A week ago, the USGS updated its official estimates of U.S. geothermal energy resources for the first time in over 30 years. During the past three decades, we've made significant progress on technology to exploit geothermal energy in areas where there's plenty of heat in the ground, but no natural hydrogeologic plumbing system to help us exploit it. In other words: We are much better at cracking rocks underground than we used to be.
Assuming that this type of rock-cracking technology (aka "enhanced" geothermal systems) continues to work out as well as expected, the new study estimates that the equivalent of 50% of the nation's current electricity supply is just sitting around in the ground in the Western U.S. That's less than the 150% of current electricity that we could get if we blanketed the windiest 6% of the nation in windmills (source), but it is still nothing to sniff at.
Here's where we should be drilling:
This map of potential enhanced geothermal resources really just shows subsurface temperatures, which means it's really a map of what's been happening in the mantle over the past 30 million years. You can see lots of tectonic features. Check out:
- Yellowstone and its associated hotspot trail, cutting a swath through Idaho
- the Rio Grande Rift, stretching up through New Mexico
- the Salton Trough at the very bottom of California - we think of the Pacific-North American plate boundary as being a strike-slip system, the San Andreas. But when you get far enough south... the Gulf of California actually has just a wee bit of rifting going on.
- the sharp transition from the part of North America overlying the cold Juan de Fuca slab, to the part of North America overlying the still-cold-but-warm-enough-to-give-off-volcanoes Juan de Fuca slab
In principle the concept is wonderful, but in practice many people will find geothermal powerplants just as objectionable as offshore drilling rigs. Are we really going to put power stations in Yellowstone Nat'l Park, or drill next to Crater Lake or Mt. Shasta? Maybe we can drill the Salton Sea area (Mexico has for some years had a geothermal power station just across the border near Mexicali, if memory serves) - still, Salton Sea geothermal waters are hot brines at depth, and create some "interesting" disposal problems when they are brought to surface ...
Scott: It doesn't work that way. As you can note from the map above, there's shallow geothermal heat covering a vast amount of the US, not just in well-known hotspots. EGS is more limited by target reservoir rock characteristics than by potential places to drill where you can find heat a reasonable distance underground.
Again, we're talking about EGS here, not conventional geothermal.
I know there's a bit geothermal plant north of San Francisco (and I can see the anomaly on the map), but remind me why it's there?
"[M]any people will find geothermal powerplants just as objectionable as offshore drilling rigs."
Another difference is that geothermal drilling doesn't burn fossil carbon (or any carbon, for that matter), whereas offshore drilling supplies more carbon to be burned. Offshore drilling kills two birds with one stone: habitat disruption AND climate change fuel.
Is this a good time to point out that at least one geothermal driller blogs?
Lab Lemming, always a good time! And he's a geologist besides!!
What do we know about the long term geological effects of large scale heat pumping? I know that Iceland has been doing it for a while; has any research been done into whether this has caused any noticeable change in the mantle?
Why yes, yes I am a geologist ;)
The area north of San Fran is an unusual system, very unlike any of the others (steam system vs. a hot water system) and currently is one of the larges geothermal production fields in the worlds, currently around 800 megawatts, nearly 2.2 at is peak in the late 80's early 90's. The rifting in SoCal is currently being exploited as we speak, Ormat Nevada will have a new plant online by the end of this year, making 50 megawatts, with one to two more planned, and several other operating plants in the area (and a few other companies down here too). I dont know of anyone wanting to come down to the Imperial Valley and try and fracture the rock, the beds of clay and sand are not really competent enough be fractured., when you get deep enough that the beds turn meta and become competent, you are down in the nasty brine (25% solids by weight) which, as Scott M. points out, are a headache to handle, on the other hand, they are very hot, around 600 F. The only problem currently with the enhanced model is cost. It takes a lot of money to drill one of these holes, roughly $1,000,000 for 1500 feet of hole, and most systems run around 3000-8000 feet, then add cost to bring in the frac equipment, make sure you have enough water on hand to pump it goes on. It is still in the exploratory stage but it is a grand idea. Geothermal is one of the only alternative energy schemes that turns a profit, the real problem the geothermal industry has right now (besides capital) is finding drilling rigs, oil has most of them.
ugh, grammer check didn't catch those: largest geothermal production fields, 2.2 Gigawatts
Do American drillers actually drill in feet, or are you just converting from meters for the locals?
All the drill steel I've ever seen - ever - comes in feet. Small rigs like mineral exploration rigs have steel that comes in 20-foot lengths. We can drill in meters, but you have to divide into some odd meterages [that's a take-off on footages] to come out with something reasonable at the end of the rod. Sample intervals need to be even - for minerals not necessarily for geothermal or oil - and sampling from the end of one rod to the beginning of another would be a waste of sampling effort, drilling cost, and assaying cost, due to possible contamination.
So yeah, feet.