[domenad]

I have never understood how Geothermal energy works. Theoretically, a very hot earth core would radiate heat outward until temperature throughout the crust equalized. What produces the heat? If you drain the core of heat, how is it replenished?

[thackney]

Think about emptying the ocean using a thimble.

You are depleting it, but not measurably.

[RightWhale]

The earth is still giving off more heat than it gets from the sun. The core won't be cooled off much by thermal mining. It should be good at least as long as the sun itself, that is, another 500 million years.

[Fudd]

Theoretically, a very hot earth core would radiate heat outward until temperature throughout the crust equalized.

I am not a geologist, so take this with a grain of salt.

Yes, the earth is cooling down, However, the process is cosmically slow, and delayed by mitigating factors such as the decay of radiactive elements in the crust and tidal convection from the Moon's gravitational field. If we had a smaller planet (that cools faster) without a significant moon, our planet would be a cold, lifeless rock (like Mars).

[js1138]

If you drain the core of heat, how is it replenished?

Radioactive decay. This has been understood for nearly a hundred years.

[Species8472]

The average geothermal gradient of the earth is 25°C/km in depth. This means that anywhere that you drill on earth over 4000 meters depth the temperature is above the boiling point of water. You drill to the proper depth, pump water down and collect the steam and recover energy from the heat.

[Gorjus]

What produces the heat? If you drain the core of heat, how is it replenished?

The heat is actually caused by - as the article says - "naturally occurring" radioactive materials. Basically, it's an underground nuclear reactor used to heat water to make steam.

And you don't replenish it, but you probably don't have to worry about depleting it, either, since you're not really changing the amount of radioactive decay, just taking advantage of it.

The problem is money. The 'expert' makes light of the fact that there are a few engineering issues to resolve, and I don't doubt the technology is there to do what he wants. But the cost of establishing and maintaining the reservoirs (and the pumping, etc.) is not small. Would this be economically competitive with above-ground nuclear reactors to provide the same heat? I'd like to see the numbers.

Of course, we're nationally stupid on nuclear reactors - paranoid far beyond any rational risk assessment. So on one hand, you might think it would be easier to use a naturally occuring underground nuclear reactor instead. But the first time there's a tiny little earthquake somewhere that someone blames on the drilling, or the pressure, or whatever . . .

It's not clear to me that the socialists who live for the power of restricting other people's choices will ever allow such a 'risky scheme.'

[Publius6961]

I have never understood how Geothermal energy works. Theoretically, a very hot earth core would radiate heat outward until temperature throughout the crust equalized. What produces the heat? If you drain the core of heat, how is it replenished?

Its a nuclear reaction, pretty much self-sustaining and on a the human scale, limitless. But.

This guy is flat out dishonest.
Yes, the heat is there and it's almost limitless but...

He completely ignores the problems associated with its extraction, which have not been solved. I have lived all my life in the area close to the guysers, and the production has been scaled back dramatically since the trial began 30-40 years ago.

The problem is similar to oil shale extraction. The process is easy enough. Dealing with the byproducts is not.
Heavy concentrations of minerals in the process render all the equipment useless in a very short time. Treating the mineral deposits and neutralizing them renders the resulting energy uneconomical; when factoring in the total cost of extraction, it is still economically not viable today.

The problem is analagous to the ICC building at Georgetown University, with a gigantic roof covered with solar cells which had great promise. Until the cost of maintenance and keeping the cells clean for peak efficiency was factored in. It is now just a feel-good white elephant.

There is a fundamental dishonesty with subsidized energy production.

[ko_kyi]

Consider that a very large object like earth has a huge volume compared to surface area - as explained by this page:

http://www.tiem.utk.edu/~gross/bioed/bealsmodules/area_volume.html

Since heat can only escape via the surface, most of the heat generated by radioactive decay is trapped inside.

You couldn't drain the core of heat no matter how you tried - The huge amounts of heat we could drill to are a mere onion skin on the earth.

[Michael.SF.]

One company, Ormat an Israeli company with offices in Reno, Nevada, has some information on Geothermal. They are one of the world's leaders in the designing and construction of these type of plants. To give you an idea of what is required, here is a picture of one small plant:

In the middle of that small picture is a double shafted motor or generator, probably about 700-1000 HP, connected to what are either a pump and a turbine or possibly two turbines. That equipment represents well over a million in capitol costs alone.

[norwaypinesavage]

The heat is produced by radioactivity within the earth. It's a small amount of radioactivity per cubic inch of interior, but there are a whole lot of cubic inches of material within the earth. The outer layer of the earth acts like a super insulator. The "R" value of the earth is not too good. It's only about R=1 per inch of thickness, compared with R=3 or 4 per inch for a good ceiling insulation. However, again, there are a whole lot of inches of insulation in several miles thickness of earth surface layers. So, the heat from the radioactivity is contained within the earth because of this very thick insulation layer on the surface. The amount of heat generated is large compared with the mount that would be used up with any geothermal devices, so it should last indefinitely.

[Lunatic Fringe]

Radiation, pressure, and friction.

[MainFrame65]

Internal heating within the Earth comes from the gravity compression from formation of the planet plus radioactive decay of Potassium, Uranium, and Thorium. It will continue for many millenia. More info here: http://www.sciencedaily.com/releases/2003/12/031215072752.htm

[TASMANIANRED]

Dirt is a wonderful insulator..

[3niner]

I have never understood how Geothermal energy works. Theoretically, a very hot earth core would radiate heat outward until temperature throughout the crust equalized.

"Theoretically" yes, but it will take many billions of years for that to occur, because the Earth's crust is a poor conductor of heat (very good insulator). Also, more heat is being generated from radioactive decay.

What produces the heat?

The original heat came from the condensation of the interstellar dust cloud which formed the Earth. As it gave up its gravitational potential energy, the Earth became a very hot lump of molten rock. In the last several billion years, the surface has cooled to the point where there is a skin covering what is still mostly a molten planet.

There are also radioactive elements distributed throughout the mass of the Earth. As they decay, they give off tiny amounts of heat. This might seem insignificant, but there is a lot of planet containing these elements, and it takes a very long time for the heat to reach the surface and radiate into space.

If you drain the core of heat, how is it replenished?

Even in our wildest dreams, we could only tap a tiny fraction of this energy. We will not drain the core of heat. Also, to some extent the heat is being replenished through radioactive decay.

[dr huer]

When gravity assembled the earth from stone and iron, the gravitational potential energy of the uniting parts was converted into heat, and the top rock layers keep this fossil heat contained. Furthermore long lived radioisotopes contribute.

[KSCITYBOY]

pressure