Choosing Green Energy: A Consumer's Guide to Sustainable Electricity
The production of electricity causes more damage to the environment than any other single human activity. Electricity production is now the largest single use of energy in the United States. Electricity generation is responsible for 69 percent of the sulfur dioxide and 32 percent of the nitrogen oxide emissions that foul the air and cause acid rain. Electricity use accounts for 35 percent of U.S. carbon dioxide emissions, the key culprit in global climate change. It is responsible for millions of miles of rivers and streams being disrupted by dams, hundreds of tons of nuclear waste that must find a permanent home somewhere, and thousands of tons of air pollutants that are a major cause of respiratory problems.
With the deregulation of the electricity industry and the startup of "green electricity" suppliers, many consumers can now vote with their dollars for a more sustainable electricity industry and a more sustainable future. But to make an informed decision, you need to know about the different sources of electricity available and how each one affects a range of environmental issues. This consumer's guide puts the power to decide in your hands.
This section provides key background material on the electricity industry.
These sections review the different sources of electricity, identify criteria sources must meet to be sustainable, and examine how well each source meets the criteria.
This section rates each source on its overall sustainability.
Armed with this information, you can examine the power sources of your local utility to see how sustainable your electricty is - or even better, if your state allows you to choose your electricity supplier, to compare utilities to decide which is "greenest." Your decision is important. Although we have yet to find the perfect source of electricity - one that is truly sustainable by all criteria -- we can not afford to delay converting to sources that are at least more sustainable. The consequences of our current path are too dire.
Today's world is unimaginable without electricity. Electricity powers everything from coffee makers to computers. Between 1949 and 1998 the U.S. population grew by 82 percent, but the amount of electricity sold by utilities grew by 1,200 percent, and today electricity use per person is six times higher than it was 50 years ago.
At the point of use, electricity is a clean, flexible, controllable, safe, effortless and instantly available form of energy. Electricity is a common energy currency: Your power company could be using any number of different fuels to generate electricity, but your refrigerator knows no difference. As our appetite for electricity grows, it is essential that we shift to more sustainable sources of electricity: those that do not threaten the ecological, social and economic well-being of present and future generations. Over the next 50 years virtually all of the equipment used to produce and consume energy will be replaced, and consumers now have a remarkable opportunity to influence the future of electricity.
Until very recently, consumers had no choice in what company would provide their electricity. But this is changing rapidly. Deregulation of the electricity industry is occurring in, or being considered by the legislature of every state in the nation. Customers in California and Pennsylvania already can choose their electricity provider, and as they are learning, significant differences do exist between suppliers. Some companies boast of their use of renewable resources such as wind, solar and small hydro. Even among conventional energy suppliers there are important variations, some relying mainly on nuclear power and others on coal or natural gas. For the consumer, this choice brings both responsibility and opportunity.
If consumers choose haphazardly they are turning a blind eye to the significant environmental impacts associated with electricity generation. But if consumers consistently choose companies that provide sustainable energy and encourage their local governments, employers, churches, and businesses to do the same, the power of the marketplace will encourage a transition to a sustainable energy future. More importantly, by choosing a sustainable supply of electricity sources, citizens can send a powerful message to politicians and utility companies that sustainability is important. The effects would not just be seen in the United States. As a the world's major industrial power, cultural influence and source of pollution, America's shift to sustainable electricity production would have profound effects on the global environment.
The kinetic energy of the wind can be harnessed with turbines that, although they are quieter, sturdier, and more efficient, are not far from the age-old windmill. Once installed, turbines produce no air or water pollution beyond a negligible amount produced during occasional maintenance. Although wind energy can only be generated in windy areas, the potential for wind energy in the United States is tremendous. It is estimated that the wind energy potential in just two states, North and South Dakota, could meet 80 percent of the nation's electricity needs. A potential drawback to wind power is that it relies on a naturally variable resource that, though renewable, can not be turned on and off according to demand. But the fact that the wind is likely to be blowing somewhere has underlied findings that up to half of overall system energy could be derived from wind power before running into problems associated with variability. Wind power now contributes less than 1 percent of the electricity used in the US, but it is also the least expensive and fastest growing renewable energy source.
The solar energy falling on the Earth each day equals nearly 500,000 times the electric power capacity of the United States. This energy can be converted directly to electricity by photovoltaic cells (PVs) which produce an electric current when struck by sunlight. Because the solar energy supply is inexhaustible, its potential for electricity generation is limited only by the efficiency at which we can capture it and the amount of surface area we can devote to it. PVs are typically 99 percent silicon, an inert substance which is the second most abundant element on Earth and a primary constituent of sand. PVs work without sound, air or water emissions, moving parts, and require little maintenance and no water. Even when you consider the manufacture of photovoltaics the environmental impacts are very low, and the PVs themselves are recyclable after their useful life ends. Currently solar power contributes less than 1 percent of our electricity. Expansion has primarily been hampered by its high cost, although this has fallen significantly in the last decade. Another drawback to PVs is that they only generate electricity when the sun is shining. At a small scale, therefore, some sort of energy storage or back-up system is required. At larger scales, however, studies and field experience have shown that integrating intermittent PV-generated electricity into the electric grid provides few technical difficulties, even when considering much higher levels of solar power usage.
Biomass refers to wood, crops, harvest residues, urban refuse, or methane gas produced by landfills that are burned to spin turbines and produce electricity. Biomas is an attractive energy source because it avoids two drawbacks accompanying most other forms of renewable energy: high cost of collection and intermittency. The solar collectors are the leaves of plants, requiring much less capital than wind turbines or PV cells and providing a convenient medium for energy storage, allowing electricity to produced on-demand, and contributing no net carbon dioxide to the atmosphere. However, if biomass were used for electricity production on a large scale, the impacts would be significant. For example, commercial applications of biomass would require vast acreage of fertile land to be committed to trees or crops grown specifically for energy production. Furthermore, biomass-fueled electricity production would also be extremely water intensive. Put in perspective, to produce electricity for just one household over the course of a year with biomass as a source would require over 25,000 gallons of water and almost three quarters of an acre of land. It also produces 232 pounds of carbon monoxide per household each year -- more than thirty times the level of any other source, as well as significant amounts of other air pollutants. Combustion of wood now contributes about 1 percent of the nation=B9s electricity supply, and the electricity generated from waste about half that amount. Waste is not considered a viable option for large-scale electricity production and is not a truly renewable resource.
The kinetic energy of flowing water can also be used to spin turbines. Hydroelectricity, which currerntly generates about 9 percent of the nation's electricity, is renewable, can produce electricity on-demand, and generates electricity with few emissions. On the other hand, a dam can have devastating impacts on the ecological systems up and downstream. In the United States alone there are more than 5,500 large dams impeding our rivers, leaving less than 2 percent of our country's 3.1 million miles of rivers and streams flowing free. An important distinction to make, however, is between large and small hydroelectric projects. Large hydro projects involve constructing a large dam on a river and flooding its river basin to create a reservoir. Small hydroelectric plants generate less than 30 megawatts of electricity and have much smaller impacts than large hydro projects, though they may not always be able to provide on-demand power because they are much more susceptible to variations in river flow. Because the most promising large dam sites in the United States have either been developed or protected, and because the general public has become outspoken about the negative impacts of large dams, dam construction has been declining.
Natural gas was formed millions of years ago when buried organic matter was subjected to very high temperatures and pressures. Although the formation process continues, the rate is negligible compared to the rate of human extraction, making natural gas a non-renewable resource. Natural gas may be found along with coal or oil, or it may be found alone; off-shore drilling is becoming more prevalent, with about one-fifth of U.S. natural gas coming from off-shore sites. Once extracted and refined, the gas is burned to create steam, which then turns turbines to produce electricity. About 15 percent of US electricity comes from natural gas combustion. Like coal, natural gas is relatively cheap, the technology involved is simple and widespread, and electricity can be produced on-demand. It produces much lower levels of air pollutants such as particulates, sulfur dioxide and nitrogen oxides than coal, but significantly more than other source apart from biomass. For instance, a household supplied only by natural gas for a year would generate 24 pounds of air-borne particulate matter which has been implicated in respiratory infection and asthma. Maybe most significant, however, is the amount of the greenhouse gas carbon dioxide emitted during natural gas combustion: over 10,000 pounds per household per year if natural gas were the sole source. Touted as the cleaner alternative to coal, this claim may be true, but it doesn't make natural gas sustainable.
Coal production has been increasing since the 1950s, and today the United States extracts huge quantities of coal (over 1 billion short tons in 1998). Currently, coal contributes over half of the nation=B9s electricity, and over 90 percent of the coal produced is used for electricity generation. Besides being cheap and abundant, the only thing that coal has to recommend it is that is can provide power on-demand. Coal mining has major impacts on terrestrial and aquatic ecosystems. In many cases, whole mountaintops are removed for coal extraction, and valleys are filled in with the waste rock (tailings). Whether it is mountain-top removal, open-pit, or underground mining, however, a major problems stems from rain filtering through the coal mine and tailings. Some of the sulfur in the coal dissolves into the water, turning it acidic; this "acid mine drainage" has impacted thousands of stream miles across the country. The combustion of coal also produces many gaseous wastes, some of which are "scrubbed" out of the emission stream in smokestacks, but many are not, including carbon dioxide. A single household being supplied solely from coal-produced electricity would generate over 61 pounds of sulfur dioxide, 60 pounds of nitrogen oxide, 30 pounds of particulates, 6 pounds of carbon monoxide, 2 pounds of volatile organics, and 17,000 pounds of carbon dioxide, and require over 7,000 gallons of water.
While every other source of electricity is basically solar energy in one form or another, nuclear power harnesses the power contained within the nuclei of atoms. Consequently, risks and impacts involved are unique. With its low emissions and low land use, nuclear seems falsely attractive at first glance, but when you begin to look at its entire lifecycle, the potentially devastating human health and safety concerns are clear. The nuclear fuel cycle begins with the mining of uranium ore (a non-renewable resource), releasing radon (radioactive gas) and creating large amounts of radioactive waste rock (tailings). The uranium is then processed in a highly energy-intensive process and fabricated into fuel rods. Nuclear power plants produce energy through either fission reactions (when an atom of a radioactive element such as uranium or plutonium collides with a neutron, splitting the element apart) or fusion reactions (where two elements collide at high speed, forming one or more heavier elements). In both cases, a large amount of heat is released which is used to create steam to turn turbines and generate electrical energy.
Along with heat, a significant amount of radiation is produced. Radiation is extremely dangerous to people and biological systems, causing acute illness or death at high doses, or cancer or genetic mutations at lower doses. Although most of this radiation is not released into the atmosphere, it does not disappear. It is contained instead in large amounts of radioactive waste, which remains hazardous for many thousands of years. No permanent facility for the storage of high-level waste exists, and even if one is built, it may adequately contain the waste for only 1,000 years. Routine plant operation produces upwards of 3.64 tons of low-level waste per GWh of electricity, and about 30 to 40 tons of high-level waste over the course of a power plant year. The largest volumes of nuclear waste, however, stem from the decommissioning of plants at the end of their life spans. Current decommissioning practices of reactors consist of processing some of the waste, but "mothballing" the reactor core and much of the rest of the reactor in the hopes that better methods of dealing with its might be found in the future.
One of the most frightening propositions in the modern world is the event of an accident involving a nuclear power plant or radioactive waste. The U.S. Nuclear Regulatory Commission (NRC) has estimated that there is a 45 percent chance of a severe accident occurring in the next twenty years at one of the 109 U.S. reactors. The possibility of an accident and the unavoidable reality of the nuclear waste highlights a moral issue: what are we leaving for our children and all future generations? The risks that stem from the air pollution emitted during fossil fuel combustion are significant, but they have short-term impacts only. The same people (or at least generation of people) that are suffering the costs are also receiving the benefits of that electricity. In contrast, the legacy of the nuclear electricity being produced and consumed today will continue to pose a threat for many generations to come.
Nuclear power plants multiplied rapidly during the late sixties and early seventies, but interest declined for various reasons including high operating costs, and public disfavor over the risk of serious accidents after the Three Mile Island incident in 1979. Currently, nuclear provides the United State with a little less than 20 percent of its electricity. More than half of the current reactors are scheduled to retired in the next 20 years and no new ones are scheduled to be built. Consumers can send a loud message to the electricity industry by refusing to buy power that includes nuclear in the mix.
Table 1. Pros and Cons of Electricity Sources
Sustainability implies long-term social, economic, and ecological health and vitality. How can we make sense out of all these disparate yet interrelated issues? The price paid per kWh of electricity poorly reflects the true cost of a particular electricity source and obscures the unique profile of advantages and drawbacks for each electricity source. Moreover, weighing the impacts of, say, coal combustion on human health vs. the impacts of a large hydroelectric dam on the health of a river ecosystem is like comparing apples and oranges. A truly sustainable electricity source must be renewable, reliable and economical, with minimal impacts that would affect the well-being of present or future generations of people or ecosystems. More specifically, a source must meet the criteria listed below.
To see how the different sources stack up on each issue, click on the name of the issue.
To see how the different sources stack up overall, click on The Bottom Line.
To look at detailed tables of quantitative data comparing the sources, click on Appendix.
- Must be renewable over the long term
- Land required for electricity production must be small
- Degree of impact and risks to terrestrial habitat must be low
- Areas of high value for food production, wildlife habitat or aesthetic value must not be required
- Amount of water required for electricity production must be small
- Degree of water pollution and damage to aquatic habitat must be low
- Must not endanger drinking water supplies.
- Amount of air pollutants generated over entire lifecycle must be small
- Emissions of air pollutants most dangerous to human health must be particularly low
- Emissions of greenhouse gases must be low
- Occupational risks must be low
- Risks to public during general operation and in case on an accident must be low
- Risks to the health and well-being of future generations must be low
- Return-on-investment ratio must be high
- Ratio must reflect the entire lifecycle
- If likely to change, the ratio must be more likely to increase than decrease in the future
- Price must be low enough to be economically feasible
- Price must not be out of line with the true costs to society
- Price should be more likely to drop in the future than rise
|Source||How well does it meet the criteria?||Rating|
|Wind||Wind energy is a form of solar energy. Winds are caused by temperature differences among the land, sea and air, and by the overall temperature gradient that exists from the equator to the poles. Wind will be available as a source of electricity until the sun stops shining.||10|
|Solar||The sun gives life to our planet, driving the water cycle and the winds, providing energy for plants and, in turn, virtually all other organisms. The solar energy supply is inexhaustible. Its potential for electricity generation is limited only by the efficiency at which we can capture it and the amount of land or surface area that we can dedicate to this purpose.||10|
|Biomass||Biomass production relies on solar energy. However, to be truly renewable, biomass production must employ sustainable farming methods that do not erode soil sources or productivity. Most biomass being produced today does not employ such methods, and its renewability score reflects this.||8|
|Small Hydro||Hydropower is another indirect form of solar power: the sun drives the planetary water cycle. The renewability of small hydro depends on the longevity of the dam involved. Although silt flowing downstream will eventually fill up the reservoir, it can be removed from a small hydroelectric system with some effort. Run-of-the river type systems, which basically put turbines in the flow of the river, have no such problems.||9|
|Large Hydro||Although flowing water is a renewable resource, there has been some debate over whether large-scale dams truly generaterenewable electricity. Over time, the constructed reservoirs will eventually silt-in (the silt being highly expensive and difficult to remove), and dams will eventually fail. The time scale involved, however, is relatively long and depends on the silt road of the river being dammed.||7|
|Natural Gas||Although natural gas is continually being formed, humans are extracting it at a rate many tens of thousands times higher than the formation process is occurring. New reserves are found and new techniques of extraction developed. However, with escalating energy use the resource will be depleted within the next two hundred years.||1|
|Coal||Like natural gas, coal is being extracted at a rate astronomically higher than its formation rate. Coal stocks are more extensive than those of oil and gas, but are only expected to last two to four centuries at current consumption levels.||1|
|Nuclear||Although nuclear power requires a small volume of fuel relative to the power produced, huge amounts of uranium ore must be processed, and uranium is ultimately a nonrenewable resource.||1|
|Source||How well does it meet the criteria?||Rating|
|Wind||About 11,500 hectares of land are required to produce a billion kWh of electricity (enough to power a city of 100,000). However, only 233 of these hectares are actually taken up by the turbines themselves or by access roads and the rest of the land is highly compatible with other land uses such as grazing or agriculture. Although not appropriate in wilderness, in migratory pathways or areas important to threatened bird populations, the effects of well-sited wind farms on birds have been found to be much less significant than other factors.||8|
|Solar||A solar electricity plant would require about 2,000 hectares to produce a billion kWh of electricity. Although this is a significant amount of land, the amount should decline as photovoltaic (PV) efficiencies increase, and can also be offset somewhat by the use of rooftops, sides of highways and other unusable land. Furthermore, PVs do no harm to the land itself and pose few threats to wildlife populations other than the land required.||7|
|Biomass||Between 130,000 and 220,000 hectares of fertile land would be required to produce a billion kWh, depending on the type of biomass. Ignoring any other effects of biomass on terrestrial habitats, this fact makes large-scale biomass impossible.||1|
|The amount of land required to produce a billion kWh is extremely variable when it comes to hydropower. It is estimated that about 75,000 hectares on average are required. On the other hand, micro-hydro systems that use turbines in the flow of streams require basically no land at all. It also debatable whether the effects of many small scale dams would have significantly fewer effects than a single large dam.||4
|Natural Gas||Although data for the amount of land required for natural gas extraction per kWh of electricity produced are not available, it is safe to say that natural gas has the lowest land requirement of all the sources of electricity considered. However, even this may be significant if located in an important wild area such as the Arctic National Wildlife Refuge. Other terrestrial habitat effects depend on the amount of gas extracted along with coal vs. with oil or extracted alone.||8|
|Coal||Over 350 hectares of land are required for coal extraction and plant construction, but this is a low estimate since it does not include land needed for the disposal of mine tailings or ash produced during combustion. The terrestrial habitat impacts of coal production are overwhelming. Coal mining transforms the landscape on a large scale by removing mountaintops, filling in valleys, and often failing to properly clean up the mine once closed.||1|
|Nuclear||Nuclear power requires a relatively small amount of land (about 50 hectares) to produce a billion kWh of electricity. This number does not include the land needed for disposal of uranium tailings produced during mining, the waste produced during electricity generation, or the land requirements involved in the eventual decommissioning of the reactor. The land used to store high-level radioactive waste (and in a large vicinity) is basically unusable for eternity. Furthermore, nuclear power places terrestrial ecosystem health at great risk in the case of an accident.||1|
|Source||How well does it meet the criteria?||Rating|
|Wind||The amount of water consumed during construction and operation of wind turbines is tiny. If pumped hydro were used to store wind-generated energy, the water utilization would be higher. Otherwise, water usage and effects to aquatic habitats by wind power are negligible.||10|
|Solar||The small amounts of water for PV-produced energy are used for periodic washing of the panels; the water used during construction is negligible. Similarly, the effects on aquatic habitats are minimal.||10|
|Biomass||A wood-fired steam electric plant would require about 8.5 acre-feet of water per GWh of electricity produced, but this number would be much higher if energy crops were planted that needed water for irrigation (and water is a major limiting factor in agricultural production). A more significant impact, however, would come from the runoff of soil, fertilizers and pesticides typically used in industrial agriculture which is causing significant problems for stream and river habitats around the nation.||2|
|A medium-sized hydroelectric plant uses about 66,000 acre-feet of water per GWh of electricity. This water is not consumed, but the impacts are nevertheless large because all organisms must be screened out before use. The major impacts, though, stem from the effects of dams on the upstream and downstream aquatic habitats. Many miles of a river basin are flooded with the construction of a large dam, adversely affecting any fish species that need flowing water for reproduction or those (like salmon) that must swim upstream to complete their lifecycle. Water quality downstream from a dam differs substantially from the water entering a reservoir, and the hydrologic regime of the river itself is also altered, being dictated by power demand rather than by seasonal changes in precipitation which have occurred naturally for eons. As for small systems, at this point it is unclear what the effects on aquatic habitat would be if small dams were constructed on a large scale.||4
|Natural Gas||A little less than one acre-foot of water per GWh is consumed during natural gas combustion, but about 600 acre-feet are used and recycled. This latter amount is significant if it is extracted from a lake or river and then returned. It is also important to consider the pollution to the oceans that takes place during off-shore oil and natural gas production, making natural gas less sustainable in terms of aquatic habitat impacts.||7|
|Coal||Coal combustion consumes between 1.5 and 3 acre-feet of water per GWh, and uses about 600 acre-feet of non-consumptive water. Coal's aquatic habitat impacts are significant, however, because of the problems of acid mine drainage harming streams and rivers (in the case of surface mines) and poisoning groundwater (in the case of underground mines).||1|
|Nuclear||Nuclear reactions require between about 2.5 and 4 acre-feet of water per GWh, and about 800 acre-ft of non-consumptive water. Studies have shown that this amount of water can have a significant impact on nearby aquatic habitats because of the number of organisms killed when the water is screened to remove debris (one study in Delaware, for instance, found a 31 percent reduction of the bay anchovy as a result of water consumption from a single reactor. The real impacts appear when you consider the risk to aquatic habitats and drinking water from underground radioactive waste storage or in the event of an accident.||1|
|Source||How well does it meet the criteria?||Rating|
|Wind||Wind power produces only a trace of air pollution per GWh over its entire lifecycle and the amount that is produced stems mostly from fossil fuel burning from construction and maintenance. It also emits less than 8 tons of CO2 per GWh of electricity, again mostly from fossil fuel burning (so emission levels would drop even more if cleaner sources were used).||10|
|Solar||Like wind, solar power produces only a trace of air pollution per GWh over its entire lifecycle and the amount that is produced stems mostly from fossil fuel burning from construction and maintenance. Its emission levels of CO2 are even lower than wind, just 5.4 tons per GWh of electricity, again mostly from fossil fuel burning.||10|
|Biomass||Biomass combustion emits very high levels of carbon monoxide (CO), volatile organic compounds (VOCs), significant levels of particulates, and lower but not negligible levels of nitrogen dioxide (NO2) and sulfur dioxide (SO2), all of which have significant effects on human health, with the latter two also contributing to the terrestrial and aquatic habitat-sickening problems of acid rain. If biomass is grown sustainably it would not contribute any net CO2 to the atmosphere aside from the (possibly significant) amount used for the energy required for fertilizers, pesticides, planting and harvesting.||6|
|Both small and large hydro produce only a trace of air pollution per GWh over the entire lifecycle; the amount that is emitted stems mostly from fossil fuel burning from construction and maintenance. Emission levels of CO2 are also low, ranging from 3 to 10 tons per GWh of electricity, again mostly from fossil fuel burning.||10|
|Natural Gas||Natural gas produces much lower levels of SO2 and NO2 than coal, but these are still much higher than almost any other source. Natural gas also produces very high levels of particulates (though still lower than coal), which are some of the most hazardous to humans. It is the high emission levels of CO2, however, that particularly mark natural gas as unsustainable: between 500 and 600 tons of this greenhouse gas is produced per GWh of electricity.||2|
|Coal||Coal is the out and out loser when it comes to air and climate issues. A typical coal plant produces almost 3 tons each of SO2 and NO2, and over 1.5 tons of particulates for every GWh. Throw in significant levels of CO and VOCs, plus a whopping 750 to 950 tons of CO2 emitted for every GWh of electricity produced, and coal is just as dirty as its reputation.||1|
|Nuclear||Although nuclear power produces very little of the typical air pollutants we concern ourselves with, and only emits about 8 tons of CO2 per GWh, it can't be taken off the hook because of the risk it would pose in the case of an accident.||7|
|Source||How well does it meet the criteria?||Rating|
|Wind||Wind power is an all-around very safe method of producing electricity. Both during normal operation and in the case of an accident, the occupational hazards are low, as are the hazards to the public. Wind power poses no threat to future generations.||10|
|Solar||Solar power probably poses the least threat to human health and safety than any other source of electricity. The dangers posed to workers. the general public and future generations are close to zero, considering both normal operation and accident scenarios.||10|
|Biomass||Aside from the air pollution produced (which is significant), biomass poses few threats to the general public during normal operation or in the case of an accident. In contrast, however,, agriculture and forestry both have extremely high rates of occupational illness and injury, significantly exceeding even those of underground coal mining. Biomass does not pose any threats to future generations.||6|
|Hydroelectricity is an interesting case in terms of human health and safety. On one hand, hydroelectric dams pose few threats to the general public during normal operation, and in fact can provide some measure of flood control for citizens living downstream (large dams more so than small ones). On the other hand, although the probability is low, the failure of a dam would be disastrous (again, large ones more so than small ones). Hydroelectricity poses few threats to future generations, but no data in available on occupational hazard rates.||9
|Natural Gas||Natural gas has an occupational illness and injury rate that is about half that of coal mining, and threats to the general public are relatively low aside from the air pollution produced. The high amount of carbon dioxide produced during electricity production, albeit again less than coal, is contributing to global climate change which threatens the health and well-being of future generations.||5|
|Coal||With the highest levels of occupational hazards and air pollution emissions of any of the other sources of electricity, coal is a loser when it comes to human health and safety. Furthermore, coal poses a threat to future generations in terms of it carbon dioxide production affecting global climate, as well as its potential long term impacts on ground water supplies with continuing acid mine drainage.||2|
|Nuclear||Nuclear power poses significant human health and safety hazards. Although occupational hazard data make nuclear power seem like a relatively safe option, the data do not reflect the fact that radiation-linked cancers and other illnesses often take many years to appear. An accident at a nuclear power plant, of course, would also put employees and the general public in huge danger. But even under normal operation, the low and high level radioactive waste pose a significant threat to the health and safety of the nations citizens of today, as well as that of many generations to come.||1|
|Source||How well does it meet the criteria?||Rating|
|Wind||The energy return on investment ratio for wind power is calculated to be 5:1 over its entire lifecycle. This ratio is likely to increase in the future as designs improve and lighter-weight materials are incorporated||7|
|Solar||PV systems have a lifecycle 9:1 energy return ratio when their efficiencies are about 7.5%. This estimate is low, however, because more recent PV systems are achieving 10-15% efficiencies in the field, and prototype modules are reaching much higher efficiencies in the laboratory. A more likely figure for energy return on investment, therefore, may be 17:1.||8|
|Biomass||Biomass has a very low energy output to input ratio of 3:1 for natural forest biomass. Ratios for crops grown specifically for electricity production vary greatly but would probably be even lower: although yields for energy crops would be higher per acre than natural forest biomass, these gains would be offset by the greater energy inputs associated with intensive agriculture.||1|
|Hydropower has by far the most favorable energy return on investment, with a value of 48:1. However, such returns should not be expected from future dams because the most favorable sites have already been developed or set off-limits. The future ratio may be expected to be closer to 15:1 (which has been calculated for Europe), though this continues to be significantly higher than the ratio for any other source of electricity.||10|
|Natural Gas||Information on the energy investment for natural gas plants is not available. However, some natural gas is extracted along with coal, and would therefore have the same ratio. As for gas that is tapped along with oil or by itself, the ratio is likely to be somewhat lower than that of coal because the extraction is less energy intensive.||8|
|Coal||The energy return for coal has been calculated to be 8:1. This is a significant overestimate, however, because it does not take into consideration the energy required to extract the coal. Although more efficient technologies may increase the ratio in the future, these gains could be balanced by the decreased plant efficiencies that come with more stringent pollution controls.||7|
|Nuclear||The myth of nuclear power is that it has a very high energy return on investment. When you look at the amount of energy required to construct a plant compared to the amount of energy that is produced, however, the ratio is only 5:1. Furthermore, even this value is an overestimate because does not include the significant energy required for uranium mining and processing into fuel rods, the treatment of and storage of the radioactive waste produced and the eventual decommissioning of the nuclear reactor.||2|
|Source||How well does it meet the criteria?||Rating|
|Wind||Wind power has a current market price of 5 to 7 cents per kWh of electricity, which makes it competitive with other more traditional methods of electricity generation. This price would be expected to drop further if wind power became more widespread. Furthermore, the estimated externality costs (which are monetary estimates of the impacts on human health, natural ecosystems, climate, agriculture, etc.) for wind are low: in he range of 0 to 0.4 cents/kWh, meaning that the current market price is in line with the true cost of the electricity produced.||8|
|Solar||The largest drawback to solar power is price, with electricity from PV systems costing about 30 cents/kWh. Although this price has dropped considerably in the last few decades, and will continue to drop as it becomes more widespread, it is not very cost effective today. On the other hand, its externality costs are estimated to be in the range or 0 to 0.4 cents/kWh.||2|
|Biomass||The price for biomass fueled electricity is on the high side, costing between 7 and 10 cents per kWh. This price could drop in the future if more efficient techniques were developed, but any drop would not be dramatic because the technologies already been long employed. The externality costs have been estimated as being as high as 0.7 cents/kWh.||4|
|Hydropower is the least expensive form of electricity with a price of just 2 cents/kWh because most large dams have been around for decades and once one is built the operating costs are very low. Of course, if a new dam is being constructed and this cost is factored in, the price of electricity would be significantly higher. There are no available estimates of externality cost per kWh, but they would be greater than zero.||9|
|Natural Gas||Natural gas is an inexpensive source of electricity, with a price of 4 to 6 cents per kWh. The US currently imports about 15% of its natural gas (from Canada), so unlike oil, the price is not likely to be heavily affected by global politico-economic events. Over the long term, however, as domestic supplies become more scarce, this may change. The low price is also artificial: externality costs have been estimated to be as high as 2.8 cents/kWh.||7|
|Coal||Coal is a slightly cheaper source of electricity that natural gas, with a current market price of 3 to 6 cents/kWh. This price is not expected to increase in the near future due to supply issues because the US gets all of its coal domestically; the price could increase, however, as more environmental controls on coal plants are installed. Yet coal's low price is extremely out of line with its true cost: externality values have been estimated to be as high as 25.8 cents/kWh.||6|
|Nuclear||Despite the claim that nuclear power was going to be so cheap produce, that plants were going to be basically "giving electricity away," it was soon discovered that nuclear power was actually a very expensive source of electricity. Current market prices range between 5 and 21 cents per kWh; even higher are the externality costs which are estimated to be as much as 37.8 cents/kWh. Prices are expected to increase rather than decrease as the true costs of decommissioning and long-term waste storage are discovered.||1|
How do the various sources of electricity we have to choose from stack up when you look at all the issues overall? Here are EWG's ratings assessing how well each of the sources meet our criteria for sustainability on each issue. The ratings were based on a combination of quantitative and qualitative data. See Appendix and Environmental Impacts for more information on the qualitative components or our ratings.
Table 9. Rating the Sources: The Bottom Line
|Wind||Solar||Small Hydro||Large Hydro||Nat. Gas||Biomass||Coal||Nuclear|
|Air and Climate||10||10||10||10||2||6||1||7|
|Health and Safety||10||10||9||7||5||6||2||1|
|Energy Return Ratio||7||8||10||10||8||1||7||2|
Appendix: Values Used in Calculating the Ratings
Fuel Mix for Electricity Generation in the US
Table A1. Sources of electricity used for electricity generation in 1998. Table adapted from EIA, 1999 a.
|Electricity Source||Billion kWh||% of Total|
|Biomass: Wood a||33.6||0.93|
|Waste: MSW and LFG b||17.8||0.50|
|Other gas c||12.8||0.35|
|Biomass: Other waste d||3.3||0.09|
a Wood, wood waste, wood liquors, peat, railroad ties, wood sludge, and spent sulfur liquor
b Municipal solid waste and landfill gas
c Butane, methane, propane and other gases
d Agricultural waste, straw, tires, fish oils, paper pellets, tall oil, sludge waste and waste alcohol
e Photovoltaics, solar ponds, and solar thermal
Table A2. Land required each year for facilities that produce 1 billion kWh/yr of electricity (enough to supply a city of 100,000 people). Some sources of electricity (such as hydro) require a one-time land allotment and no new land is disrupted each year. Other sources (such as coal) have one-time land allotments in the construction of the power plant, but also require new land to be disrupted each year for fuel extraction. In these cases, it is noted how much land is required for facility construction vs. fuel extraction (when such information is available). Table is adapted from Pimentel et al. (1994 a); data on fuel extraction vs. plant operation land requirements is from USDOE (1989 b); natural gas data is from Ottinger et al. (1991).
|Source of electricity||Hectares per billion kWh|
|Natural gas||9 b|
|Wind||233; 11,666 e|
|Photovoltaics||1350 - 2700 f|
|Biomass||132,000 -220,000 g|
a Coal: Estimate includes coal power plant construction (33 ha) and coal fuel extraction (330 ha), but does not include land needed for disposal of coal mine tailings or ash produced during combustion.
b Natural gas: Estimate includes power plant construction only, and does not include land required for fuel extraction (which is likely to also be low).
c Nuclear: Estimate includes nuclear power plant construction (22 ha) and fuel extraction (26 ha), but does not include land needed for disposal of uranium tailings produced during mining, the waste produced during electricity generation, or the land requirements involved in the eventual decommissioning of the reactor.
d Hydroelectric: Estimate is based on a random sample of 50 large hydropower reservoirs in the US, ranging from 482 ha to 763,000 ha. The amount of land flooded depends on the particular topography of the region.
e Wind: It takes more than 11,500 ha of land to space out enough wind turbines such that they can produce a billion kWh of electricity. However, 233 of these hectares are actually taken up by the turbines themselves, or by access roads for their construction and maintenance. There is also an offshore wind farm that is being planned which would avoid terrestrial impacts altogether.
f Photovoltaics: Estimate includes land covered by a photovoltaic electricity generating facility. The 2700 ha number is based on an actual PV electricity plant with an overall 7.5% efficiency. This is somewhat an overestimate of the land required because the PV panels on the market have efficiencies of up to 15%, and those under development have efficiencies of up to 30%. A more modern PV plant, therefore, would cover about 1350 ha.
g Biomass: Estimate is based on the amount of natural forest that would have to be permanently set aside for sustainable forestry. If energy crops were grown, the amount of land required would drop to the still very high number of 132,000 ha.
Table A3. Water consumption for fuel extraction, and the construction and operation of electricity-generating facilities in terms of acre-feet of water used per GWh of power produced. Data includes consumptive water use only (most of which is lost as evaporation from cooling systems) and does not include non-consumptive water use (which returned to the water body from which it was drawn), unless otherwise indicated.
|Source of electricity||Acre-ft water per GWh|
|Coal||1.5 - 3.1 a|
|Natural gas||0.8 b|
|Nuclear||2.6 - 4.1 c|
a Coal: The amount of water depends on the technology and type of coal used (USDOE, 1989 a). Non-consumptive water use for fossil fuel plants is much higher, averaging 590 acre-ft per GWh (Ottinger et al., 1991).
b Natural gas: The value of 0.8 acre-ft/GWh includes consumptive water use only (USDOE, 1983). Non-consumptive water use for fossil fuel plants is much higher, averaging 590 acre-ft per GWh (Ottinger et al., 1991).
c Nuclear: Nuclear reactions generate large amounts of heat, and therefore require large amounts of water for cooling purposes (USDOE, 1989 a). Non-consumptive water use for nuclear plants is much higher, averaging 806 acre-ft per GWh (Ottinger et al., 1991).
d Hydroelectric: The 66,000 acre-ft of water is calculated for small hydro plants (in this case, assumed to be less than 65 feet) and is non-consumptive (USDOE, 1983). Even though the water is not consumed, because all organisms must be screened out before use, the impacts of this water use are large.
e Wind: The water consumed during construction and operation of wind turbines is negligible (USDOE, 1983). However, if pumped hydro were used to store wind-generated energy, the water utilization would be much higher.
f Photovoltaics: The small amounts of water for PV-produced energy are used for periodic washing of the panels; the water used during construction is negligible (USDOE, 1989; Ottinger et al., 1991).
g Biomass: This water is used in a wood-fired steam electric plant (USDOE, 1983). Energy crops that require irrigation would consume much higher levels of water.
Air Pollution Emissions
Table A4. Emissions of 5 major air pollutants from electric power generation over the fuel lifecycle. Tr stands for trace (less than 0.01 tons/GWh). Adapted from USDOE, 1989 a. Externality values are from EIA, 1995.
|Tons of pollutants per GWh|
|Source of electricity||SO2 a||NO2 b||TSP c||CO d||VOCs e|
a Sulfur Dioxide contributes to air pollution-related health effects by reacting in the atmosphere to form sulfates, which are believed to form a significant portion of total suspended particulates (TSP) in terms of both volume and toxicity to humans (Ottinger, 1990). The major effect of sulfur oxides on ecosystems, however, is their contribution to acid rain. Externality values have been assigned by six states, averaging $1582 per ton of SO2, with a range from $0 to $4,486 per ton; only some attempt to gauge acid rain costs.
b Nitrogen Oxides such as NO and NO2, are often considered as a group (abbreviated NOx) because they are commonly produced together and can incontrovert. In the atmosphere, NOx forms yellow-brown clouds which add to haze and smog, contribute to climate change when they convert in the atmosphere to form the potent greenhouse gas nitrous oxide (N20), react to form tropospheric ozone (O3), the major component of smog, and precipitate out as acid rain. The contribution of nitrogen oxides to ozone formation merits particular attention because O3 is a significant contributor to forest and crop damage, and has also been found to cause respiratory problems (90% of inhaled O3 is never exhaled) (Ottinger, 1990). Externality values have been assigned by six States, averaging $5008/ton, with a range from $850 to $9120 per ton.
c Particulates, abbreviated TSP (total suspended particulates), are very fine solid particles suspended in air; They have diverse sizes and chemical properties, with the smaller particles being particularly hazardous to human health since they remain in the air longer and can not be filtered out by the respiratory system (Ottinger, 1990). Some particulates (such as dust, soot, and radioactive isotopes) are emitted directly into the air, while others (such as sulfates) form after reactions between compounds in the atmosphere. Particulates typically remain in the air for a week to forty days before they are deposited by rain, or combine to form larger particles which settle out. A comprehensive review of US and European studies found a high correlation between mortality rates and TSP levels (Dockery and Pope, 1993 and 1994). Externality values have been assigned by six States, averaging $3036/ton, with a range from $333 to $4,608/ton.
d Carbon Monoxide is a gas formed from the incomplete combustion of fossil fuels. Carbon monoxide can cause headaches in people, and place additional stress on those individuals with heart disease (Ottinger, 1990). The two states that have assigned externality values to CO give it $960 and $1,012 per ton.
e Volatile Organic Compounds are actually a diverse class of air pollutants made up of hundreds of compounds which all contain hydrogen and carbon. Methane, the simplest of the volatile organics, is a potent greenhouse gas, but is unreactive in the atmosphere. The rest of the VOCs, on the other hand, are highly reactive and combine with nitrogen oxides to produce major components of smog and tropospheric ozone. Although volatile organic compounds are produced in small amounts, they have been assigned a high externality value of $3,085/ton by the one state that has assessed them.
Carbon Dioxide Emissions
Table A5. Carbon dioxide emissions per GWh of electricity produced over the total fuel cycle. A typical person uses about a tenth of a GWh of electricity in a year (Pimentel et al., 1994 a). Figures are adapted from USDOE (1989 b), and USEPA (1994).
|Source of electricity||Tons of CO2/GWh|
|Coal||751 - 964 a|
|Natural gas||484 - 590 a|
|Hydroelectric||3.1 - 10.0 b|
|Biomass||see footnote c|
a Coal and Natural gas: The combustion of all fossil fuels produce large amounts of carbon dioxide. Coal, however, contributes far more CO2 per GWh of electricity than other power sources. Coal-fired plants are responsible for 84% of electric utility carbon emissions in the US (Ottinger et al., 1991). Gasified coal produces slightly less CO2 per unit of electricity produced (751 tons/GWh), while natural gas that is not derived from coal produces only about half the amount that traditional coal combustion emits (484 tons/GWh).
b Nuclear, Hydroelectric, Wind, and Photovoltaics: These energy sources have no direct emissions of CO2 during electricity generation. Rather, the emissions stem from fossil fuel burning during other parts of the fuel cycle (uranium mining and processing, turbine construction, etc.). The carbon emissions would therefore be much lower if renewable energy sources were used which had small rates of CO2 emissions. The scale of hydropower affects the amount of CO2 produced: the lesser value corresponds to large hydro and the greater value to small scale hydro.
c Biomass: If forests were harvested sustainably, the use of biomass for electricity would yield no net CO2 increase in the atmosphere because the amount of carbon emitted during combustion equals the amount that would be removed from the atmosphere during regrowth. However, if energy crops were grown using industrial agricultural methods, the CO2 emitted per unit of electricity produced may be significantly greater than zero due to the energy required for fertilizers, pesticides, and planting and harvesting.
Occupational Health and Safety
Table A6. Occupational fatalities and lost work days for major sources of electricity. Data on natural gas, hydroelectricity, and biomass are not available. Adapted from Ottinger et al. (1991).
|Source of electricity||Fatalities (deaths
|Lost work days
(1000 worker days
lost per GW/yr)
|Coal||1.19||1.94 - 56.0|
|Natural gas||low a||low|
|Nuclear||0.16 - 2.1||0.15 - 1.95|
|Photovoltaics||less than 0.01||1.5|
|Wind||0.28 - 0.44||0.82 - 1.36|
a Parallel figures were not available for natural gas or biomass-fueled electricity. However, it has been calculated that the harvesting of forest biomass has an occupational injury and illness rate that is 14 times higher than underground coal mining and 28 times higher than oil and gas extraction, per kilocalorie of energy produced (Pimentel et al., 1984).
Energy Return on Investment
Table A7. Total energy inputs required for the construction of electricity-generating facilities that produce 1 billion kWh/yr of electricity. The energy return on energy investment is an energy input/output ratio: the amount of energy that is produced over the unit's 30-year life span, divided by the amount of energy consumed during construction. Energy to extract the fuel is not included in the figures, but is discussed in the notes on each fuel source.
|Source of electricity||Energy
(kWh x 109)
on energy investment
|Coal||0.12||less than 8:1 a|
|Natural gas||NA||NA b|
|Nuclear||0.03||less than 5:1 c|
|Hydroelectric||0.02||less than 48:1 d|
|Photovoltaics||0.11||more than 9:1 f|
a Coal: The energy return ratio of 8:1 (Pimentel et al., 1994 a) is a significant overestimate because it does not take into consideration the energy required to extract the coal. Although more efficient technologies may increase this value, these gains could be balanced by the decreased plant efficiencies that come with more stringent pollution controls.
b Natural gas: Information on the energy investment for natural gas plants is not available.
c Nuclear: The 5:1 ratio (Pimentel et al., 1994 a) for nuclear power is an overestimate for a few reasons. First, this value does not include the significant energy required for uranium mining and processing when this is included in the calculations. Second, the 5:1 ratio does not take into consideration the large amounts of energy required to process the radioactive waste and eventually decommission the nuclear reactor. Although other forms of electricity generation, especially coal plants, have additional energy requirements to dispose of their associated waste, the energy consumed is very small compared to what is required to deal with radioactive waste.
d Hydroelectric: Hydropower has by far the most favorable energy return on investment, with a value of 48:1 (Pimentel et al., 1994 a). However, such returns should not be expected from future dams because the most favorable sites have already been developed or set off-limits. The future ratio may be expected to be closer to 15:1 which has been calculated for Europe (Pimentel et al., 1994 a).
e Wind: The energy return on investment ratio of 5:1 is likely to increase for wind power as designs improve and lighter-weight materials are incorporated (Pimentel et al., 1994 a).
f Photovoltaics: PV systems have a 9:1 energy return ratio when their efficiencies are about 7.5% (Pimentel et al., 1994 a). However, this estimate is low because more recent PV systems are achieving 10-15% efficiencies in the field, and prototype modules are reaching much higher efficiencies in the laboratory. A more likely figure for energy return on investment, therefore, may be 17:1 (Pimentel et al., 1991).
g Biomass: Biomass has a very low energy output to input ratio of 3:1 for natural forest biomass (3 tons of woody biomass can be harvested per hectare, but 33 liters of diesel fuel per hectare are used in harvesting and transporting the wood, and 70% of the 13.5 million thermal kcal are lost in the conversion to electricity- a value similar to coal plants; Pimentel et al., 1994 a). Ratios for crops grown specifically for electricity production vary greatly but would probably be even lower. Although yields for energy crops would be higher per acre than natural forest biomass, these gains would be offset by the greater energy inputs associated with intensive agriculture (Pimentel et al., 1994 b).
Current Market Price Table A8. Current market price for sources of electricity in the US. Price ranges are due to differences in the technology employed, geographical region, subsidies, etc. Adapted from Pimentel et al. (1994 a), and Flavin and Lenssen (1994).
|Source of electricity||Current Market Price
|Coal||3 - 6|
|Natural gas||4 - 6|
|Nuclear||5 - 21|
|Wind||5 - 7|
Estimated Externality Costs
Table A9. Externality costs were adapted from Kennedy et al., 1991, and. The range cited is an indication of the large variations of estimates within the literature.
|Source of electricity||Externality Cost
|Coal||0.04 - 25.8|
|Natural gas||0.09 - 2.8|
|Nuclear||0.001 - 37.8|
|Wind||0 - 0.15|
|Photovoltaics||0 - 0.4|
|Biomass||0 - 0.7|
Impacts of Household Electricity Use
Table A10. Adapted from Brower and Leon (1999).
|Impact type||Amount caused by all consumer activities||Percent caused by electricity consumption||Amount caused by electricity consumption|
|Greenhouse gases||28,461 lb/yr.||20.8%||5913 lb/yr.|
|Common air pollution||1120 lb/yr.||18%||202 lb/yr.|
|Toxic air pollution||64 lb/yr.||0.7%||0.4 lb /yr.|
|Water pollution||1391 lb/yr.||6.5%||90 lb /yr.|
|Water use||767 gallons/day||2.5%||7001 gallons/yr|
|Terrestrial habitat alteration||88,920 ft2||0.3%||267 ft2/yr.|
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