What is Geothermal Energy?
Answer: Geothermal energy is heat (“thermal”) derived from the earth (“geo”). It is the thermal energy contained in the rock and fluids, that fill the fractures and pores in the rocks that form the earth’s crust.
How does geothermal heat get up to the earth’s surface?
Answer: The heat from the earth’s core continuously flows outward. It transfers (conducts) to the surrounding layer of rock, the mantle. When temperatures and pressures become high enough, some mantle rock melts, becoming magma. Then, because it is lighter (less dense) than the surrounding rock, the magma rises (convects), moving slowly up toward the earth’s crust, carrying the heat from below.
Sometimes the hot magma reaches all the way to the surface, where we know it as lava. But most often the magma remains below earth’s crust, heating nearby rock and water (rainwater that has seeped deep into the earth) – sometimes as hot as 700 degrees F. Some of this hot geothermal water travels back up through faults and cracks and reaches the earth’s surface as hot springs or geysers, but most of it stays deep underground, trapped in cracks and porous rock. This natural collection of hot water is called a geothermal reservoir.
Why is geothermal energy “environmentally friendly”?
Answer: Unlike coal fired and natural gas fired power generation plants, the state of the art geothermal binary cycle plant produces virtually no emissions. When compared to natural gas, a 100 MW geothermal power generator offsets 190,000 pounds of nitrogen dioxide and sulfur dioxide per year. Additionally, it eliminates 780 million pounds of CO2 emissions. The reduction in emissions, when compared to coal fired plants, is even greater. The binary cycle technology was pioneered at Raft River, Idaho in the early 1980s.
Why is geothermal considered a renewable energy resource?
Answer: All types of geothermal energy are renewable as long as the rate of heat extraction does not exceed the rate at which the thermal reservoir it depends upon is renewed by heat from the earth’s magna. Geothermal reservoirs that tap the earth’s heat for energy production typically have 30 to 50 year life as the plant’s equipment wears out. Indeed, the world’s first geothermal power plant at Larderello, Italy was commissioned in 1913 and is still producing. The Geysers, California facility has been in production since the early 1960s.
Does technology exist to extend reservoir life?
Answer: Yes, in particular with binary plants since the water produced from the fracture system can be re-injected back into the fracture system and reheated by the source rock. Currently, Calpines, the owner of Geysers, is constructing a $163 million, 41-mile pipeline to move the effluent water from the City of Santa Rosa’s sewage system for injection into the geothermal reservoir. The Raft River property of US Geothermal Inc. (“USGEO”) will involve a binary system to save and re-inject water back into the fractures for reheating. The scheduled reservoir modelling will identify where to position injectors for the maximum benefit.
Why has there not been greater development of U.S. geothermal capacity?
Answer: The development of geothermal power thorough the 1990s has been impeded by two factors: location and cost. In respect of location, most geothermal reservoirs are located in the Western States and specifically in areas which enjoyed excess electrical capacity. For example, Raft River in Idaho and the Newberry Caldera in Oregon are within the Bonneville Power Authority (BPA) system, which distributes hydropower from the Columbia River dams. Local electrical distributors like Idaho Power, and Pacific Power could service their clients by purchasing from the BPA the lowest cost electricity in the USA.
In respect of costs, prior to recent technological advances, the cost of developing geothermal reservoirs, building generators and operating them was between 6 cents and 8 cents per kilowatt hour (Kwh). The major sources of new electrical power generation in the 1990s and until recently was coal and natural gas. These sources were competitive in the 4 to 6 cent per Kwh range.
Where can I find more information on geothermal resources, specifically electrical generation?
Answer: Some excellent sources of information include:
- Office of Energy Efficiency and Renewable Energy, www.eren.doe.gov
- Geothermal Resource Council, www.geothermal.org
- Geothermal Energy Association, www.geo-energy.org
For more questions and answers about the definition, costs and sources of geothermal energy, visit the U.S. Department of Energy Geothermal FAQ page.