The Potential of Geothermal Power

EskimoJoe wrote with a link to an AP article about progress in the development of geothermal energy. A Swiss company is competing with another in Australia to be the first to commercially develop a geothermal power plant. The concept is simple to understand: earth's core heat transforms water into steam, which in turn causes a turbine to revolve. The potential, though, is enormous. "Scientists say this geothermal energy, clean, quiet and virtually inexhaustible, could fill the world's annual needs 250,000 times over with nearly zero impact on the climate or the environment. A study released this year by the Massachusetts Institute of Technology said if 40 percent of the heat under the United States could be tapped, it would meet demand 56,000 times over. It said an investment of $800 million to $1 billion could produce more than 100 gigawatts of electricity by 2050, equaling the combined output of all 104 nuclear power plants in the U.S."

Misleading

[Remusti]

The summary is misleading, Geothermal power [wikipedia.org] plants already exist.

The first one?

[BlackPignouf]

http://ww.geothermie.de/iganews/no39/guadeloupe_ge othermal_developmen.htm [geothermie.de]

Huh?

[jawtheshark]

A Swiss company is competing with another in Australia to be the first to commercially develop a geothermal power plant.

I think they should go on a trip to Iceland... Frankly [wikipedia.org]...

The article is 49 years out of date

[Anonymous Coward]

Here in New Zealand we've had geothermal power since 1958..

http://www.ew.govt.nz/enviroinfo/geothermal/energy .htm#Heading2 [ew.govt.nz]

Just 40% They say..

[Yazeran]

Well they may be right that just 40% of the heat flow through the continental shield of the US may meet the energy demand 56k times over, the ticklish part is extracting the energy in an economic way. So far the only places where geothermal energy is usable is near active Volcanic areas where the geothermal gradient is steep enough to allow high temperatures near the surface and thus a high enough energy density to make the investment profitable (Think Iceland and California). All the other places the heat flow is too low to be usable for anything else than house heating.

Another thing one must address is that the heat flow can only be used where permeable strata exists in the ground making it possible to circulate water to extract the heat. In places with crystalline bedrock, the heat flow can not be used.

Yours Yazeran

Plan: to go to Mars one day with a hammer.

Not quite the same....

[Mogster]

but Wairakei here in NZ is a geothermal power generator http://en.wikipedia.org/wiki/Wairakei [wikipedia.org]
It uses the natural geothermal activity local to the region.

Re:Misleading

[blowdart]

Spotty effects? Iceland's geothermal power plants provide 26% of the power there (the majority is from hydroelectric), plus geothermal heating plants heat around 87% of homes. On the other hand the baths and showers I had there did stink of sulphur.

Oldest one is over 100 years old

[Anonymous Coward]

The oldest (over a century) and largest (produces 10% of the world's entire supply of geothermal electricity) is still in Italy, Larderello [wikipedia.org]. It produces more than 500 MWe.

Re:What are the side effects of geothermal?

[vrmlguy]

First off, there are no such things as "stalagtites". There are only stalactites (which hang tight from the ceiling) and stalagmites (which stand mightily on the ground); from your description I presume that you mean the latter. However, both are formed by dripping water, so perhaps you mean the tufa towers of Mono Lake [wikipedia.org]. But those formed underwater and were only exposed when Los Angeles started diverting water from nearby rivers and the lake's water level fell. But no matter what you mean, these projects will only effect a very thin layer of the upper-most magma. You might as well worry about an oil spill effects the ocean's currents.

Shattering rock is how the process words. Water has a hard time passing through solid rock, so the mining process initially injects cold water to form microscopic cracks in the rock for the water to flow through. In the Swiss project, the earthquakes occurred because they were injecting water into a fault, in effect lubricating things enough that the two sides of the fault line could side easier. This may be a show stopper for that project. In North America, we will probably want to avoid drilling along the Pacific Coast or anywhere near the Reelfoot Rift [wikipedia.org].

Lastly, Earth's magnetosphere is produced by its core, not the magma. And if "sucking the heat out" could cause volcanoes to "dry up", I think that most people would consider that an additional benefit, not a disadvantage.

Re:article (or quote) must be wrong

[gEvil (beta)]

No doubt. And you can see this on NYTimes.com; I emailed them. How long do you think they will take to correct this?

Why would they correct something that they didn't get wrong? Just because a few slashdotters don't feel that the number cited is correct, you're going to tell them that they're wrong? How about doing three minutes of research to find out for yourself first? Let's hear it for "Citizen Journalism", where truthiness is more important than facts.

And for those of you playing at home, the relevent passage from the MIT study (press release here) [mit.edu] (actual study here) [inel.gov] [PDF warning] is this:
Based on growing markets in the United States for clean, base-load capacity, the panel thinks that with a combined public/private investment of about $800 million to $1 billion over a 15-year period, EGS technology could be deployed commercially on a timescale that would produce more than 100,000 MWe or 100 GWe of new capacity by 2050. This amount is approximately equivalent to the total R&D investment made in the past 30 years to EGS internationally, which is still less than the cost of a single, new-generation, clean-coal power plant.

Re:The numbers

[Solandri]

"A so-called hot rock well three miles deep in the United States would cost $7 million to $8 million, according to the MIT study. The average cost of drilling an oil well in the U.S. in 2004 was $1.44 million, according to the U.S. Energy Information Administration."

Yea, so that's about six times more expensive. But wouldn't the savings be much more in the long run? And more "environmentally friendly"?

Oil wells in the U.S. are incredibly non-productive. People always think of oil wells as the geysers they see in movies and cartoons (or Kuwait during the first Gulf War). The reality in the U.S. is that two-thirds of them produce fewer than 5 barrels of oil a day [doe.gov]. In fact, only about 1.5% of them produce more than 100 barrels per day. The average for the nation is 13.7 barrels per day per oil well.

At a crude oil price of $75/bbl, a 13.7 bbl/day well is yielding $1027.50 of product per day, or $375,284 per year. At a cost of $1.44 million, it takes the well 3.84 years to pay for itself. At a cost of $7-$8 million, it would take 19-21 years to pay for itself. That's assuming you could extract as much energy-dollars from a hot rock well as from an oil well (can't find any numbers on this, but it can't be much higher or the oil companies would be all over this since they're already in the best position to take over any market involving drilling).

The hot rock well does have the advantage of being guaranteed productive for those 20 years, but you're talking "long term" as in way past the term of any elected official. It's hard to get them to pay for needed maintenance on roads and bridges, much less make an investment which won't pay for itself for 20+ years.

Re:Misleading

[krilli]

Hi, I live in Iceland.

We use hot water pumped directly from shallow wells for the hot tap water. It contains sulfur.

It's close to 100C, so you can use a heat transformer to warm up the non-sulfuric cold water for showers, etc. Some houses here do.

Re:Misleading

[ozmanjusri]

Go look up the Carnot engine.

Um no. Thanks for the patronising suggestion, but I'm already familiar with the Carnot cycle.

I'd suggest you look up the Kalina cycle, since it's the one that's relevant here.

Re:Misleading

[Xemu]

As for African cultures, the majority of the Sahara desert became so because of goats, which were protected from predators by humans.

Wow, that's so misinformed I can only laugh. Do you have any idea on how many goats that would take?

Sahara, for example, was born 4000 years ago because of a climate change. Land use by man was not an important factor in the creation of the Sahara. http://news.bbc.co.uk/1/hi/sci/tech/390097.stm [bbc.co.uk]

Re:The question of scale

[Anonymous Coward]

Your premise is sound but the *rate* must play some part..

If you lower the temperature in a region, heat flow in the region goes up. Period.
Flow being determined from the difference in temperature * area * thermal conductivity.

This is being *conducted*, not radiated.. because it is a solid/semi solid depending
on pressure and temperature. We can probably eliminate convection as a concern, too.

It is still a small amount in geological terms.

Re:Misleading

[wytcld]

The American indians simply lacked the technology to have a significant impact on their environment until they got horses, at which point their population expanded and they routinely exhausted hunting grounds,

You're good at making things up. At the same time the Native Americans got horses they also got European diseases, which by current best estimates wiped out at least 50%, perhaps as much as 90%, of their pre-contact population. But before they got horses, they'd had widespread effects on their environment. For example the wonderful scenery at Yosemite that whites think of as "unspoiled" entirely depended on the fires Native Americans methodically set to clear off forest and produce the grasslands that game animals thrived on. They weren't destroying nature with those fires, but they were certainly maintaining nature in a different balance that it would have been without their efforts - a balance more fruitful for their own uses of nature. Then Muir convinced us that this was "virgin" wilderness, and we removed the natives.

The difference between Native American and white approaches to nature is that Native Americans tuned nature to be even more beautiful for human thriving, while the typical white approach is to "conquer" it. This attitude the whites brought from Europe, where the wilderness was largely identified with evils and dangers, rather than a thing of beauty to be appreciated for its potential to nurture us. That European attitude finally changed - in part because the American landscape changed us (see the New England Transcendentalists), and word got back to Europe from here; in part because the English Romantics discovered their own landscape, and then expanded from there to the world. But most of Europe viewed nature like the French, for whom it belonged best in geometric gardens, or the Germans, for whom the woods were fully of mythic monsters and deadly dangers.

Oh, please.

[hey!]

Of course I did look up the Kalina cycle before my post, both technical descriptions of the process and descriptions of proposed projects.

Nobody is claiming this process is 100% efficient. They're talking about efficiencies in the range of 60%. In some cases proponents talk about efficiencies that are "80% higher". However since existing coal plants reach efficiencies of over 30%; adding 80% to that gives you 110%; so they must be talking about current efficiency *1.8, not current efficiency + 80%. That would yield efficiencies in the range of 55% to 65%, precisely what the proponents have been claiming when they talk in absolute terms.

It's misleading to say these things run off of "waste heat", as if "waste heat" is something different than "useful heat". Heat is heat; and while more efficient processes do capture some heat that would otherwise be wasted, but they never capture 100%. It's physically impossible.

If you actually look at a block diagram a Kalina cycle engine, you will see it has an element called a condenser. In it, cold water enters, and "cold" water exits. But if the water were perfectly "cool", why have a condenser at all? Or if it were needed to work some magic, why not feed the output of the condenser back into the input?

The answer is that the "cold water" exiting the condenser may be relatively cold compared to the liquid in the main loop, but it's still warmer than when it entered the condenser. If you fed the "cold water" output of the condenser back into the input, the system would stop functioning. The system won't function unless there is something to carry at least a bit of waste heat away.

Why? Simple. The turbine is not 100% efficient. The fluid in the primary loop is chosen to allow a very efficent turbine, but a 100% effient turbine would have fluid exiting at absolute zero. A realistic turbine will have fluid leaving at something above the ambient temperature. Keep running the fluid through the primary circuit, and eventually it becomes as hot as your heat source. Since you can't get heat to flow from hot to hotter, you can't extract any more energy. The temperature on both ends of the turbine is equalized, and it stops turning.

So, the whole shooting match requires enough heat to be extracted and thrown away to return the liquid in the primary loop to some base temperature that is cooler than your heat source. Maybe you can find some use for that waste heat, like heating an apartment block, but you can't utilize that heat within your engine itself.

Remember "The Core"?

[Chmcginn]

No, not the part about the burrowing ship & the nukes and everything. If we actually managed to make a noticeable difference in the outer core/mantle temperature, it would weaken the Earth's magnetic field.

That being said, Earth is about 6E24 kg. The specific heat of silica & iron (the two most common minerals) is .7 & .45 J/gk - average it to .55. That would mean 3E24 J for a 1 degree drop. 3600J is a watt-hour... so 2.1E19 J is a terawatt-year. That means it would take about 140,000 years of 1TW 'drain' to cool the entire (interior of) earth about 1 degree. Even assuming that all human electricity was generated via geothermal energy, it would take somewhere in range of millions of years.

So, yeah, I wouldn't really worry about it.

Re:Misleading

[Ian Alanai]

IIRC American Indians, many African cultures, and even our old agricultural society were much respectful of the environment.

Bullshit. The American indians simply lacked the technology to have a significant impact on their environment until they got horses, at which

Quoted for irony, because horses were native to North America, until the ancestors of the original Americans ate them all.

PS: The pueblo Indians managed to deforest their environment to the point that their culture collapsed.
PPS: Also there is no such thing as 'American Indian Culture'. The American continents (like Europe) were diverse places with extremely diverse cultures. Positive racial stereotypes are still racial stereotypes, m'kay?