Geothermal energy

Posted by David Roberts at 8:45 PM on 02 Aug 2006

Read more about: energy | geothermal power

In yesterday's MIT Technology Review there's an interview with Jefferson Tester, who claims that geothermal power is a potential game-changer in the energy world.

Technology Review: How much geothermal energy could be harvested?

Jefferson Tester: 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.

The idea is to break up super-hot rock way down in the earth, flood it with water that absorbs the heat, and bring the water back up, in effect mining the heat. Tester says the technology's been successfully demonstrated and we could have commercial-scale plants up and running within 10 to 15 years.

The advantage over other renewables is that geothermal provides steady baseload power:

TR: What are the advantages compared with other renewable sources of energy?

JT: Geothermal has a couple of distinct differences. One, it is very scalable in baseload. Our coal-fired plants produce electricity 24 hours a day, 365 days a year. The nuclear power plants are the same way. Geothermal can meet that, without any need for auxiliary storage or a backup system. Solar would require some sort of storage if you wanted to run it when the sun's not out. And wind can't provide it without any backup at 100 percent reliability, because the typical availability factor of a wind system is about 30 percent or so, whereas the typical availability factor of a geothermal system is about 90 percent or better.

It sounds great, but as always, the proof will be in the pudding.

For more info, see this diary by Devilstower over on dKos. Also, another Kos diarist named Leading Edge Boomer says he's seen a (as yet unpublished) draft of a technical paper Tester's co-written on the subject. "IMHO," he says, "this is A Big Deal."

For story: Geothermal energy
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Power Problem

Besides the large temperature gradient needed for efficient heat extraction (which you can get anywhere if you drill deep enough), and an efficient thermal exchange at those depths (which you might get by fracturing rock), you also need a larger enough heat flux from below than the rate at which you are extracting it.

The typical heat flux towards the earth surface is .06 watts per sq. meter--much smaller than the solar energy flux. To generate 1 MW of power, you would need to collect 100% of the geothermal energy over an area of 6.4 square miles. That's a lot of deep drilling.

Abundant energy does not equal abundant power.

by JoulesBurn at 8:11 AM on 03 Aug 2006

... except, of course, to the extent that it's

nonrenewable power, like OTEC, which mines coolness from the deep sea.

--- G. R. L. Cowan, former hydrogen fan
Boron plus pure oxygen: internal combustion without exhaust

by GRLCowan at 9:46 AM on 03 Aug 2006

Coolness of Deep Sea or Ocean

Why might the coolness of the deep sea not be renewable?

It would seem to me that the cycle of radiant energy associated with the rotation of the earth, day and night, would create heating and cooling which gravity would then order such that the cool would be beneath the warm, provided temperature of water is above 39F

by ffletcher at 10:16 AM on 03 Aug 2006

That sounds plausible

Maybe OTEC is more renewable than I had thought. It moves a large amount of heat downward to net a little, or lose a little, electricity, so I just assumed heavy use of it would soon irreversibly vertically mix the oceans.

--- G. R. L. Cowan, former hydrogen fan
Boron: A Better Energy Carrier than Hydrogen?

by GRLCowan at 12:29 PM on 03 Aug 2006

What goes down...

Sticking stuff underground (especially to get useable stuff up/out) has an obvious attraction.

When I was a kid I wondered why we couldn't just tip all our waste into volcanoes, so the lava would take it to the earth's core, melt it all down and separate it all back into its basic chemical and ores again. Wouldn't that be neat?

But I'm just wondering about the consequences of mucking about with the balance of flowing (virtue of heat that is proposed to be removed?) magma, which by the numbers seems so vast anything we do will be very small, but may still be significant.

As one who thought it a stretch when some laid the Asian tsunami at the door of global warming, I was nonetheless moved to at least wonder a tad by subsequent theories based on the consequences of climate change on the ocean floors, and even sucking vast volumes of oil out of the ground.

How sure are we that our demands won't divert enough energy from down there to up here to not have a consequence?

I guess after nuclear I'm just worried that in our desire for more sources of energy rather than using less, we tend to rush into things that may cause a few new problems down the line. But then I was the one who wondered what sucking the energy out of the wind at coastlines may do for inland climate balances.

Just asking. I'd love to be reassured.

Junkk.com Discover - Share - Create with YOUR ENVIRONMENTAL MATES! Read the `Best of the World Blogs'-listed Junkk Male RE:View

by Junkk Male at 11:33 PM on 03 Aug 2006

Geothermal Pollution

I do not know much about geothermal energy, I have attended a couple conferences on this. Ground heat loss will not damage the Earth, though specific geothermal power sites will not be sustainable as they cool down. The environmental footprint is the dirty caustic sulfuric affluent which is often injected into aquifers. Sulfur makes geothermal energy stinks like rotten eggs.

Deep hot geothermal wells are not cost effective. I have been asked about the prospects of increasing shallow geothermal temperatures with solar concentrators because the low grade heat from the ground is not efficient for generating electricity.

Geothermal energy has a niche for carbon-free energy and is one example why wind is just part of what needs to be done.

Most important is that the US has over-developed energy and more energy is not needed. We could shut down 50% of our energy supply with conservation and efficiency improvements, a cleaner and more cost effective base-load source of energy.

by sunflower at 7:19 AM on 04 Aug 2006

Geothermal is here, now, economical

In the real world geothermal is already generating more power than wind and solar combined. Ormat is a $1.4 billion company completely dedicated to geothermal power generation. They already have 900 MW of generation and are consistantly profitable selling power at prices competitive with clean coal (about 6 cents per kwh)
Most of their plants are in geothermal areas but improved drilling thecniques may soon make geothermal economical throughout the world.

http://www.renewableenergyaccess.com/rea/news/story?id=47 ...

by tblakeslee at 3:17 PM on 16 Feb 2007
[ Parent ]

Power Problem

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