Ringside – Geothermal Energy: A Huge Wildcard

If geothermal energy is a niche source of power in California, then it is in good company. In 2025, geothermal energy generated 10,908 gigawatt-hours (GWh) of electricity in California. That puts it well above biomass (4,226 GWh), and sort of in the ballpark with wind (15,172 GWh) and nuclear (17,575 GWh). California’s biggest sources of electricity last year, not surprisingly, were solar PV (53,642 GWh) and natural gas (73,750 GWh).

There are advantages to geothermal power that elude other categories. Unlike wind and solar, but like nuclear and natural gas generating plants, when it is running, geothermal provides uninterrupted baseload power. In 2025, California’s active geothermal plants ran at 46 percent of capacity, a rate of continuous runtime only eclipsed by nuclear at 84 percent. As intermittent sources of energy, the state’s wind turbines ran at 27 percent of their capacity and solar photovoltaic at 26 percent. Natural gas fueled generators, which, like geothermal, are turned off when solar electricity is generating surplus electricity, only ran at 22 percent of their capacity.

The pathway to electricity abundance is wide. An obvious opportunity is to simply upgrade natural gas power plants so that advanced combined cycle designs can convert up to 65 percent of the BTU energy of the natural gas fuel into gigawatt-hours of electricity. Then, run them as baseload plants with 90 percent uptime, instead of the paltry 22 percent that California’s beleaguered fleet delivered last year. If CO2 is a concern, harvest it or bury it. Problem solved.

Solar electricity is another obvious opportunity, with particular appeal because it can be decentralized onto private property. Imagine a future where decentralized PV panels generate electricity buffered by millions of grid connected EVs using AI to buy and sell electricity for their owners. No more daytime surpluses, and with the PV/EV systems integrated with the homes and businesses that consume electricity, far less transmission grid upgrades.

Nuclear energy, whether it’s keeping Diablo Canyon open, building more huge reactors, or proliferating the many small reactor designs as they become commercially available, is yet another wide open lane on our road to electricity abundance. But what about geothermal energy? Can it also be scaled up?

According to the U.S. Bureau of Land Management, California has “two of the largest geothermal reservoirs in the United States, the Salton Sea resource area and the Geysers [mostly in Mendocino County], with an estimated generation capability of 2,200 MW and 1,800 MW respectively.” At 100 percent uptime, these 4 gigawatts of baseload capacity would produce up to 35,000 gigawatt-hours per year.

That’s about it. A 2014 analysis conducted by the Geothermal Energy Association estimated the upper potential of California’s geothermal fields slightly higher at 5.3 gigawatts, which at 100 percent uptime would produce around 46,500 gigawatt-hours per year. A geothermal field is being investigated in Modoc County in California’s northeast. New aerial survey technologies are being used to map geothermal resources around the Salton Sea and elsewhere in the state. These and other new surveys of additional sites suggest that, best case, conventional sources for geothermal electricity in California, fully developed, might deliver up to 50,000 gigawatt-hours per year. But what about so-called enhanced geothermal?

This is where geothermal gets more interesting. Conventional geothermal power relies on volcanic hotspots where naturally occurring underground reservoirs of hot water or steam are tapped to spin a turbine before being condensed and pumped back down. Several factors limit the potential of conventional geothermal electricity generation, starting with the fact that there are limited sites where volcanic heat and underground water are co-located. Other problems are caused if steam is withdrawn too fast, which lowers the pressure, or if reinjected water cools the underground reservoirs faster than the hot rock can conduct heat back into them. Also, by circulating the underground water, its high mineral content can clog the supply fissures and the pipes to and from the turbines.

Enhanced geothermal technologies cope with these limitations in differing ways. One promising approach is to identify hot rock, even if it is 10,000 feet deep and has no accompanying aquifer, and drill two deep wells. Using horizontal drilling techniques perfected by the oil industry, an injection well is connected to a production well. Water is pumped down into the hot rock, heated, then comes up the production well to run through a heat exchanger before going back down the injection well. The heat exchanger is used to transfer thermal energy to a fluid with a lower boiling point that vaporizes to turn a turbine. One of the leading companies developing this approach is Fervo Energy.

Another ambitious approach is to go deeper, much deeper, using novel boring technologies: directed energy waves that purportedly will melt and vaporize rock. When you reach a depth of 50,000 feet or more, you can tap a hot spot almost anywhere on earth, and the temperatures down there reach 750 degrees or more. Water injected into a hole this hot will vaporize into “supercritical fluid,” a hybrid state that exhibits properties of liquid and gas, and can carry up to ten times the energy per unit of mass than conventional steam. A company working on this approach is AltaRock.

Finally, there is an engineering approach that attempts to avoid the corrosive hazards of the first two examples, which both circulate water through exposed rock underground. Instead, the water is injected down the center core of a pipe, then brought back to the surface in the outer core of the same pipe. In this coaxial configuration, a heat conducting material coats the outside of the underground pipe, and by the time the water reaches the surface in this closed loop, it is hot enough to drive a steam turbine. While this technology is limited to sites where underground heat of around 400 degrees is relatively close to the surface – 3,000 to 10,000 feet down – it does not require an underground reservoir. A company working on this approach is XGS Energy.

It is too soon to know whether these or other approaches to enhanced geothermal energy will become commercially competitive. But if they do, this source of electricity could rival everything else. It is clean, it will never run out, and at least theoretically, the number of sites where it can be deployed far exceeds what would be needed to generate the additional thousands of terawatt-hours our dawning electric age shall demand. Stay tuned.