What
are the environmental benefits and issues related to
geothermal energy?
6.1. Why is geothermal energy considered to be renewable?
Geothermal systems produce a natural source of steam and hot water from aquifers of hot water heated by hot rocks underground. At the Earth’s core, 4,000 miles deep, temperatures can reach upwards of 9,000°F (5,000°C). Geothermal resources can be considered renewable “on timescales of technological/societal systems and do not need geological times for regeneration as fossil fuel reserves do.” The National Energy Policy Act of 1992 and the Pacific Northwest Electric Power Planning and Conservation Act of 1980 both define geothermal energy as a renewable resource. Earth’s heat is a constant source of energy that is essentially inexhaustible, and rainwater and snowmelt continue to feed the underground thermal aquifers. Heat has been radiating from the center of the earth for some 4.5 billion years, and it is estimated that it will continue to radiate for billions of years into the future.
6.2.
How do geothermal plants compare to fossil fuel-fired power plants?
Unlike fossil fuel power plants, no smoke is emitted from geothermal power plants, because no burning takes place; only steam is emitted from geothermal facilities. Emissions of nitrous oxide, hydrogen sulfide, sulfur dioxide, particulate matter, and carbon dioxide are extremely low, especially when compared to fossil fuel emissions. The binary geothermal plant, which currently represents around 15% of all geothermal plant capacity, along with the flash/binary plant, produce nearly zero air emissions. Even dry steam plants, which are considered to have the highest levels of air emissions, are considered environmentally benign compared with fossil fuels. For example, Lake County, California, downwind of The Geysers, has met all federal and state ambient air quality standards for almost 25 years. There are 21 power plants at The Geysers, comprising a significant complex of electric generation facilities, yet even despite this, air quality is excellent. At The Geysers, air quality has even improved as a result of geothermal development because hydrogen sulfide, which would ordinarily be released naturally into the atmosphere by hot springs and fumaroles, instead now passes through an abatement system that reduces hydrogen sulfide emissions by 99.9%. (1) See also Myth #2.
Table 1: Emissions from Geothermal Facilities Compared with Coal Facilities
| Emission |
Nitrogen oxide (NOx) |
Sulfur Dioxide (SO 2)* |
Particulate Matter (PM) |
Carbon Dioxide (CO 2) |
| Sample Impacts |
lung irritation, coughing, smog formation, water quality deterioration |
wheezing, chest tightness, respiratory illness, ecosystem damage |
asthma, bronchitis, cancer, atmospheric deposition, visibility impairment |
global warming produced by carbon dioxide increases sea level, flood risk, glacial melting |
Geothermal emissions
(lb/MWh) |
0 |
0–0.35 |
0 |
0–88.8 |
| Coal emissions (lb/MWh) |
4.31 |
10.39 |
2.23 |
2191 |
| Emissions Offset by Geothermal Use (per yr) |
32 thousand tons |
78 thousand tons |
17 thousand tons |
16 million tons |
While most geothermal plants do not emit sulfur dioxide directly, when a small amount of hydrogen sulfide is released as a gas into the atmosphere, it eventually changes into sulfur dioxide and sulfuric acid. Therefore, any sulfur dioxide emissions associated with geothermal energy derive from hydrogen sulfide emissions.
6.3. Can geothermal energy
can help reduce global warming?
Geothermal power plants emit essentially no or very low levels of one of the most significant gases known to induce global warming: carbon dioxide. According to the Energy Information Administration (EIA), carbon dioxide accounts for 83% of U.S. greenhouse gas emissions; nitrous oxide and methane make up most of the remainder. (2) Experts generally agree that global warming poses significant environmental and health impacts, including flood risks, glacial melting problems, forest fires, increases in sea level, and loss of biodiversity. (3) Geothermal power plants emit none or only a small fraction of the carbon dioxide emitted by traditional power plants on a per megawatt hour basis, and can help reduce the overall release of carbon dioxide into the atmosphere and emit no nitrous oxides or methane. Binary, air-cooled power plants have effectively zero emissions.
6.4. Can geothermal energy
can offset other environmental impacts?
Wastewater that might otherwise damage surface waters is being used to recharge The Geysers geothermal reservoir and irrigate local land. In addition, electricity generation from geothermal resources eliminates the mining, processing, and transporting required for electricity generation from fossil fuel resources. Finally, research into the extraction of minerals from geothermal water is showing great promise. Use of extraction technology would allow for the production of minerals without the environmental impacts of mining. ( 4)
6.5. How much land does geothermal energy production require?
According to the U.S. Department of Energy, geothermal energy uses less land than other energy sources, both fossil fuel and renewable. No transportation of geothermal resources is necessary, because the resource is tapped directly at its source. Over 30 years, the period of time commonly used to compare the life cycle impacts from different power sources, a geothermal facility uses 404 m 2 of land per gigawatt hour, while a coal facility uses 3632 m 2 per gigawatt hour. ( 5)
Figure 24: 30-Year Land Use Comparison
6.6.
Aren’t geothermal plants noisy?
Noise from normal operation of power plants comes from cooling tower fans and is very low. A variety of noise muffling techniques and equipment are available for geothermal facilities. During drilling, temporary noise shields can be constructed around portions of drilling rigs. Noise controls can be used on standard construction equipment, impact tools can be shielded, and exhaust muffling equipment can be installed where appropriate. Turbine-generator buildings, designed to accommodate cold temperatures, are typically well-insulated acoustically and thermally, and equipped with noise absorptive interior walls. ( 6)
Figure 25: Flowing Steam Through a Silencer at Coso, a Double Flash Plant in California
6.7. Don't geothermal plants consume water?
Air cooled geothermal power plants do not consume any water. Geothermal plants that use water for cooling typically use geothermal water or steam condensate and not fresh water. Geothermal power plants could also produce potable water from geothermal condensate, and at least one such plant was designed recently for use in East Africa. (7)
6.8. How can geothermal energy help reduce health impacts and healthcare costs?
An analysis by Abt Associates assesses the health impacts related to power plant emissions. Reducing power plant nitrogen emissions by one million tons and sulfur emissions by four million tons as of 2010 would mean:
- The number of related deaths would be reduced by 8714, with an associated healthcare savings of almost 53 million
- The number of related cases of chronic bronchitis would be reduced by 5997, with an associated healthcare savings of almost 2 million
- The number of related heart attacks would be reduced by 13,924, with an associated healthcare savings of almost 2 million
Because geothermal use offsets emissions of nitrogen and sulfur produced by fossil fuel power plant, geothermal can help reduce the healthcare effects and related costs. ( 8)
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