Coming soon: Advanced geothermal tech to blast open rock

The U.S. Department of Energy is making $90 million available to develop enhanced geothermal systems, up from the $10.5 million currently allotted to research.

Large geothermal systems have been developed and installed for years, including, just as a sample, a state-of-the-art 400-kilowatt system that powers a resort in Alaska, and five geothermal power plants in Iceland that produce one-fourth of the island’s power. But in the United States, at least, they remain a tiny sliver of the renewable energy pie. The reason? The technology, as simple as it is in principle, just isn’t quite there.

The difference between ordinary geothermal installations and enhanced geothermal systems is that most of the existing geothermal power generation comes from reservoirs that are limited to very specific spots that meet particular temperature conditions and have types of porous rock with water already flowing through it. But if we could safely convert more rock into a porous, aqueous environment, according to some estimates, geothermal heat could eventually account for about 10% of U.S. electricity generation.

Engineering the types of systems that could be installed more widely involves injecting fluid into hot, dry rock to make it more permeable. Basically, engineers drill a well into the rock and pump water into it. The water, under intense pressure, can cause small fractures in the rock to expand. By pumping more water, the fractures extend through the rock like capillaries, allowing the water to heat up as it comes in contact with the rock. More wells are drilled to intersect the water flowing through the newly developed fractures, to allow the fluid to circulate upward and heat to be extracted at an above-ground power plant.

The research grants, the department hopes, will stimulate better modeling of the design and productivity of wells, contribute to figuring out the best ways to fracture rock, and then optimize the power conversion once the heat is extracted. Inducing the fractures can compromise the stability of nearby land, and assessing those local impacts is key to building safe reservoirs. The rock also can potentially cool down, and understanding the thermal variation of rock over time is essential to calculating how much power the wells could realistically produce.

According to the Geothermal Energy Association, only five states currently have geothermal power plants in operation—Alaska, California, Nevada, Hawaii, and Utah—contributing about 2850 megawatts of capacity. Another 3000 megawatts, from 74 projects, of new geothermal power plant capacity are currently under development in 12 states. But the data is a year old, so some of those projects are probably online by now. With this latest push from the Department of Energy, we might see even more ambitious geothermal systems begin to pop up nationwide.


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