|Fig. 1: Geothermal activity in Miravalles. (Source: Wikimedia Commons)|
Geothermal energy is the process of harnessing the heat generated from the center of the earth and using it for energy in the form of heat or turning it into electricity. This energy is usually harnessed from steam or hot water that is emerging from underneath the earth's surface.  The first instance of harnessing geothermal energy occurred in Tuscany Italy in 1904, when Prince Piero Ginori Conti used the heated Larderello stream to create electrical power generation on a small scale.  Since then the potential for geothermal energy generation has been discovered in over eighty countries. Uses for geothermal energy include heating for bathing/swimming, space heating, greenhouses, fish farms, electricity generation, and industry.  As of 2000, geothermal energy generation accounted for 49 TWh per year of electricity worldwide. 
However, one limitation of geothermal power plants are that they need to be built close to the source of geothermal heat. Transferring high temperature liquid and steam across long distances leads to a loss in heat and therefore energy. This limits the number of places where geothermal power plants can be profitably constructed. Heat is released from under the earth's surface typically in the form of vaporized water or hot liquid water. These power plants operate with temperatures of up to 185°C and are typically comrised of heat exchangers, turbines, generators, valves, safety circuits, and piping.  Different types of geothermal power plants are used to capture this heat and turn it into energy. Direct steam plants use a vapor dominated system where steam is transmitted by pipeline into the power plant. This steam is then used to power turbines and create electricity. Flash-steam power plants utilize flowing wells of hot liquid. This hot liquid flows into a pressurized system which turns the liquid into steam which generates electricity. Finally binary geothermal power plants take in hot water which is transformed into a second fluid which harnesses the heat and generates energy. 
Exploration for geothermal resources began in Costa Rica in 1979, largely because the oil crisis of 1973 raised prices and motivated the search for other renewable energy. From 1979 to 1994 areas of Costa Rica were being drilled to test for the best locations for geothermal power plants. Through this exploration it was determined that Costa Rica has a potential of around 900 MWe of geothermal energy.  It was eventually determined that the Miravalles geothermal field had the most potential to produce geothermal energy. Fig. 1 shows geothermal activity in Miravalles in the form of steam being released from the earth.
The first plant was constructed in Miravalles in 1994. The first electrical generation in Miravalles was 55 MWe in 1994. It has since grown to 163 MWe in 2007. Today there are 5 total geothermal units in Miravalles. Other zones in Costa Rica are being minimally explored.  As of 2010, geothermal power plant energy production at Miravalles has not significantly increased, and has leveled out at 165 MW. This accounts for 13% of the country's energy generation, with 80% coming from hydro power. Costa Rica hopes to reach 94% of its energy coming from renewable energy by 2020 with geothermal energy accounting for 12% of this. 
© Nathaniel Morris. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 I. B. Friðleifsson, "Geothermal Energy For the Benefit of the People," Renew. Sust. Energy Rev. 5, 299 (2001).
 "Proceedings of a Topical Meeting On Small Scale Geothermal Power Plants and Geothermal Power Plant Projects," Geothermal Resources Council, February 1986.
 P. Moya and A. Yock, "Assessment and Development of the Geothermal Energy Resources of Costa Rica," United Nations University, 25 Nov 07.
 R. Bertani, "Geothermal Power Generation in the World: 2005 - 2010 Update Report," Geothermics 41, 1 (2012).