Geothermal power doesn’t get the attention that wind and solar power alternatives get, but it should. Right now the installed base of geothermal energy worldwide totals about 9.5 gigawatts of output, somewhat less than wind generating capacity worldwide, and somewhat more than photovoltaic capacity worldwide. But unlike the wind and solar installations, geothermal energy runs at capacity pretty much 24 hours a day, making the actual power yielded from geothermal sources still substantially greater than wind or solar energy.
|A remote drilling rig probes the earth’s crust.
Today we caught up with Susan Petty, President of the start-up Altarock, a company formed to develop “enhanced geothermal” generating stations using new technology primarily coming from the oil drilling industry. And our main question was how much more geothermal energy is out there, and how much of it can be economically tapped.
To-date geothermal systems have relied on existing underground reservoirs of geothermally heated water, which they have tapped with wells that bring this heated water up, under pressure, using the steam to drive an electric turbine. This technique is cost-effective, but limited to the relatively rare areas where geology has delivered a source of naturally heated water fairly close to the earth’s surface. Virtually all existing geothermal plants rely on these preconditions, although many of them now inject water from the surface into the heated underground formations.
Enhanced geothermal is another ballgame entirely. Instead of finding ready-made reservoirs of geothermally heated water, the developer looks to “mine the heat” present at various depths throughout the earth’s crust, and bring the water to this heat by creating (or connecting) enough fractures and cavities beneath the earth to allow a sufficient volume of water to be injected to power a turbine. Petty explained that to-date the technology has been limited to around 2,000 feet with drilling equipment, and to about 375 degrees with pumps to bring the hot liquid back up. Today there is drilling equipment that can go to 10,000 feet in depth, and pumps capable of operating at heats in excess of 500 degrees. Because the energy contained in hot fluid increases at a greater rate than the temperature of the fluid, going from 375 to 500 (fahrenheit) will allow significantly better efficiencies.
According to a study done two years ago at MIT, there are over 100,000 exajoules of potentially exploitable geothermal energy in the earth’s crust – by comparison, the entire human race only consumed about 500 exajoules of energy in 2007 (an exajoule is approximately 1.o5 quadrillion BTUs – a convenient coincidence since back-of-the-envelope calculations can pretty much interchange exajoules and quad BTUs).
Petty at Altarock was quick to point out this entire resource cannot be accessed – but she agreed with the MIT study that somewhere between 2,300 and 23,000 gigawatts could be commercially tapped in the USA, depending on the level of research and funding enhanced geothermal technologies receive. When one considers 1,000 gigawatt-years is equivalent to 30 quadrillion BTUs – it is clear that enhanced geothermal technology could be a huge opportunity.
Not only are there remaining technological challenges, however, such as verifying these fractures can be created, that greater depths can be accessed cost-effectively, and that pumps can be used that tolerate higher temperatures, but there are political and financial hurdles. Petty noted one of the biggest obstacles is getting drilling permits. Getting approvals can take years. Another obstacle is financing. A bank financing for one of these plants (they cost roughly $3,500 per kilowatt of output) may be on a ten year note at 12% interest, whereas the “clean renewable energy bonds” which have just been broadened to include geothermal along with solar and wind projects, may only have an interest rate of 5%, on a significantly longer term. Since only 2-3 cents per kilowatt-hour is for operations and maintenance, plant financing is a bigger variable than operations costs in the ultimate price a geothermal power station can profitably sell power.
Earlier this year, Altarock received financing from Kleiner Perkins Caufield and Byers, as well as from Khosla Ventures. Here are additional links to information about geothermal power:
MIT Study “The Future of Geothermal Energy”:
U.S. Department of Energy (Geothermal Energy Technical Site):
U.S. Department of Energy (Geothermal Technologies Program)
U.S. Department of Energy (GeoPowering the West)
Sandia National Laboratories (Geothermal Research Department)
Energy Quest – California Energy Commission
GeoHeat Center (Low Temperature Uses of Geothermal Water and Heat):
International Ground Source Heat Pump Association (Geothermal Heat Pumps):
International Geothermal Association
Geothermal Resources Council (Geothermal Industry Association):
Geothermal Energy Association (Industry Trade Association):
Geothermal Heat Pump Consortium
California Department of Conservation, Department of Oil, Gas and Geothermal Resources:
California Energy Commission (Geothermal Energy):
Center for Renewable Energy and Sustainable Energy Technologies (CREST):
U.S. Geological Survey (plate tectonics)
World Bank Group (general info)
Swiss seismological service Deep Heat Mining project in Basel
Geothermal Explorers Ltd., Switzerland
European HDR project, Soultz-sous-Forets, France
Enhanced Geothermal Innovative Network for Europe, ENGINE, France
Geodynamics Ltd., HDR projects in Australia
Petratherm, Exploring for and Developing Geothermal Energy, Australia
Hot Rock Energy, Australian National University
The International Energy agency (IEA) Geothermal Energy Homepage
Fenton Hill Hot Dry Rock program, Los Alamos Nat. Lab., USA (finished)
CREGE, Centre for geothermal research, Neuchatel, Switzerland