Geothermal company Fervo Energy has signed a major deal to sell power to Alphabet’s Google from a Utah project that it plans to turn into the world’s largest enhanced geothermal facility.

The agreement for nearly 400 megawatts of electricity is enough to power a midsize city and would be Fervo’s largest-ever power deal. Fervo plans to begin selling power to Google in 2028 from its Cape Station project in southwestern Utah. 

Houston-based Fervo uses technology pioneered by oil-and-gas drillers to frack rocks, create geothermal reservoirs and crank out electricity. The company is spending more than $2 billion at Cape Station and expects to start delivering power to the grid later this year for the first phase of the project.

Fervo Energy shares jumped about 20% in premarket trading.