Climate interview 3: Hot Rock Geothermal
Please talk about Geothermal or, as you call it Hot Rock Energy.
I find it fascinating and, quite frankly, have not heard much about this source of energy.
It’s because “geothermal” has an image problem rather like electric cars once had. It took the success of a 1997 gasoline-electric hybrid called the Prius to help people think ahead to an all-electric car without defaulting to an image of a golf cart of limited utility, not suitable for the freeways. Hearing geothermal, we often pop up a mental image of a sulfurous hot spring and wrinkle our nose. Too many people think that geothermal is just piping near-surface hot water around to heat some buildings—say, Idaho’s State Capitol buildings in Boise. This in turn makes you think that geothermal electrical power is a special case, nice for Iceland but not more generally. That, however, is your grandfather’s notion of geothermal, badly out of date. See the report put out by a panel of eighteen experts that MIT assembled in 2006 to evaluate Hot Rock Energy as an industrial-strength solution for C-free electricity. The experts said it could yield a thousand times more than our present overall energy use. How polluting? Close to zero. 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 Nation¬al 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 com¬fort¬able 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.
9. What would be the Hot Rock timetable, to get enough to retire the supertankers and coal trains? What needs to be done to get us going in this direction?
There have been various research projects around the world since 1970 that have demonstrated the deep heat mining techni¬ques. Serious power product¬ion, however, is only getting started. In France, they are getting near-commercial-sized yields at depths of 4 to 5 km. There are some projects in southern Germany and northern Switzerland. Australia has quite a few proof-of-concept projects limping along on private money.
The only hesitation that I have about Hot Rock Energy for 2020 is that there is simply not enough experience with it yet, compared with the experience of running hundreds of nuclear plants over fifty years time. Even though merely combining two tested techniques, deep drilling/stimulation and steam power plant, there will be beginners’ errors to discover. We must do that quickly.< The capital costs per megawatt-hour are similar to those of a new coal plant. They are mostly drilling costs, which ought to fall with a real market for drilling services. Indeed, until opening up those fractured rocks in the depths with the initial hydraulic injection, you don’t know what size power plant to order for the well head. That might cause private capital to hesitate, suggest¬ing a proper role for government money to do the initial Deep Heat farms and then sell the good ones off to industry.
If I were the 2020 czar, I’d place an order for twenty deep drilling rigs and fund fifty Deep Heat farms in order to find the beginner’s errors and the efficient combinations. We urgently need to know if Hot Rock Energy can be ramped up worldwide to thousands of units. That’s when we can start cancelling orders for more nuclear power plants.
