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.
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