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A winning solution for renewable energy and CO2 reduction?


June 9, 2011

Two scientists are proposing the use of high-pressure carbon dioxide, instead of water, for extracting geothermal heat from the Earth

Two scientists are proposing the use of high-pressure carbon dioxide, instead of water, for extracting geothermal heat from the Earth

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A promising new innovation in geothermal technology, that offers a novel solution to climate change, has been created by two researchers from the University of Minnesota's Department of Earth Sciences. The technology focuses on tapping heat from beneath the Earth's surface. By using high-pressure carbon dioxide (CO2) instead of water to extract the heat, the system has the potential to produce significantly more efficient renewable energy. At the same time, by sequestering CO2 deep underground, it actively reduces atmospheric CO2. It's being hailed as a two in one solution for climate change.

The approach, coined the CO2-plume geothermal system (or CPG) was discovered by Earth sciences faculty member Martin Saar and graduate student Jimmy Randolph, in the University of Minnesota's College of Science and Engineering. They first struck the idea in 2008 whilst driving to northern Minnesota together to conduct unrelated field research on geothermal energy capture and geologic CO2 sequestration.

"We connected the dots and said, 'Wait a minute - what are the consequences if you use geothermally heated CO2?'" recalled Saar. "We had a hunch in the car that there should be lots of advantages to doing that." They submitted their idea to the University of Minnesota Institute on the Environment's Initiative for Renewable Energy and the Environment (IREE), and were given a US$600,000 grant to further develop their concept.

The core innovation at the heart of the CPG model lies in the use of high pressure CO2 instead of water. Established conventional approaches for transforming the Earth's heat into electricity involve extracting hot water from rock formations several hundred feet below the Earth's surface at key hot spots around the world. The CPG system takes this a step further by using high-pressure CO2 instead of water as the underground heat-carrying fluid. As CO2 travels more easily than water through porous rock, the heat can be extracted more readily, making it a more economically and technologically efficient system than traditional geothermal electricity production.

Further promising benefits of the CPG system include the fact that pure CO2 is less likely than water to dissolve the material around it, thereby minimising the risk of "short-circuiting" or blockages that occur in water-based geothermal systems. Generating geothermal power with CO2 instead of water would also be particularly beneficial in regions where water is scarce. Saar and Randolph also believe the CPG technology could be used in parallel, to boost fossil fuel production by pushing natural gas or oil from partially depleted reservoirs as CO2 is injected. Perhaps the biggest attraction of the CPG system is its promise of creating "clean" renewable energy. By sequestering CO2 deep underground, it is prevented from rising into the atmosphere.

Saar and Randolph are now planning to move the CPG into the pilot phase. The two have applied for a patent, and plan to form a start-up company to commercialize the new technology. The initial simulation results of the CPG suggest they could be onto something potentially groundbreaking.

About the Author
Bridget Borgobello Bridget is an experienced freelance writer, presenter and performer with a keen eye for innovative design and a passion for green technology. Australian born, Bridget currently resides in Rome and when not scribbling for Gizmag, she spends her time developing new web series content and independent cinema. All articles by Bridget Borgobello

Using C02? I heard it\'s a poison gas that has suddenly appeared in the last 30 years due to excessive capitalism. Have there been any studies proving that C02 is safe if humans are exposed to it? What if there were an accidental release due to scientists suddenly exhaling over this power source?

I thought we were supposed to not use any energy at all, because the energy resulting from excess Eco-Sanctimony could recharge our pedal quad-cycles and dry out our wet messenger bags.

How fortunate that we were saved from nuclear power with its vast, clean, cheap power and efficiency. The Japan disaster showed us that the world almost ended when all 3 Series-1 reactors melted down completely.

OK, so nobody died. Or was even injured. But maybe somebody might - Let\'s hope so.

Todd Dunning

Todd strikes again with another remarkable observation. In one comment you criticise the pedal quad-cycle for being \"low tech\" to the point of comparing it to the Amish mindset and in this one you remark this new innovation is somehow a step backward.

Essentially, if I get it right, you want the world to go 100% nuclear without bothering to research or experiment with any other form of power generation, because that is what Todd the Almighty has decreed? Good one. The disaster in Japan has shown us that nuclear, like all methods of mass power generation, is subject to disaster. It has also shown that leaking nuclear waste into the ocean and surrounding landscape is undesirable in the same way that a massive coal fire (from a failed coal plant / mine fire) spewing tons of toxic particles into the air is undesirable.

Pushing C02 underground to be heated so it can spin turbines instead of steam is more efficient (or so these guys are saying, I wouldn\'t know as I\'m not doing the research) than using water. Water is something we want to drink, C02 is something we make lots of very easily. Seems like a win-win to me.


I have done some research on this topic about 2 years ago and it seems these guys get about the same conclusion. As Todd and Scion indicate, it is always suspect to disasters. And yes, there have been accidents with CO2 in the past.

The main danger of CO2 is when it is release in large quantities as it is heavier than air, thus pushing the air away, suffocating people who are unfortunate to be in the wrong place at the wrong time. The largest registered incident was at Lake Nyos on Cameroon, where 1700 people died. The big difference here is that Lake Nyos had a naturally created CO2 \"field\" some tens of meters below the surface, while in my research I used empty gas fields which are located in ranges of 500 to 2000 meters below the ground and are topped by an impermeable layer. This significantly reduces the chances of large scale leaking. Also, this technique makes it easily to detect leaks in an early stage.

Is it dangerous then? Not really. Off course, if it goes wrong badly, people may die. However, using decent safety precautions should reduce the risk to a more than acceptable level.

Dave Janse

Isn\'t this just another way to frack our way out of the kettle into the fire? Extracting CO2 from the air requires energy (a lot, I imagine) and so does injecting it. Yeh, it probably saves some of our increasingly hard to find potable water, but if fracking gives us explosive tap water, won\'t carbon injection make it all carbonated? Don\'t we raise hell with Coke and Pepsi for \'polluting\' our drinking water in just that way? Whatever happened to powering individual homes and businesses at that location with solar and wind? Imagine the copper wiring, powerline corridors and tax-free rights of way we could get rid of. And just as important, imagine the better national security we\'d have if our power grids were decentralized/self contained and less vulnerable to cyber attack (which is now being thought of as an act of war). And individual power sources diminish the effect of heat waves (such as Detroit is having this early in the year) by providing each home with its own cooling/life saving resources. Nevermind. It is probably too late for any of that now. I started 30 years ago and have been shouting into the (wasted) wind ever since. I am glad to see people working on these things. Maybe some of the knowledge will still be around when civilization rises again.


Scion, read what Dave says. That darn reality stuff really dissappoints the unicorns.

Todd Dunning

This article seems a bit off. Or the idea does. Or maybe me.

Let me get this right: these fellahs want to pump (liquid?) CO2 deep into the earth. It gets really hot. Comes helling back, runs a turbine, we gets the \'lectricity. And the CO2 is sequestered somehow? And the CO2 is garnered from the atmosphere, which involves compression, cooling and distillation. In it\'s self that process takes quite a bit of energy, but it\'s less expensive, somehow, than using water. This whole concept doesn\'t make much sense to me. But someone gave them 600 grand to develop this idea?!

I don\'t understand what the hell the article is going on about. Someone help me (a simpleton) out, would you?


I am all for cost effective clean energy, and scrubbers to remove real pollutants on smokestacks. (This does not mean CO2) If using liquidized CO2 instead of water make geothermal power more cost effective good. But AGW is a greater fraud than Piltdown Man.


Aren't any the technological barriers to the implementation of idea. However, can shouting "Bravo" would be possibly after that as, we will prove the long-termed Safety of such technology. Dave Janse said «... The big difference here is that Lake Nyos had a naturally created CO2" field "some tens of meters below the surface ...». Which a surface mentiones by Dave Janse : a surface between a lake and a atmosphere, or a surface between a lake and a porous sediment stratum under the lake's bottom ? In http://www.nyos.lv/uploads/3420/copy_of_article_new_translation__result.pdf shown that «... Limnological catastrophes on lake" MONOUN "in 1984 and on lake "NYOS" in 1986, were caused by the instantaneous ejections of the gaseous carbon dioxide from the sediment stratums under the lake's bottom .... ». Ie, a natural instantaneous ejections of the gaseous CO2 occurred in the "field", which located in the hard porous sediment stratums at some tens of meters below the the lake's bottom. Consequently, there is not a big difference, about which mentioned by Dave Janse. Concerning "... impermeable layer... ". Absolutely impermeable layers do not exist. In http://www.nyos.lv/en/krugi-na-poljah/fizika-steblevogo--poleganija-rastenij-v-krugah-na-poljah-30643 shown that Instant rupture porous rock is accompanied by instantaneous creation the cavity a crack and the gas-permeable network, consisting of great number of the micro-canals and the micro-passages. Such process of creation of gas-permeable network has possibility overcome impenetrability layers, which are traditionally considered impenetrable.


There is no such thing as liquid carbon dioxide. It is either a gas or a frozen solid. So pressurized gas is used. Lake Nyos had underground volcanic activity, which released the gas from the lake bed. The surrounding landscape formed a bowl, and as CO2 is heavier than air, it displaced the oxygen, and suffocated all life silently, and with no warning. As far as this geothermal setup goes, C02 is pumped down ,and back up in a circuit. I don\'t see how any can be sequestered, but that is not the main aim of the project. When water is used, it is cool when it goes down, is heated by the the rock, which creates pressurised steam.


windykites1--- Thy knowledge is lacking.

From Wikipedia:Carbon dioxide Liquid carbon dioxide forms only at pressures above 5.1 atm; the triple point of carbon dioxide is about 518 kPa at %u221256.6 °C (see phase diagram, above). The critical point is 7.38 MPa at 31.1 °C.[8]


Liquid CO2 is easy to obtain, as well as supercritical CO2(a phase where there a hardly differences between gas and liquid, a sort of gaslike liquid). The critical point Slowburn mentions is correct.

7,38 MPa, or 73,8 bar, is obtained at a depth of about 750 meters. Using a \'normal\' geothermal gradient(so no hot spots), you get a thermal increase of about 30C per kilometer. Based on 10C surface temperature, this requires about 700 meters. \'Regular\' geothermal power plants use depths of about 5 kilometers.

And yes, as Georg mentions, there are always technological barriers. But that\'s why they got additional funds, to overcome those barriers. Safety is important, and I agree nothing exists in the soil which is true impermeable. But it gets close enough to being impermeable. If holes appear in the layer, people will notice. It is easy enough to detect CO2, even if there are only minor leakages. Also, you state that this technology is not so different from Lake Nyos. Check Table 1 on page 15 of the article you posted. There is a distance of 280 meters from the surface to the aquifer, including a 209 meter lake, a 10 meter layer and about 61 meter soil. Only 71 meters of soil compared to the deep underground stated in this article. Since supercritical CO2 is best suited for geothermal purposes, based on its ability to travel through porous media, you have difference of at least a factor 10 in depth.

For Yodecat, it seems you got it right by a fair bit. CO2 gets pumped into the soil, gets heated up, comes back to the surface, runs a turbine and goes back into the soil. The main mistake made with this idea is that it seems like it costs more energy than it would cost, based on the pumping and compression. However, the energy source is the heat in the earth, which provides more energy than the cycle takes. However, I doubt they would take it from the air, since that is a costly process and it is much easier to capture CO2 at exhausts from industry.

Dave Janse

Dave Janse, I respect your opinion. However, safety is more important. Instantaneous creation the gas-permeable network in the impermeable soil creates instantaneous outburst of gas into the atmosphere. Such instantaneous outburst of gas does not apply to the category of «minor leakages» When takes place the instantaneous outburst of gas, you haven\'t time for notification of people and for rescue of people . On such scheme takes place outburst of methane in coal mines. In Table 1 on page 15 it is said «Distance, along the vertical line, from surface of the lake till the pressure zone of the pressure confined aquifer, m . 280.34. \" ( http://www.nyos.lv/uploads/3420/copy_of_article_new_translation__result.pdf ) . Hence the explosion occurred at a depth of 280 m from a terrene . Explosion occurred under Lake Nyos because at this place the pressure of overlying layers (including water\'s mass of the lake) was minimal. No obstacles for such an explosion at a greater depth from a terrene. Before implementing a new technology, it is necessary comprehensively to ground its safety.

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