A new technology for producing geothermal energy could also be a method for sequestering carbon dioxide beneath the earth's surface, which could make this one of the most carbon-negative methods of producing energy. Geothermal power often has other environmental impacts, which usually puts it in the same category with large-scale hydropower: a source of clean power from a CO2 emissions standpoint, but with other negative environmental impacts. But using CO2 rather than water could make this a very attractive way of generating geothermal power in an even cleaner way.
The test project being carried out in Arizona by Green Fire Energy is working to develop a method of producing geothermal energy based on research by geoscientist Donald Brown at Los Alamos National Lab and further developed by Karsten Preuss and others at Lawrence Berkeley National Lab.
Geothermal power usually requires large volumes of water to be pumped underground to generate steam for power generation. By instead using CO2 as the working fluid, this new method avoids the need for large volumes of water and also serves to sequester some of the CO2 underground as it gets trapped in the process. "[Carbon dioxide] will be tapped, pressurized to a 'supercritical' state and injected underground. When this CO2 returns to the surface, it will cycle through a power conversion system, creating power. After each cycle, the CO2 will be recompressed and reinjected underground. During this process, a portion of the CO2 will be permanently trapped in porous underground rocks. Thus, the process emits no carbon – and may actually store some of it deep underground."
Interestingly, this is not the only technology using CO2 that we've seen recently, and there might be an interesting synergy between the two. This is an especially positive development for the desert Southwest, which has geothermal potential, but little available water with which to exploit it. Sequestering CO2 from nearby coal-fired plants could serve as a source for the CO2 to run this process, as well, which would help further improve the air quality in the region.
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