The crust stretched, thinned, and broke into blocks that tilted to form mountains on the high side while filling and leveling basins with sediment and water, as John McPhee memorably described in his 1981 book, Pelvis and spine. From a geothermal perspective, the important thing is that all this stretching and tilting brought the hot rocks relatively close to the surface.
There’s a lot to love about geothermal energy: it offers a virtually limitless, always-on, emission-free source of heat and electricity. If the US could capture just 2% of the thermal energy available 2-6 miles below the surface, it could produce more than 2,000 times the country’s total annual energy consumption.
But due to geological limitations, high capital costs and other problems, we barely use it: today it accounts for 0.4% of US electricity production.
To date, geothermal power plant developers have largely been able to tap into only the most promising and economic locations, such as this stretch of Nevada. They needed to be able to drill into porous, permeable, hot rocks at relatively shallow depths. The permeability of the rock is important to allow water to move between two human-drilled wells in such a system, but it is also a feature often lacking in other favorable areas.
Beginning in the early 1970s, researchers at Los Alamos National Laboratory began to demonstrate that we could circumvent this limitation. They found that by using hydraulic fracturing techniques similar to those currently used in the oil and gas industry, they could create or widen cracks in relatively hard and very hot rock. Then they could add water, essentially engineering radiators deep underground.
This “enhanced” geothermal system basically works like any other, but it opens up the possibility of building power plants in places where the rock is not yet permeable enough for hot water to circulate easily. Researchers in the field have argued for decades that if we lower the cost of such methods, it will open up vast new areas of the planet for geothermal energy development.
A prominent 2006 MIT study estimated that with an investment of $1 billion over 15 years, advanced geothermal plants could produce 100 gigawatts of new power on the grid by 2050, putting them on par with more popular renewables. (By comparison, the U.S. has about 135 gigawatts of solar and 140 gigawatts of wind installed.)
“If we can figure out how to extract heat from the ground in places that don’t already have a natural circulating geothermal system, then we’re going to have access to a really huge resource,” says Susan Petty, author of the report and founder of Seattle-based AltaRock Energy. the first startup with advanced geothermal energy.