Environmental Benefits and Impacts
We use energy for fuel, electricity, heating, cooling, and mechanical power. The human production and use of energy has always had an impact on the environment. This impact is growing dramatically as the population increases and the demand for energy increases.
The choices we make regarding where our energy comes from and how it is used impact the environment. In order to fully understand this, we need to look at the entire life cycle of energy production and use. The processes involved include:
Manufacturing the energy conversion technologies.
Extracting, harvesting, or otherwise obtaining the energy feedstock (e.g., coal, natural gas, oil, nuclear fuel, wood or other biomass, flowing water, geothermally heated liquids, sunlight, or wind), as well as transporting and managing it.
Converting the feedstock to electricity, heat, mechanical power, or fuel.
Storing the electricity, heat, or fuel.
Transporting the electricity or fuel from where it is produced to where it is needed.
Using the energy efficiently.
Managing any waste products — including contamination of air, soil, and water.
When looking at the environmental impacts and benefits of an energy solution, it is important to look at all parts of the energy life cycle, as well as long-term management and conservation of natural resources. All approaches have environmental impacts, but we can minimize them by understanding the impacts and making wise choices.
The following are brief discussions of the environmental benefits and impacts of some key technologies. It is important to note that they represent current technology. The challenges and problems of each are being worked on through research and development. See below for information about:
- Fossil fuels
- Nuclear energy
- Renewable energy technologies
In terms of the life cycle described above, the use of fossil fuels contributes to many of the environmental problems we face today.
There are impacts to the environment from extracting fossil fuels. For example, exploration, mining or drilling may occur on sensitive lands such as tropical rain forests, arctic tundra, coastal marshes, or sacred sites. Fuels are often transported long distances at substantial cost, environmental impact, and security risk. The processes used to convert them to electricity or fuels generate large amounts of waste heat, often require water for cooling, and usually generate some combination of solid, liquid and airborne pollutants.
These pollutants include greenhouse gases and other gaseous pollutants, particulates, and water and soil contamination. Greenhouse gases (carbon dioxide, methane, nitrous oxides, hydrocarbons, and chlorofluorocarbons) surround the Earth's atmosphere like a clear thermal blanket, allowing the sun's warming rays in and trapping the heat close to the Earth's surface. The natural greenhouse effect keeps the Earth's average surface temperature at about 60ºF (33ºC). But increased use of fossil fuels has increased greenhouse gas emissions, creating an enhanced greenhouse effect known as global warming. The long-term effects associated with global warming may be devastating. Deaths due to extreme weather could increase; diseases could have a greater potential to thrive; rainfall patterns will change, causing huge agricultural disruptions; and sea levels will rise as temperatures rise.
Other pollutants that are generated by using fossil fuels include carbon monoxide, sulfur dioxide, nitrogen dioxide, particulate matter, and a variety of heavy metals. These pollutants have major impacts such as smog, acid rain, and regional haze, as well as human health impacts such as increase in asthma, lung cancer, and respiratory tract infections.
Finally, fossil fuels are finite. While the global coal resources are very large, oil and gas reserves are far more constrained. And it is increasingly clear that the atmospheric loading of carbon dioxide from combustion of fossil fuels is not sustainable at present, much less at increased rates.
Nuclear power plants require the mining, processing, transport, and disposal of nuclear materials. The processes used to generate electricity are relatively clean, and produce little air pollution, however large amounts of water are still used for cooling. Concerns regarding the environmental impacts of nuclear energy generally center on the transport and storage of nuclear waste, as well as on the potential for accidents. As a result, siting new nuclear plants has become a contentious issue, and there has not been a new nuclear plant ordered in the United States for over 20 years.
Renewable Energy Technologies
In general, renewable energy technologies are much friendlier to the environment. Renewable technologies minimize the need for mining, drilling, extraction, processing, transport, and disposal in specially prepared long term waste depositories. They produce little or no emissions, and they are sustainable, that is, the resource is not depleted through its use.
Most locations on earth have abundant renewable energy resources, though the dominant form varies significantly from one place to another. Much of the impact of transportation can be eliminated if the electricity or fuel is produced and used close to the energy source, as is often the case with renewable energy resources. (Energy that is produced close to where the energy it is used is known as a "distributed energy resource.")
However, there are still issues to be considered, depending on which technology or combination of technologies you choose. Most renewable energy technologies have a dynamic, time-varying characteristic to their behavior: the sun sets every evening, the wind is not always blowing, and biomass does not grow year around. Therefore, renewable technologies are often paired with other technologies in a hybrid system — such as a wind turbine paired with a backup diesel generator, or photovoltaic arrays paired with a battery bank — so the impacts of all parts of the system must be considered. The national utility grid is the ultimate hybrid system, and as renewable generation continues to grow, new issues are emerging regarding utility system operation.
Biomass covers a broad range of technologies. This may be as simple as burning wood or dung for cooking or heating, or as complex as industrial-scale plants that use forest products, agricultural products, or municipal waste to generate electricity or to convert into fuels such as ethanol. For more information, see Energy Technology Basics.
Worldwide, there are health concerns related to the indoor air pollution related to burning biomass for cooking or heating. These have been documented to cause increases in the rates of respiratory problems.
If the raw materials (feedstocks) used for biomass energy are not properly managed, there can be environmental problems such as deforestation. For this reason, it is important that forest or agricultural wastes are used, or that specialized energy crops are developed and managed for that purpose. There is also concern that there will be competition for biomass resources — for example, that corn and corn products will be used to generate fuels when they are needed for human or animal food.
Siting of biomass plants has several environmental considerations. First, it is most efficient to have the plant close to the feedstock — located near where forest or agricultural wastes are collected — in order to minimize the impacts of transporting the feedstock to the plant. Second, these plants may be large and industrial enough to have visual impacts. Third, depending on the technology, there may be some air pollution issues. This is especially true if a hybrid system is used, such as a combined biomass/coal power plant.
However, full life-cycle analyses show clearly that if we are responsible about replacing the plants we use as feedstock, biomass production of power and fuels are sustainable: the amount of carbon taken out of the atmosphere by growing the plants balances the carbon put back into the air in using them.
Today, geothermal plants are generally large-scale plants that take advantage of water or steam heated by the Earth to turn turbines and generate electricity. Worldwide, geothermal resources are also used for heating purposes near the site. For more information, see Energy Technology Basics.
Most modern geothermal power plants incorporate a closed cycle where the water or brine extracted from the ground is re-injected back into the ground after the heat has been extracted. The exception is dry steam plants, which exhaust spent steam into the atmosphere, requiring a source of water to replenish the steam. But since dry steam is an exceedingly rare resource, this is not likely to be an issue at new geothermal power plants.
Geothermal power plants are also located at the source of the energy, so there are no transportation impacts. Most environmental considerations are related to where they are sited: the impact of roads and drilling to develop the site; the visual impact of large, industrial plants; and the availability of water for cooling. However, research is underway to minimize the cooling-water requirements at geothermal plants, and some plants in arid climates are air-cooled.
Although geothermal plants typically emit very low concentrations of air pollutants during normal operations, component failures can cause significant concentrations of pollutants, such as hydrogen sulfide, to be emitted for brief periods of time. This may be of concern in sensitive habitats such as tropical jungles.
Some geothermal fluids also have high concentrations of impurities in them, often requiring an extra step to remove those impurities from the fluid. In such cases, the impurities may result in a solid waste stream from the plant. If these solid wastes have significant heavy metal content, they may be classified as hazardous waste.
Hydrogen may be burned as a fuel in an internal combustion engine or used in fuel cells to produce electricity. This process is clean, and the only byproduct is water.
Environmental considerations with hydrogen stem from how it is produced, how it is transported, and how it is stored. Today, hydrogen is predominantly produced by the steam reforming of natural gas. This is not an efficient process, and natural gas is not a renewable resource. In the future, hydrogen may be produced from coal plants, nuclear plants, or by using renewable approaches such as wind or solar energy. In each case, the impact of hydrogen production is the impact associated with the technology used to produce it.
There are safety concerns regarding the storage and transmission of hydrogen. It is flammable (though not more so than current fuels), and is generally compressed for storage or trucking. Current large-scale pipelines are designed for oil or natural gas rather than hydrogen, so new pipelines would have to be built or older ones converted. But, as these challenges are worked out, hydrogen may prove an excellent and clean means of storing and moving energy from one region to another.
Flowing water creates energy that can be captured and turned into electricity by channeling the flow through a turbine. Hydroelectric systems range from small scale projects that take advantage of a small stream or part of a stream, to very large systems of dams. For more information on hydropower technologies, see Energy Technology Basics.
Hydropower systems are clean, causing no emissions as they operate. Environmental concerns center around disruption to the river flow, its natural surroundings, and especially to the fish living in the river and the animals and people that rely on the natural river habitats. The impact depends on the degree of disruption of these habitats, so a small hydropower plant using only a channeled portion of the stream is less damaging than a large dam. The construction of large hydroelectric dams has had significant local impacts where whole towns have been relocated to make room for the lake, and the flooding of forests to produce reservoirs is a potential source of methane — a powerful greenhouse gas — as the submerged forests decompose. And of course, depending on siting and design, long water-diversion tunnels or aqueducts, transmission lines, and access roads can be disruptive.
Solar technologies directly convert the sunlight falling on the earth's surface to usable energy. The most common means of doing this are 1) photovoltaics (solar cells), that convert sunlight to electricity, 2) solar hot water, 3) solar heating, lighting, and cooling of buildings, 4) using solar energy for agricultural or industrial purposes such as crop drying, 5) concentrating solar power, whereby mirrors or troughs are used to superheat liquids that are then used for other purposes. For more information on solar technologies, see Energy Technology Basics.
None of these technologies require the transportation of fuels. They have no emissions and produce no waste as a byproduct of their use. As a result, their environmental impacts are limited to siting issues, particularly, issues relating to their visual impact and any impact from land use. Roof-mounted solar energy systems can often avoid both of these impacts.
Hazardous chemicals are used in the manufacture of solar cells, creating environmental considerations in their manufacture and, in some cases, in their eventual disposal. Solar cell manufacturers minimize their use of these chemicals, recycle them when possible, and release a minimum of pollutants to the environment.
Some solar cells include minute amounts of heavy metals, such as cadmium. These materials are encapsulated in the solar modules and do not present any environmental threat during their use, but could have an adverse environmental impact when the solar panels are decommissioned (although the encapsulation will also minimize these concerns). To address these issues, the photovoltaic industry is examining the processes that would need to be in place to recycle cadmium-telluride solar modules when they reach the end of their useful life.
Finally, if a battery bank is used to store the solar energy, battery disposal may be an issue, although most battery types can be recycled.
Wind machines range from small single-purpose systems (such as those traditionally used for water pumping) to utility-scale machines using large turbines on very tall towers. For more information on wind technologies, see Wind Turbines.
The use of wind turbines to produce electricity creates no pollution. Environmental concerns center primarily on visual impacts, noise, and avian issues. Some people consider wind machines visually offensive, and some people consider the noise irritating. Mitigating this is the fact the people don't normally like to live in very windy areas. Perhaps the greatest environmental concern with wind turbines is the danger of killing birds. It is important not to locate wind machines on major migratory paths, especially those of endangered species. For more information on avian issues, please see the National Wind Technology Center's Wind–Wildlife Literature Database (WILD).
A new related concern for wind turbines is that they can also impact bat populations, particularly migrating bats. A 2003 study in Minnesota by the Electric Power Research Institute found that the impact was small relative to the large number of migrating bats, but more recent studies in West Virginia have raised new concerns. As a result, the Bats and Wind Energy Cooperative was formed in 2003 by Bat Conservation International, the U.S. Fish and Wildlife Service, the American Wind Energy Association (AWEA), and the U.S. Department of Energy's National Renewable Energy Laboratory. The cooperative coordinates research on the interaction of wind turbines and bats and posts findings on their Web site.
Wind energy projects near U.S. military installations have faced special challenges, especially for projects located near sites where flight training operations are carried out. Some wind projects have been modified or cancelled because of concerns that the turbines could interfere with jet flight paths or with military radar systems. If your project is located near a military installation, it may be beneficial to begin a dialogue with the officials at that installation early in the planning process. A recent study of wind turbine interactions with radar systems, funded by the United Kingdom government, can provide valuable information for this dialogue. The study, Feasibility of Mitigating the Effects of Wind Farms on Primary Radar, determined the key factors influencing the interaction of wind turbines and radar systems, and can be used to modify a wind power plant proposal to meet the military's needs.
See the AWEA Web site for a helpful overview of the interactions between wind energy and the environment.
The National Wind Coordinating Collaborative has published a document that discusses various methods of avoiding, minimizing, or compensating for the impacts on wildlife caused by wind power facilities. See the NWCC's Mitigation Toolbox (PDF 1.3 MB). Download Adobe Reader.