Environmental Concerns
From Thermal-FluidsPedia
Compared to fossil fuels, geothermal energy produces much less pollution. Current geothermal fields produce 60% less carbon dioxide that a natural gas fueled electricity-generating power plant produces, (a) with none of the nitric oxide (NOx) gases and much lower sulfur compounds than coal and oil power plants. Geothermal plants do, however, produce trace amounts of hydrogen sulfide, a gas that smells like rotten eggs-- usually associated with hot mineral springs-- and which can be harmful at high concentrations. Some arsenic, mercuric and other toxic gases are also released by the plant. Newer binary- and combined-cycle geothermal plants inject these gases back into the geothermal wells and produce virtually no air emissions.
Geothermal production can adversely affect the environment by degrading of geothermal features, promoting ground subsidence, and increasing seismic activities, all of which occur as a result of declining reservoir pressures. Another concern is the release of hot waste water containing significant amounts of toxic substances such as lithium, boron, mercury, and arsenic into existing waterways. This impact can be mitigated by controlling reservoir pressure through adjusting the discharge rate and reinjecting the geothermal fluid back into the ground. Binary plants work in this fashion and typically have no releases.
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References
(1) Toossi Reza, "Energy and the Environment:Sources, technologies, and impacts", Verve Publishers, 2005
Additional Comments
(a) Combustion of bituminous coal emits about 900 kg of carbon dioxide per MWh; the corresponding numbers for natural gas and geothermal plants are 300 and 120 kg per MWh.
Further Reading
Dipippo, R., Geothermal Power Plants: Principals, Applications and Case Histories, Elsevier, 2005.
Dickson, M. H., Fanelli, M., Geothermal Energy: Utilization and Technology, Stylus Pub., 2005.
Ochsner, K, Geothermal Heat Pumps: A Guide for Planning and Installing, Earthscan Ltd, 2007.
Gupta, H. , and Roy, S., Geothermal Energy: An Alternative Resource for the 21st Century, Elsevier, 2007.
Geothermics, Direct Science Elsevier Publish. Company, publishes articles on geothermal energy resources and technologies.
Geotimes, Journal of the American Geological Institute.
Geo-heat Center Quarterly Bulletin, covers how-to articles on various geothermal applications and equipment, progress in research and development activities of direct heat utilization
Journal of Volcanology and Geothermal Research, an international journal on the geophysical, geochemical, petrological, economic, and environmental aspects of volcanology and geothermal research.
External Links
National Renewable Energy Laboratory Geothermal Energy Program (http://www.nrel.gov/geothermal).
Idaho National Laboratory Geothermal Program (http://geothermal.id.doe.gov).
US Department of Energy Geothermal Technology Program (http://www1.eere.energy.gov/geothermal).
California Energy Commission ((http://www.energy.ca.gov/geothermal).
Geothermal Resources Council (http://www.geothermal.org).
Geothermal Energy Association (http://www.geo-energy.org).