Geothermal Energy

The idea is not to find hot water. Instead you drill down until finding hot granite that is dry. Then apply water to make steam. Though the U.S. has been lagging behind, the Hot Dry Rock concept was invented by scientists working at the Los Alamos Nation­al Laboratory in 1972. What comes up as dry steam is pumped right back down again as water, via a second well nearby. It forces through cracks in the granite, heats back up, flashes into steam, shoots up the other well to the steam turbine, which spins the electrical generator, which feeds the great electrical grid, which keeps your domestic climate com­fort­able and your car recharged.

And how do these two wells connect? Such deep rock is already fractured along onion-like sheets, ancient planes of stress from sags and folds. Mineralization has mostly filled those cracks, but high-pressure injection can force water into them, dissolving the glue and opening up passages. When the high pressure is released, many do not reseal. Sometimes the layers shift a little, and the noise from such little earthquakes serves to locate the newly-opened crack. A map of the enhanced fracture zone is built up and, when it is several km across, the second (and sometimes a third) well is drilled into it to harvest the steam.

Gushers and mud eruptions don’t come up out of the granite layers. If a sizeable earthquake fractures the well shaft, nothing happens—you just drill a new well nearby. That makes it much safer than drilling for oil or natural gas—or for storing CO2 where a leak could generate a catastrophic heat wave. There are so many obvious problems with “CO2 Capture and Store” (for example, it requires building 67 percent more coal-fired plants just because of the 40 percent efficiency hit) that I’ve concluded it is just another delaying tactic to continue the fossil fuel status quo for another thirty years.Deep geothermal is drought-proof (both hydro and biofuels could be shut down in the droughts that are forecast). Hot Rock does not involve a perpet­ual stream of truck traffic as biofuels and fossil fuels do. It is perhaps the least demanding on industry, except for manu­facturing enough tall drill rigs. What’s built above ground after the drilling rig leaves is just a simple steam plant. A 100 megawatt plant would be smaller than a two-story parking garage. Operating it is within the compet­ence of all developing countries, unlike nuclear or “clean coal” technologies. We’ve got to keep developing countries from burning their own coal or buying oil, yet still modernize–so we need to either drill them some deep holes or supply them with cheap electricity from nuclear plants in countries that already have them.

-William Calvin