While wind and hydropower have emerged as the biggest renewable energy sources in the U.S., they aren’t the only ones. Geothermal, harnessing the earth’s naturally heated water to generate power, may be next for widespread use thanks to advances in technology that have been supported by impact investors.

Geothermal power uses water heated deep in the earth to turn turbines and generate electricity. Hot water near the surface is tapped, turning turbines before being pumped back into the earth. Mostly limited to the edges of tectonic plates, enhanced geothermal technology is providing access to resources that had been inaccessible.

U.S. geothermal electricity generation may increase more than 26-fold to 60 gigawatts of installed capacity by 2050, the U.S. Energy Department said in a recent report. The department called on support for enhanced geothermal technology and eased permitting.

Geothermal has far to grow. It currently produces only 0.4% of U.S. power, according to 2018 EIA statistics. Renewables account for 17%, mostly wind and hydropower. Fossil fuels — natural gas, coal and petroleum — made up 64%.

Companies are working to boost the volume of hot water that can be tapped, starting with the amount of that passes through rock. Permeability can be increased by pumping high-pressure cold water down a well into the rock. The water travels through fractures in the rock, capturing heat until forced out of a borehole as steam, and used to power a turbine. The water is then returned to the ground completing the enhanced geothermal system.

Fervo Energy is working on proprietary technology that combines directional drilling with other technologies for enhanced geothermal systems. Bill Gates-backed Breakthrough Energy Ventures and Congruent Ventures, a venture capital firm that supports sustainable projects, are backing the startup.

“Fervo is applying unconventional oil and gas technology to geothermal,” Joshua Posamentier, the co-founder and a managing partner of Congruent, told Karma. “They’re using horizontal drilling and the other tools developed by the oil and gas industry and leveraging them for geothermal.”

The success of an enhanced geothermal pilot project in Alsace, France, is promoting further development in the region and in neighboring Switzerland and Germany. The Energy Department is backing a site in Utah dedicated to research on enhanced geothermal systems.

The U.S. is the leading producer of conventional geothermal electricity, and the world’s biggest field is located at the Geysers in northern California. Calpine has 13 plants at the Geysers, producing about 725 megawatts of power, enough to supply 725,000 homes, or a city the size of San Francisco. There are geothermal power plants in six other states. 

Alaskan oil production has been declining for three decades, leading to a search for new resources and geothermal power is a promising addition to the state’s energy mix. One of the state’s U.S. senators, Lisa Murkowsky, is encouraging the development of the state’s three main geothermal resources; volcanoes along the Aleutian chain, hot springs in the interior and in the Southeast.

Geothermal power might also give Canada’s struggling oil patch a boost, the Financial Post reported. Deep Earth Energy Production Corp. plans to dig a second well this year at a site in Saskatchewan as part of the country’s first geothermal electric generating station. Unemployed oil and natural gas workers are well-placed to get jobs in the sector, according to the article.