Is large-scale geothermal energy sustainable?
Geothermal energy is a renewable energy resource as natural processes such as radioactive decay and chemical reactions occurring within the earth constantly replenish it. However, it can be sustainable only if the rate of usage matches with the rate of replenishment. Presently, geothermal energy is used for large-scale power generation and small-scale applications include home heating pumps. Geothermal power plants that use steam and hot water available directly from the ground well to run turbines are called dry steam and flash steam power plants respectively. Alternatively, if the hot water from ground is used to heat a heat exchange fluid that in turn runs a steam turbine, it is called a binary cycle power plant (Union of Concerned Scientists). Geysers in California has the largest dry steam geothermal power plant with 2000 MW capacity. But, the reservoir is dwindling due to excessive usage, and sustainable out put from the power plant is only estimated to be only 1000 MW (Stefansson). To maintain the steam reserve, treated wastewater is being injected through an intensive pipe network into hot rock bed reservoir (Union of Concerned Scientists).
Naturally occurring hydrothermal reservoirs with easy access to energy are minimal and most geothermal power plants are enhanced geothermal systems (EGS) that need deep wells to be bored thousands of meters into the ground (Clarke). Hence, there is considerable disturbance caused to the land and ground water as well. Further, gases such as hydrogen sulphide are also released into the environment. Hence, the overall process of harnessing geothermal power for large-scale power plants has considerable environmental impacts. However, with dwindling fossil fuel reserves, if appropriate measures are taken to reduce environmental impacts of EGS, geothermal power could be a sustainable resource.
How does your idea change if we consider residential heat pumps?
Considering residential geothermal heat pumps, they use only heat from the earth’s crust, which doesn’t require highly intrusive land boring activities. Also as the ground maintains a temperature of 55°F constantly in almost all regions across the globe, geothermal heat pumps are highly sustainable. Further, a wide range of configurations is available ranging from simple underground pipe systems connected to the home ventilation unit to sophisticated units with pumps and compressors (Union of Concerned Scientists). Ground source heat pumps transfer heat from ground to the home during winter providing warmth, and from home to ground during summer, thereby maintaining a comfortable indoor temperature condition. Further, ground source heat pumps can be installed in remote areas lacking access to natural gas. Hence, residential geothermal heat pumps are surely a sustainable alternative to conventional heating systems.
Works Cited
Union of Concerned Scientists. "How Geothermal Energy Works." Union of Concerned
Scientists. 22 Dec. 2014. 8 Jul. 2015. <phttp://www.ucsusa.org/clean_energy/our-energy-cho>.
Clarke, Paul. "Large Scale Geothermal Power – Could it Work?" Walden Labs.
Stefansson, Valgardur. "The Renewability Of Geothermal Energy." Proceedings
World Geothermal Congress 2000. Kyushu - Tohoku, Japan,, 10 Jun. 2000. 8 Jul.
2015 <http://www.geothermal-energy.org/pdf/IGAstandard/WGC/2000/R0776.PDF>.
