The Importance of Geothermal Power
Guest post by John Malone
In the world of renewables, most of the attention is on the wind and the sun. Geothermal power just hasn’t gotten the same respect. That could be changing, as both the Obama Administration and Silicon Valley are considering the heat under the ground as a potentially huge source of clean, domestic U.S. energy, but recent setbacks are calling into question how much geothermal can contribute. Given the potential benefits, we should be doubling our efforts to make geothermal a viable power source for the U.S.
Some background: All thermal power plants use the same basic process. A heat source (burning coal or gas, uranium, concentrated solar energy) is used to turn water into steam, and the energy released turns a turbine that produces electricity. What sets geothermal apart is that the steam comes directly from the ground. Water percolates down through cracks in the ground and is heated to the boiling point by hot rocks underground (in some cases coming back up as a geyser — think Old Faithful), and the resulting steam is drawn up via a well to a turbine.
This makes for, in principle, the ideal alternative energy source. Geothermal power releases virtually no CO2 or pollutants. Crucially, geothermal provides baseload power — wind and solar power are better suited as peaking technologies, as they are dependent on energy sources that wax and wane over the course of a day. Geothermal power is on 24 hours a day, 365 days a year (geothermal power plants can have utilization rates up to 98%). And from a national security angle, the promise of geothermal is obvious: There is no more domestic source of energy than the actual ground underneath us.
There’s one problem, though. There are only a few places in the U.S. where you can find shallow groundwater hot enough to get steam directly from the ground. Engineers and geologists are therefore looking at a new way to tap underground heat. Enhanced Geothermal Systems (EGS) make use of the fact that, if you drill deep enough, any bedrock in the world gets hot enough to boil water. Basically, EGS involves drilling a well into deep, hot, dry rock; drilling a second well nearby to the same depth; fracturing the rock between those two wells enough to allow water to pass between them; and then pumping water down the first well and allowing it to percolate through the hot fractured area to the second well, where it will come back to the surface as superheated steam. The potential for EGS in the U.S. is enormous. A 2006 MIT report concluded it could provide 100,000 MW of power by 2050.
EGS is not without its drawbacks. Cost is the main hurdle. Oil and gas companies now measure well depths in miles, but these are wells drilled through relatively soft rock, not the hard granites that are best suited for EGS. If not managed properly, rocks could lose their heat — eventually, pumping water through a hot rock system could bring the heat gradient down to the point that new wells need to be drilled. There has also been some concern about earthquakes. In 2006, an EGS pilot project in Switzerland set off a 3.4 magnitude quake.
That said, these hurdles are all surmountable, and given the huge benefits it could bring, there is already a surge in investment — both public and private — in EGS. Google laid down an $11 million investment for early-stage research. Perhaps most encouraging is the interest shown in EGS by our Nobel Laureate Secretary of Energy, Steven Chu. Obama’s stimulus plan set aside $400 million for pure geothermal R&D. And it’s looking like EGS wouldn’t need too much more of an investment. A recent NYU study found that as little as $3 billion in R&D development could make EGS cost-competitive with fossil fuel plants.
The widespread application of EGS is still a ways off. But geothermal, whether traditional or EGS, should be used alongside technologies like wind and solar to diversify our renewable base. There is no silver bullet in renewable energy. It’s better to think in terms of silver buckshot, where a collection of solutions add up to a big impact. We should do our best to make sure that one of those solutions is the one right under our feet.
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