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EGS, an incredibly promising form of geothermal, involves drilling down to "basement rock", the hot outer layer of the crust, and pumping water down into it to produce steam. Just a tiny percentage of the underground heat capacity of the U.S. could power the nation thousands of times over.  (Source: AltaRock)
New energy source could offer 2,500 times nation's power needs, according to MIT

The world of alternative energy is a confusing one filled with choices.  There's nuclear, solar, wind, and biofuels (such as algae).  Each technology has its own unique advantages and disadvantages.

One technology that's too often forgotten in the mix is geothermal energy.  With interest in alternative energy at an all-time high, the geothermal energy business is seeing a rebirth.  From harnessing volcanic steam deposits to prospecting America's many geothermal sites, many promising projects are currently underway.

Perhaps the most promising source of geothermal is a brand new method called Enhanced Geothermal Systems (EGS).  Where traditional geothermal involves finding naturally occurring steam pockets in the hot layers of rock beneath the Earth's crust, EGS skips the troublesome prospect and makes its own steam, by drilling down the hot rock, cracking it, and then pumping water into the cracks to form steam.  The result -- instant power virtually anywhere in the country.

According to MIT, just 2 percent of the heat between 3 and 10 kilometers beneath the crust of the Earth in the continental U.S. contains enough energy to produce 2,500 the amount of power our country produces yearly.  Literally, just EGS power from the U.S. could power the world.  And these depths are all within the reach of current drilling equipment.

Google is very impressed by the promise of EGS.  Google has decided to invest $10.25M USD to help startups develop the technology as part of its philanthropic arm Google.org's initiatives, which aim to produce alternative energy power at rates cheaper than coal.  The Google investment will not only cover the continuing development and deployment of the technology itself, but also the development EGS information tools, advanced geothermal resource mapping, and promotion of geothermal public policy on a government level.

Dan Reicher, Director of Climate and Energy Initiatives for Google.org states, "EGS could be the 'killer app' of the energy world. It has the potential to deliver vast quantities of power 24/7 and be captured nearly anywhere on the planet. And it would be a perfect complement to intermittent sources like solar and wind."

The latest Google funding for EGS goes to two companies and a university.  AltaRock Energy, Inc. is one of the recipients and will receive $6.25M USD to help it actualize its EGS vision.  The second investment of $4M USD goes to Potter Drilling, Inc., which is exploring new methods of drilling cheaper and techniques for drilling into deep, hard rock, a technology critical to EGS.  Finally Google will deliver a grant of $489,521 to Southern Methodist University Geothermal Lab to aid it in its projects of updating geothermal maps of America.

Dr. Larry Brilliant, executive director of Google.org also delivered praise for the new direction.  He states, "Innovation is the path to massive quantities of cleaner, cheaper energy. The people we're funding today have a real shot at lowering the cost of EGS, and bringing us closer to our goal of Renewable Energy Cheaper than Coal."

Mr. Reicher quickly adds, "EGS is critical to the clean electricity revolution we need to solve the climate crisis, but EGS hasn't received the attention it merits. That's why we're pressing for expanded support from government and increased investment from the private sector.  EGS is critical to the clean electricity revolution we need to solve the climate crisis, but EGS hasn't received the attention it merits. That's why we're pressing for expanded support from government and increased investment from the private sector."



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Fourier's Law...
By Mclendo06 on 8/19/2008 7:44:41 PM , Rating: 2
I haven't done any calculations to this effect, but I do want to voice one question/concern.

Is there a possibility that the water being pumped into the ground will cool the rock around it sufficiently that it would stop producing steam, or is the thermal conductivity of rock high enough that the region around the cool water being pumped in would be quickly driven back towards equilibrium? Basically, how much power could be drawn from a single point in the ground without cooling the rocks too much?

Just to compare a few numbers, the thermal conductivity of rock at water-boiling temperature appears to sit in the range of 2 ~ 4 W/(m K) (based on http://www.agu.org/reference/rock/10_clauser.pdf , look at P. 111) whereas for copper in the same temperature range, this value is 390 ~ 380 W/(m K). It just seems that heat would have a hard time flowing to the steam-generation region of the rock, meaning that the power that could be taken from a particular drill hole would be rather limited. If anyone would care to solve the 1D differential equation required to determine how much power could be extracted from a point (or small sphere if you must resort to numerics) surrounded by an infinite region of matter with gamma = 4 W/(m K) and ambient temperature of 500 C (this is probably a little generous and would be a best case scenario based on what I can tell about temperatures at that depth) I would be most interested in the answer. Figure water for the working fluid if you want to get into some tricky thermodynamics. I'm just too lazy to dig around for the solution to this problem right now.




RE: Fourier's Law...
By Mclendo06 on 8/19/2008 8:12:03 PM , Rating: 2
Okay, I decided to go look it up because some rough calculations can be done pretty easily. First, the result:

The energy flux (power) that is extracted from the steam-producing region is about 200 MW in the idealized case outlined below, so I suppose that this could be a viable means of producing energy.

Now for my gross oversimplification:
I assumed the energy-extraction region is a sphere with a 1 m radius and the ambient temperature is 500 C an infinite distance out. The worst assumption I made is that the temperature at the wall of the inner sphere is constrained to 100 C - meaning I assume that heat gets into the water way too efficiently (ignoring flux) and that the absolute maximum amount of energy possible is being sucked from this small region. However, even if the actual energy output is 1/20 what my back-of-the-envelope numbers are, you have a hole in the ground producing 10 MW of energy 24/7. Had my numbers said that you will get a few megawatts, I'd have serious doubts, but this seems at least feasible, although likely not nearly as good as my rough numbers above might indicate. Further input welcome...


RE: Fourier's Law...
By Solandri on 8/19/2008 8:51:14 PM , Rating: 3
It's been a while since I read up on this, but I seem to recall your concern being on of the problems. There were some ideas of finding an underground salt deposit, sending water to dissolve the salt and excavate a cavern down there, then using that increased surface area for heat exchange. Or to blast explosives down there to crack the rocks thus increasing the surface area that way.

The temperature of the water is not constrained to 100C. At those depths, the water pressure would be several hundred atmospheres (102 atm per km), raising the boiling point considerably. In fact one of the problems they were coping with was the water flashing into steam en-route to the surface. This would drive the turbine, but it would also push the water column back down. You have to keep the water pressurized until it hits the turbine. If you lose pressure containment, the flash steam could blow apart your piping at depth.

But like I said, it has been a while and my memory may be faulty.


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