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117 comments on Low Temperature Geothermal Power
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117 comments on Low Temperature Geothermal Power
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The kalina cycle sure is cool, and 3MW is a nice tidy way to power an out of the way piece of nowhere; But the notion that Geothermal power has anything to offer in terms of energy generation just doesn't hold up to scrutiny; Wind, nuclear, solar all of these are scalable up to the terawatt range. Geothermal... not so much.
Errr - what makes you think that ?
http://peakenergy.blogspot.com/2007/11/geothermia-revisited.html
http://web.mit.edu/newsoffice/2007/geothermal.html
http://www.google.com/corporate/green/energy/faq.html
Care to try to debunk the MIT study ?
TerraWatts would be difficult. But hundreds of GW looks more feasible. Which is still a lot of power. Qualifies as 'significant' in my book. And since it's clean (at least the modern binary plants) and cost effective (Raser has a power purchase agreement for $ 78/MWhe even for a small plant) anything we can get is welcome. If the hydrogen fraction drilling thing works out, a TW might be feasible.
Sorry, I accidently downrated your comment. I had a quick look at the MIT report and it sounds wonderfully encouraging. Thank-you.
What about the rate of heat exhaustion? Will power plants have to relocate to a higher quality site over the heat resource (reserve?) after some decades, centuries, millenia?
Yes. I took a class with Professor Tester, and he explained that the primary issues are flow rate, governed by the permeance of the fractured rock. Where you are mining for heat, you will create a local cool pocket, which will take a long time to regenerate due to natural processes. So, if the area you drill in is made up of very dense non-porous rock, the volume of accessible water around the mine may be limited. He taked about it in terms of a "decades" lifespan for a typical mine, but I would assume that the lifespan would be more than linearly decreased as the power drawn increases.
Thanks for your response. Are there studies comparing the energetic and material costs of construction, maintenance and operation of these power plants with other 'non-polluting' power systems? Any leads?
There was a considerable program on Geothermal in the U.S. back during the last energy crisis. The Hot Dry Rock program got a lot of attention, but there were some significant drawbacks. There were, at the time, lots of reports; I must have dumped at some stage several drawer fulls (Moving offices). Sadly it was before digital records of such things, and the old reports may not be widely available any longer.
mit and google links discuss EGS which stands for Enhanced Geothermal System. Neither article is a refereed technical report. So I cannot determine what makes it 'enhanced' in a technical sense. There is, of course, no existing geothermal energy industry. Only existing geothermal installations. Each installation appears to be uniquely designed for its peculiar location.
Both articles appear to equate 'better' and 'high grade' with higher temperature, so BGs report concerns something out of the box of ordinary thinking. A well known technical problem with geothermal is that the thermal fluid is water. Water is a polar liquid. Hot water has a great capability to desolve naturally occurring minerals, which then flow a short distance in the drill pipe, cool a bit, and deposit out of solution. This clogs the pipe rather quickly. This phenomenon is unknown in petroleum wells, but is a big problem for geothermal wells. Neither article describes or discusses this issue to my satisfaction.
Two short quotations from the mit article:
1) Of particular importance is to demonstrate that EGS technology is scalable and transferable to sites in different geologic settings.
2) The shallow, extra-hot, high-grade deposits in the west should be explored and tested first.
Scalability has not been established. The feasibility of EGS is dependent on local geological conditions. There is no mentioned of how it being enhanced affects its feasibility.
BigGav's new information is about a new idea (new to me, anyway) that deliberately targets low temperature heat. This has the possibility of keeping the wells unplugged longer. It has the down-side that thermodyanmic efficiency is much smaller. But if, in Australia in this artesian basin, they can get EROI that keeps them in business, then good for them.
Sorry - the EGS links were in response to the question of geothermal (in all its manifestations) being able to provide terrawatts of power.
I haven't seen any information on how far low temp geothermal can scale (or at what price points it becomes competitive with other forms of energy).
But the German and Australian experiences and plans show that it could certainly fill a useful niche for providing our future power needs.
Regarding price, Raser gets a $ 78/MWh power purchase agreement. That's just for a small plant (10 MW electrical), perhaps bigger ones will be a tad more cost effective. Even though these systems are modular, large plants should have less overhead costs per MWh.
Do we need centralized power generation ? The power blackout a few years back in Eastern USA/Canada & the Eastern Canadian ice storm demonstrated what happens when the grid is centralized (and improperly maintained). Regional power generation would stop country wide blackouts but would admittedly require more maintenance and not work on economies of scale.
Power also goes down even when the problem is regionalized or localized. To the extent that the individual cannot do without power for any length of time, local backup must be installed.