Thursday, August 03, 2006

Hot Rocks

This has showed up in a whole bunch of places, but most recently I saw it at Gristmill. The MIT Technology Review has an interview with one Jefferson Tester, who says that we could have unlimited geothermal power, anywhere, thanks to innovations in deep drilling brought about by the oil industry in the last 20 years.

I'm pretty wary of proposals like this (largely because in previous designs, geothermal plants built outside on natural upwelling sources tend to be net energy losers) but let a thousand flowers bloom, etc.

Anyway, if he's right, the scale of energy available to us is simply enormous:
The figure for the whole world is on the order of 100 million exojoules or quads [a quad is one quadrillion BTUs]. This is the part that would be useable. We now use worldwide just over 400 exojoules per year. So you do the math, and you know you've got a very big source of energy.


How much of that massive resource base could we usefully extract? Imagine that only a fraction of a percent comes out. It's still big. A tenth of a percent is 100,000 quads. You have access to a tremendous amount of stored energy. And assessment studies have shown that this is thousands of times in excess of the amount of energy we consume per-year in the country. The trick is to get it out of the ground economically and efficiently and to do it in an environmentally sustainable manner. That's what a lot of the field efforts have focused on.
No word anywhere on what the projected costs would be, but I can't help but think these plants would have some of the cost characteristics of a nuclear plant - high initial investment, lower operating costs. This might mean the best way to build these plants would be with public financing (again, assuming it works at all.)

Still doesn't help us with liquid fuels, though.

UPDATE: Well, looking through this PDF I'm seeing a few problems. (Note, the PDF is from 1994 and may not reflect Tester's more recent work.) The biggie is that the plant life Tester cites is only 20 years, which is a pretty short life span for a major investment like that. Secondly, the price per kwh is pretty high, even by today's standards. Thirdly, the vast majority of the "energy" released by this plant is heat, which the document assumes would be sold on to a district heating grid. The problem is that most of the world isn't Denmark, and doesn't have a well-developed cogeneration grid.

But that first problem - the 20 year lifespan - seems really problematic to me. Another article by Tester (here, PDF) states that "Typically, within a period of time less than 10 times the production period, essentially complete recovery of original temperatures will occur." So a 20-year lifespan would mean the rock the plant was drawing heat from would take "less than" 200 years to warm back up again, before we could use the area again for generation.

Maybe people will be willing to finance this kind of investment, but I'm not sure I buy it. The lifespan is short (for a generating station) and the costs are still high. If the lifespan issue weren't an issue of physics, maybe I could see a work-around, but until then color me unimpressed.

2 comments:

someone said...

Personally I am a little doubtful of the future of any source of power that still uses heat as a source of energy. Clean Coal has expensive scrubbers. Fission requires a complex reactor and has waste disposal costs. Geothermal requires maintaining a pipe leading to the center of the earth, and equipment which can handle such a crude source of heat with mineral deposits and other unwanted material mixed in. Fusion requires an expensive containment field, and a heat engine which can handle hot plasma without vaporizing. Solar thermal requires concentrating a very diffuse source of power, which is only available intermittently, The fact is all rely on sources of heat which can not be harnessed easily (unlike say natural gas), meaning that cost is determined by factors like raw materials and construction. To build any of these plants, requires steel or concrete and working mechanical parts. All of these are expensive, but are all for the most part, a necessary expense. Conversely, using photovoltaics and to a lesser extent wind, it is just a matter of finding better ways to make them.

I would like to add however, that while the above mentioned sources make poor sources of power, in the long run, compared to solar. Many could still be used as sources of industrial or residential heat.

Gar Lipow said...

Solar thermal is solar. And the issue with variablility applies to PV as well. The advantages of solar thermal over PV at the moment is two fold:

A) one third cheaper

B) High temperature heat can be stored via molten salts much less expensively than we can store electricity.

Should expected breakthroughs occured, both these could change as PV and electricity storage both drop in price. There are various types of public investments that could make it occur sooner. But lots of things people expect to happen in six months time end up NOT having happened decades later. Because of not knowing when we will get inexpensive PV or inexpensive electricity storage, I'd suggest that solar thermal electricity has to be part of the renewable mix.