects of the hydropower facility, and steps taken to modify the design and/or operation of each facility to reduce potential impacts.
Many impacts (see list below) can be significantly reduced by changing operations of the dam. For example, installing fish passage systems can reduce impacts on migratory fish; and converting a dam from peaking to “run-of-river” operation can ensure the natural flow of the river remains undisturbed and can adapt the hydropower facility to the unique conditions of each river system.
Because every river and every dam are different, the type and severity of impacts caused by each dam differs. Because these potential impacts are severe, it is important to distinguish the plants that have successfully reduced or eliminated specific impacts from those that have not.
Since 1987 the licensing and review process conducted by the Federal government has more thoroughly addressed environmental impacts. Before 1987 the environmental impacts of facilities were considered inconsistently and sometimes not at all. The Power Scorecard recognizes this change in the quality of environmental review by giving a better environmental rating to projects reviewed since January 1987.
Recently the Low Impact Hydropower Institute has created a Low Impact Hydropower Certification program to identify and reward efforts by dam owners to minimize the impacts of their hydropower dams. The program certifies hydropower facilities with impacts that are low compared to other hydropower facilities based on eight environmental criteria:
- river flows
- water quality
- fish passage and protection
- watershed protection
- threatened & endangered species protection
- cultural resource protection
- facilities recommended for removal
The Power Scorecard recognizes plants that have obtained this “low impact certification” by giving them a better environmental rating.
The following paragraphs outline some of the kinds of environmental impacts hydropower plants can create and measures that can be used to mitigate such impacts. The scope and severity of such impacts vary from facility to facility, and depend on site conditions and the extent to which possible mitigation measures are actually used.
Potential environmental impacts
Hydroelectric facilities disrupt natural river flows.
By diverting water out of the river for power, dams remove water needed for healthy in-stream ecosystems. Stretches below dams may be completely de-watered. By withholding and then releasing water to generate power for peak demand periods, dams may cause downstream stretches to alternate between no water and powerful surges that erode soil and vegetation, and flood or strand wildlife. These irregular releases destroy natural seasonal flow variations that trigger natural growth and reproduction cycles in many species. Peaking power operations can also cause can cause dramatic changes in reservoir water levels – up to 40 feet – that can degrade shorelines and disturb fisheries, waterfowl, and bottom?dwelling organisms.
Dams also slow down the flow of the river. Many fish species, such as salmon, depend on steady flows to flush them downriver early in their life and guide them upstream years later to spawn. Slow reservoir pools disorient migrating fish and significantly increase the duration of their migration.
These impacts can, at times, be mitigated by technological and operational enhancements to the hydro project – e.g., minimum flow turbines, re-regulating weirs, and pulsed operation at peak efficiency. Impoundments can be managed to create new upstream and downstream habitat for fish species and to provide minimum discharges and improved habitat during seasonal or annual drought conditions.
Hydropower may alter river and riverside habitat.
Construction of a dam can flood riverside lands, destroying riparian and upland habitats. Construction of a dam can also convert river habitat into a lake-like reservoir, threatening native populations of fish and other wildlife. Warm, slow moving reservoirs favor predators of naturally occurring species. Dramatic changes in reservoir water levels, described above, can degrade shorelines and disturb fisheries, waterfowl, and bottom-dwelling organisms.
Dams alter water quality.
Impoundments can cause changes and variation in temperature or the amount of dissolved gases in the river.
Surface temperatures in the reservoir may rise when the flow of the water is slowed. If water is released from the top of the dam, this warmer water may increase river water temperature down stream. Cooler downstream temperatures may result when cool water is released from the bottom of a reservoir. Such altered conditions can affect the habitat, growth rate, or even the survival of fish and other species.
For hydropower projects with intakes located deep in the reservoir, water with low dissolved oxygen (DO) levels released to the river downstream may harm aquatic habitat in the river and contribute to other water quality problems. Applying mitigating technologies can improve dissolved oxygen levels.
Water sometimes passes over a spillway, rather than through the turbines. As water plunges into the pool at the base of the dam, too much air can be trapped in the water, creating “gas supersaturation,” a condition that in some fish species fosters something called lethal gas bubble disease. This can be mitigated by installing structures to keep fish away from such areas.
A dam or a powerhouse can be a significant obstacle to fish migration.
Ladders or lifts can be installed to pass certain fish species upstream, though multiple dams on a river reduces the success rate of these fish passage devices. Fish migrating downstream can become disoriented, bruised, stressed, or mortally injured from contact with turbines or other parts of the facility. Bypass systems can improve survival rates for migrating juveniles. When fish are trucked or barged around the dams, they may experience increased stress and disease and decreased homing instincts. Survival rates for fish passing through large turbines vary but may approach 90-95 percent. In the case of multiple dams along a river these effects can significantly harm migrating populations of important, sensitive juvenile fish populations.
Impoundments also slow down the flow velocities of rivers. Slow reservoir pools may disorient migrating fish, increase the duration of their migration, which in turn may increase their mortality rate.
The steep decline in salmon populations in the Pacific Northwest and California is perhaps the best known negative environmental impact associated with hydroelectric facilities. Although several factors have affected this decline – including commercial fish harvests, habitat degradation, and artificial fish hatcheries – hydropower dams have contributed significantly. The causes for these declines and the best strategies for restoring these important fisheries are currently the subject of a major public policy debate.
Hydropower projects can impede the natural flow of sediments.
Flowing water transports sediment. When the flow velocities are reduced in an impoundment, sediment drops out and collects on river and reservoir bottoms, where it can affect habitat for fish spawning. The loss of sediment downstream can degrade in stream habitat and cause the loss of beach at the mouth of the river. The deposited sediment also may contain chemical or industrial residues from upstream sources. Dams may block and concentrate contaminated sediment in the impoundment. Dredging is used in some cases, though it is costly and may raise questions regarding disposal of the dredged material. Various flushing and piping techniques are available for moving non-contaminated sediment downstream.
See also Water Use, Water Quality and Land Impacts Issue Papers for more information on hydropower impacts.
Union of Concerned Scientists: “How Hydroelectricity Energy Works”
Low Impact Hydropower Institute
Hydropower Reform Coalition
Idaho National Engineering and Environmental Lab (INEEL)Hydropower Program
National Hydropower Association
U.S. Dept. of Energy – Energy Efficiency and Renewable Energy Network/Hydro Links Page
Foundation for Water and Energy Education (FWEE)
Association of State Dam Safety Officials
Bureau of Reclamation Hydropower Program
Hydro Research Foundation
Northwest Power and Conservation Council – “Guide to Major Hydropower Dams of the Columbia River Basin”
The United States Society on Dams
Wisconsin Valley Improvement Company
World Commission on Dams
5. Electricity from: Landfill Gas
Large municipal or industrial landfills produce gas that can be tapped to generate electricity. Microorganisms that live in organic materials such as food wastes, paper or yard clippings cause these materials to decompose. This produces landfill gas, typically comprised of roughly 60 percent methane and 40 percent carbon dioxide (or “CO2”).
The US Environmental Protection Agency (EPA) requires all large landfills to install collection systems at landfill sites to minimize the release of methane, a major contributor to global climate change. Though not a renewable resource, landfill gas will be in great supply absent major innovations in solid waste management systems and could supply up to 1 percent of the nation’s energy demand.
Landfill gas is collected from landfills by drilling “wells” into the landfills, and collecting the gases through pipes. Once the landfill gas is processed, it can be combined with natural gas to fuel conventional combustion turbines or used to fuel small combustion or combined cycle turbines. Landfill gas may also be used in fuel cell technologies, which use chemical reactions to create electricity, and are much more efficient than combustion turbines.
What are the environmental impacts?
The environmental impacts of landfill gas begin with issues surrounding landfills themselves – land use impacts and surface and groundwater issues. Does reliance on landfills discourage more environmentally preferred waste management substitutes, such as waste reduction, reuse and recycling?
Since the landfill, typically, is sited for other municipal purposes, many of the negative issues associated with landfills themselves are not incorporated in the analysis of landfill gas as a power source.
Use of the gas produced by landfills may reduce the harmful environmental impacts that would otherwise result from landfill operations. Landfill gas electricity generation offers major air quality benefits where landfills already exist or where the decision to build the landfill has already been made.
Landfill gas power plants reduce methane emissions, a global climate change agent with 23 times the negative impact of CO2.
A landfill gas power plant burns a waste – methane — that would otherwise be released into the atmosphere or burned off in a flaring process. Methane is a highly potent agent of global climate change, having about 23 times the negative impact on a pound-by-pound basis as CO2. Landfill gas combustion produces some CO2, but the impact of these emissions on global climate change is offset many times over by the methane emission reductions.
While new EPA regulations require gathering and flaring of methane from large landfill operations, small landfills, which fall outside the federal agency’s jurisdiction, may amount to as much as 40 percent of the methane generated by landfills nationwide.
Landfill gas generators produce nitrogen oxides emissions that vary widely from one site to another, depending on the type of generator and the extent to which steps have been taken to minimize such emissions. Combustion of landfill gas can also result in the release of organic compounds and trace amounts of toxic materials, including mercury and dioxins, although such releases are at levels lower than if the landfill gas is flared.
There are few water impacts associated with landfill gas power plants. Unlike other power plants that rely upon water for cooling, landfill gas power plants are usually very small, and therefore pollution discharges into local lakes or streams are typically quite small.
EPA Fact Sheet: “Powering Microturbines with Landfill Gas”
EPA “LFG Energy Projects: Current Projects and Candidate Landfills”
6. Electricity from: Natural Gas
Natural gas is the generic term used for the mixture of vapors that result from the decomposition of plant and animal materials over millions of years. Natural gas, along with oil and coal, is a fossil fuel and, similar to oil and coal, is found in underground reservoirs located in several areas of North America. The primary component of natural gas is methane, a hydrocarbon.
Natural gas is the cleanest of all the fossil fuels.
The stock of natural gas, like other fossil-based fuels, is limited and is therefore not a renewable resource. The combustion of natural gas produces only a fraction of the nitrogen oxide and carbon dioxide emissions of oil and coal, and also results in essentially no particulate matter or sulfur dioxide emissions. Natural gas therefore becomes an attractive “transition” fuel, as the energy supply moves away from polluting sources such as coal and nuclear sources and towards cleaner, renewable technologies.
Natural gas can be used as a fuel in conventional steam boiler generators, like other fossil fuels. However, new technologies using natural gas as their primary fuel are far more efficient than older combustion technologies. New state of the art combined cycle plants reduce fossil fuel use by as much as 40 percent.
Combustion turbines are based on jet engines. With the combustion turbine technology, the natural gas is burned, creating superheated gas, which is then pressurized in pipes and used to drive the turbine. Combined cycle technology is really the coupling of two electric generation technologies, and boosts efficiency by using the same fuel to generate electricity twice. Natural gas may also be used in fuel cell technologies that rely upon chemical reactions to create electricity at much higher levels of efficiency than can be obtained from fossil fuel combustion.
What are the environmental issues?
Natural gas creates significantly smaller environmental impacts than coal. On a Btu basis, natural gas combustion generates about half as much carbon dioxide, or CO2, as coal, less particulate matter, and very little sulfur dioxide or toxic air emissions. Natural gas combustion may, however, produce nitrogen oxides and carbon monoxide in quantities comparable to coal burning. Ongoing use of natural gas inevitably results in methane emissions, a very potent greenhouse gas contributing to global climate change. Natural gas drilling and exploration can negatively impact wilderness habitat, wildlife and public open space. Among the list of potential negative land impacts associated with natural gas are erosion, loss of soil productivity, increased runoffs, landslides and flooding.
If natural gas is compared to coal combustion, CO2 emissions are significantly reduced, but natural gas combustion still results in a net increase in CO2 emissions and therefore can contribute to climate change.
Gas plant operations may result in significant impacts on water resources, depending on the type of combustion technology and plant design. Combustion turbines do not use significant quantities of water; combined cycle power plants do have a steam-cooling phase that may require significant quantities of water.
U.S. Dept. of Energy’s Energy Information Administration (EIA): “Natural Gas Information at a Glance”
Union of Concerned Scientists:How Natural Gas Works
7. Electricity from: Nuclear Power
Nuclear power plants are fueled by uranium, a naturally-occurring element found in the Rocky Mountains and in countries such as Canada, Australia and South Africa. The nearly infinite energy that is stored in uranium atoms makes nuclear power possible.
The interaction between three “heavy” elements – two types of uranium and a form of plutonium — creates a chain reaction that can be harnessed to generate electricity. The nuclear reaction generates heat that is used to boil water to create steam to drive a turbine to generate electricity. Like fossil fuels, uranium is a finite non-renewable resource.
At present, over a hundred commercial nuclear power reactors operate in 33 states. Still, no new nuclear power reactors have been ordered in over two decades.
What are the environmental impacts?
Some tout nuclear power plants as a “clean” electricity source since the nuclear plants themselves do not release any of the “traditional” power generation air pollutants, such as sulfur dioxide, carbon dioxide or nitrogen oxides. Nevertheless, the requirements for the operation of nuclear power plants result in environmental impacts, including air emissions, at all stages of the uranium fuel procurement process.
While plant operations do not result in air emissions similar to those of fossil plants, nuclear plants can release small amounts of airborne radioactive gasses, such as carbon-14 and iodine-131.
Uranium mining mimics techniques used for coal and similar issues of toxic contamination of local land and water resources arise — as do unique radioactive contamination hazards to mine workers and nearby populations. Abandoned mines contaminated with high-level radioactive waste can continue to pose radioactive risks for as long as 250,000 years after closure.
In the nuclear fuel processing process, the uranium enrichment process depends on great amounts of electricity, most of which is provided by dirty fossil fuel plants releasing all of the traditional air pollution emissions not released by the nuclear reactor itself. Two of the nation’s most polluting coal plants in Ohio and Indiana, for example, produce electricity primarily for uranium enrichment. In addition, the fuel processing produces radioactive wastes, which must be adequately stored and sequestered to minimize the risk of radioactive release.
Nuclear plants that rely upon water for once-through cooling systems require two-and-a-half times as much water as fossil fuel plants. The impact on water resources, aquatic habitats, and fish are therefore more significant with nuclear power plants than any other power generation technology (with the possible exception of hydroelectric facilities themselves). The San Onofre Nuclear Generating Station located in southern California consumes 500 metric tons of croaker and white fish annually, the equivalent catch of seven million recreational fishermen.
Some of the most serious impacts linked to the generation of electricity on land can also be attributed to nuclear plants. Whereas the amount of solid wastes generated at nuclear plants is relatively small, these radioactive wastes pose health risks that exceed that of any other source of electricity. It is quite possible that these radioactive wastes will be stored for a century or more at existing nuclear plant sites, a prospect that may preclude any future re-uses of these contaminated lands.
A major failure in a nuclear power plant’s cooling systems can create a nuclear meltdown, where fuel rods melt within a matter of seconds. The heat from the uncontrolled reaction can melt everything it comes into contact with. Catastrophic accidents could injur or kill thousands of people.
The risk of this type of catastrophic accident, and the subsequent release of massive quantities of radioactive materials, carries severe consequences for all forms of life.
Nuclear Energy Institute
U.S. Dept. of Energy’s Energy Information Administration (EIA): “Nuclear and Uranium Information at a Glance”
Union of Concerned Scientists: How Nuclear Power Works
8. Electricity from Oil
Oil is the largest source of energy in the United States, providing close to 40 percent of all of the nation’s entire power needs. Though most oil is used for transportation or home heating purposes, a small percentage is still used as a fuel for electricity generating plants.
While oil continues to decline in popularity as an electricity fuel, in places such as New York, oil still comprises about 8 percent of the state’s electricity fuel mix.
Oil sits in deep underground reservoirs. Like other fossil fuels, this liquid is the end-product of millions of years of decomposition of organic materials. Since the ultimate amount of oil is finite — and cannot be replenished once it is extracted and burned – it cannot be considered a renewable resource. Once extracted, oil can be refined into a number of fuel products — gasoline, kerosene, liquefied petroleum gas (such as propane), distillates (diesel and jet fuels) and “residuals” that include industrial and electricity fuels.
Three technologies are used to convert oil into electricity:
- Conventional steam – Oil is burned to heat water to create steam to generate electricity.
- Combustion turbine – Oil is burned under pressure to produce hot exhaust gases which spin a turbine to generate electricity.
- Combined-cycle technology – Oil is first combusted in a combustion turbine, using the heated exhaust gases to generate electricity. After these exhaust gases are recovered, they heat water in a boiler, creating steam to drive a second turbine.
What are the environmental impacts?
Burning oil for electricity pollutes the air, water and land but some of the worst environmental woes associated with oil are linked to drilling, transporting and refining.
Burning oil to generate electricity produces significant air pollution in the forms of nitrogen oxides, and, depending on the sulfur content of the oil, sulfur dioxide and particulates. Carbon dioxide and methane (as well as other greenhouse gases), heavy metals such as mercury, and volatile organic compounds (which contribute to ground-level ozone) all can come out of the smoke stack of an oil-burning power plant.
The operation of oil-fired power plants also impacts water, land use and solid waste disposal. Similar to the operations of other conventional steam technologies, oil-fired conventional steam plants require large amounts of water for steam and cooling, and can negatively impact local water resources and aquatic habitats. Sludges and oil residues that are not consumed during combustion became a sold waste burden and contain toxic and hazardous wastes.
Drilling also produces a long list of air pollutants, toxic and hazardous materials, and emissions of hydrogen sulfide, a highly flammable and toxic gas. All of these emissions can impact the health and safety of workers and wildlife. Loss of huge stretches of wildlife habitat also occur during drilling. Refineries, too, spew pollution into the air, water and land (in the form of hazardous wastes). Oil transportation accidents can result in catastrophic damage killing thousands of fish, birds, other wildlife, plants and soil.
9. Electricity from: Solar Energy
The ultimate source of much of the world’s energy is the sun, which provides the earth with light, heat and radiation. While many technologies derive fuel from one form of solar energy or another, there are also technologies that directly transform the sun’s energy into electricity.
The sun bathes the earth in a steady, enormous flow of radiant energy that far exceeds what the world requires for electricity fuel.
Since generating electricity directly from sunlight does not deplete any of the earth’s natural resources and supplies the earth with energy continuously, solar energy is a renewable source of electricity generation. Solar energy is our earth’s primary source of renewable energy.
There are two different approaches to generate electricity from the sun: photovoltaic (PV) and solar-thermal technologies.
- Initially developed for the space program over 30 years ago, PV, like a fuel cell, relies upon chemical reactions to generate electricity. PV cells are small, square shaped semiconductors manufactured in thin film layers from silicon and other conductive materials. When sunlight strikes the PV cell, chemical reactions release electrons, generating electric current. The small current from individual PV cells, which are installed in modules, can power individual homes and businesses or can be plugged into the bulk electricity grid.
- Solar-thermal technologies are, more or less, a traditional electricity generating technology. They use the sun’s heat to create steam to drive an electric generator. Parabolic trough systems, like those operating in southern California, use reflectors to concentrate sunlight to heat oil which in turn creates steam to drive a standard turbine.
Two other solar-thermal technologies are nearing commercial status. Parabolic dish systems concentrate sunlight to heat gaseous hydrogen or helium or liquid sodium to create pressurized gas or steam to drive a turbine to generate electricity. Central receiver systems feature mirrors that reflect sunlight on to a large tower filled with fluid that when heated creates steam to drive a turbine.
What are the environmental impacts?
PV systems operate without producing air, water or solid wastes.
When constructed as grid-connected central station systems, they require significant land, which can impact existing ecosystems. Nevertheless, most PV installations come in the form of distributed systems that use little or no land since the panels are installed on buildings.
Manufacturing PV cells involves the generation of some hazardous materials. Nonetheless, appropriate handling of these small quantities of hazardous material reduces risks of exposure to humans and to the environment.
Like PV, solar-thermal technologies generate zero air emissions, though some emissions are created during the manufacture of both technologies. Water use for solar thermal plants is similar to amounts needed for a comparably sized coal or nuclear plants.
The biggest concern with solar technologies may be land use…
…since five acres of land are often needed for each megawatt of capacity. PV can eliminate the land use impacts by integrating the generators into building construction, eliminating the need for dedicating land use to PV generation.
Interstate Renewable Energy Council Site
Million Solar Roofs
Solar Energy Industries Association
American Solar Energy Society
Florida Solar Energy Center
Natural Resources Defense Council Photovoltaic Fact Sheet
North Carolina Solar Center (NCSU)
Solar Electric Power Association
Database: State Incentives for Renewable Energy
Union of Concerned Scientists: How Solar Works
International Solar Energy Society
Solar Energy Society of Canada
Surface Meteorology and Solar Energy (NASA site)
10. Electricity from: Municipal Solid Waste
Electricity can be produced by burning “municipal solid waste” (MSW) as a fuel. MSW power plants, also called waste to energy (WTE) plants, are designed to dispose of MSW and to produce electricity as a byproduct of the incinerator operation.
The term MSW describes the stream of solid waste (“trash” or “garbage”) generated by households and apartments, commercial establishments, industries and institutions. MSW consists of everyday items such as product packaging, grass clippings, furniture, clothing, bottles, food scraps, newspapers, appliances, paint and batteries. It does not include medical, commercial and industrial hazardous or radioactive wastes, which must be treated separately.
MSW is managed by a combination of disposal in landfill sites, recycling, and incineration. MSW incinerators often produce electricity in WTE plants. The US Environmental Protection Agency (EPA) recommends, “The most environmentally sound management of MSW is achieved when these approaches are implemented according to EPA’s preferred order: source reduction first, recycling and composting second, and disposal in landfills or waste combustors last.” http://www.epa.gov/epaoswer/non-hw/muncpl/index.htm
EPA estimates that in 1998 17 percent of the nation’s MSW was burned and generated electricity (e.g., 14% in Pennsylvania, 2% in New Jersey; 2% in California), 55% was disposed in landfills, and 28% was recovered for reuse.
In the United States, there are currently two main WTE facility designs:
- Mass Burn is the most common waste-to-energy technology, in which MSW is combusted directly in much the same way as fossil fuels are used in other direct combustion technologies. Burning MSW converts water to steam to drive a turbine connected to an electricity generator.
- Refuse-derived fuel (RDF) facilities process the MSW prior to direct combustion. The level of pre-combustion processing varies among facilities, but generally involves shredding of the MSW and removal of metals and other bulky items. The shredded MSW is then used as fuel in the same manner as at mass burn plants.
The Power Scorecard does not consider MSW a renewable energy source, because the waste stream includes materials made from fossil resources; the sources of the plant material based content (e.g., paper and wood) are unpredictable; and the waste stream would be greatly reduced with environmentally preferable waste reduction and management practices. The EPA and the federal government and some state governments classify MSW as a renewable energy source because MSW is abundant and contains significant amounts of biomass.
What are the environmental issues?
Burning MSW can generate energy while reducing the volume of waste by up to 90 percent, an environmental benefit. Ash disposal and the air polluting emissions from plant combustion operations are the primary environmental impact control issues.
MSW contains a diverse mix of waste materials, some benign and some very toxic. Effective environmental management of MSW plants aims to exclude toxics from the MSW-fuel and to control air pollution emissions from the WTE plants.
Toxic materials include trace metals such as lead, cadmium and mercury, and trace organics, such as dioxins and furans. Such toxics pose an environmental problem if they are released into the air with plant emissions or if they are dispersed in the soil and allowed to migrate into ground water supplies and work their way into the food chain. The control of such toxics and air pollution are key features of environmental regulations governing MSW fueled electric generation.
In 1995, the EPA significantly tightened the regulation of plants using MSW to produce energy. EPA then issued a new “Maximum Achievable Control Technology” rule pursuant to the Federal Clean Air Act for the waste-to-energy industry for large MSW incinerators and WTE plants. Facilities were required to comply with the new rule by the end of 2000. Small municipal waste burners are addressed in a separate similar rulemaking, put into effect in 2000. The rule requires “maximum available pollution control technology” (including bag house particulate controls, carbon injection systems and acid control scrubbers), continuous monitoring of combustion efficiency and periodic stack testing for hazardous air emissions on all incinerator/WTE facilities. The EPA studies estimate that enforcement of this new rule will reduce emissions of mercury and dioxin from WTE plants by about 90% and 99%, respectively, from their 1990 levels. However, because trash is inherently an inefficient source of fuel, WTE plant’s mercury emissions compare with coal plants on the basis of each kilowatt-hour-generated by a facility.
Burning MSW in WTE plants produces comparatively high carbon dioxide emissions, a contributor to global climate change. The net climate change impact of these emissions is lessened because a major component of trash is wood, paper and food wastes that would decompose if not burned. If left to decompose in a solid waste landfill, the material produces methane — a potent greenhouse gas.
These plants produce comparatively high rates of nitrogen oxide emissions. The on-site land use impacts are generally equal to those of coal or oil fueled plants.
US Environmental Protection Agency. Environmental Fact Sheet: Municipal Solid Waste Generation, Recycling and Disposal in the United States: Facts and Figures for 1998. EPA530-F00-024. April 2000
US Environmental Protection Agency. Greenhouse Gas Emissions from Management of Selected Materials in Municipal Solid Waste. EPA530-R-98-013. September 1998.
US EPA Municipal Solid Waste
U.S. Environmental Protection Agency, Office of Solid Waste
U.S. Environmental Protection Agency: “Greenhouse Gas Emissions from Management of Selected Materials in Municipal Solid Waste”
Integrated Waste Services Association – provides information from the waste to energy industry
11. Electricity from: Wind
Wind power is the world’s fastest growing electricity generation technology. Wind is a renewable resource because it is inexhaustible. It is a result of the sun shining unevenly on the earth. The corresponding daily and seasonal changes in temperature consistently generate wind, producing a fuel source that can never be depleted.
State-of-the-art wind power plants use large spinning blades to capture the kinetic energy in moving wind, which then is transferred to rotors that produce electricity. At the best wind fuel sites, wind plants today are nearly competitive with the conventional natural gas-fired combined-cycle plants — even when natural gas prices have recently been at historically low levels. Regions where average wind speeds exceed 12 miles per hour are currently the best wind power plant sites.
Current costs of wind-generated electricity at prime sites approach the costs of a new coal-fired power plant. Wind power is the lowest-cost renewable energy technology available on the market today. According to the Department of Energy, the costs of wind power are projected to continue to fall and may rank the cheapest electricity source of all options by 2020.
What are the environmental impacts?
Wind plants produce no air pollution. They use no water, and there is no need to tear up the land to extract the wind resource that produces wind power. Nonetheless, there may be environmental problems associated with some wind plants.
Wind power generates three categories of environmental impacts: visual impacts; noise pollution; wildlife impacts. These impacts can vary immensely from site to site.
- Because wind farms are comprised of large numbers of turbines each mounted atop tall towers in rural areas, they can often be seen for a long distance. Whether this visual impact is good or bad will vary from location to location. Some find wind turbines to be enduring symbols of self-sufficiency. Others see them as stark intrusions in the “natural” landscape.
- Wind turbines, particularly older designs, emit noise that can be heard in the vicinity of the wind farms. The level of noise produced by one wind turbine is equivalent to that of your washing machine. The frequency and volume of this noise can be controlled but not eliminated by wind turbine design.
The most controversial significant negative environmental impact of early wind turbines is the impact on bird populations, an issue largely resolved by new turbine designs.
- In the early 1980s, three major wind farms were built in passes in California. At the Altamont Pass site, deaths of birds, particularly raptors, prompted a number of studies that subsequently influenced both the design of newer wind turbines and the siting of wind farms. It was discovered that raptors perch atop the wind generators for a better view while hunting, and upon rare occasion get caught in the spinning blades when the wind begins to blow. Current wind turbine technology offers solid tubular towers to prevent birds from perching on them. Turbine blades also rotate more slowly than those of earlier designs, reducing potential for collisions with birds.
If wind power plants are sited in regions screened for sensitive local bird populations, the environmental footprint of wind-generated electricity is quite small when compared to the wildlife and ecosystem impacts of fossil fuel mining and fuel combustion.
The manufacture of wind generation technology creates some air emissions.
American Wind Energy Association
National Wind Coordinating Committee
National Renewable Energy Laboratory: National Wind Technology Center
CA Energy Commission / Wind
Danish Windpower Manufacturers
European Wind Energy Association
Union of Concerned Scientists: How Wind Energy Works
Natural Resources Defense Council Wind Fact Sheet
Minnesotans for an Energy Efficient Economy: Wind Site
Wind Energy for Electric Power: A REPP Issue Brief. Renewable Energy Policy Project. November 2003.
Also see environmental issues for more details on how electricity production affects our planet.