In 2013, world geothermal electricity-generating capacity grew 3 percent to top 11,700 megawatts across 24 countries. Although some other renewable energy technologies are seeing much faster growth—wind power has expanded 21 percent per year since 2008, for example, while solar power has grown at a blistering 53 percent annual rate—this was geothermal’s best year since the 2007-08 financial crisis. Graph on World Cumulative Installed Geothermal Electricity-Generating Capacity, 1950-2013 Geothermal power’s relatively slower growth is not due to a paucity of energy to tap. On the contrary, the upper six miles of the earth’s crust holds 50,000 times the energy embodied in the world’s oil and gas reserves. But unlike the relative ease of measuring wind speed and solar radiation, test-drilling to assess deep heat resources prior to building a geothermal power plant is uncertain and costly. The developer may spend 15 percent of the project’s capital cost during test-drilling, […]