‘Deep Geothermal’ Promises to Let Drillers Go Deeper, Faster and Hotter

Current geothermal plants, like this one near Calipatria, Calif., operate mostly where subterranean heat is closer to the Earth’s surface. Deep geothermal could tap more heat sources and be a game-changing alternative to fossil fuels.
PHOTO: ROBYN BECK/AGENCE FRANCE-PRESSE/GETTY IMAGES

A group of startups and researchers are developing technologies to expand the output of geothermal energy.

Geothermal plants produce steam from underground reservoirs of hot, porous rocks saturated with water, and channel it into electricity-making turbines or pipes that heat buildings. Although the energy is virtually free of carbon emissions, its adoption has been limited because drilling gets more expensive and more difficult as it goes deeper.