CO2 pumped deep underground could make geothermal energy projects more efficient

Washington, December 30 (ANI): Scientists have proposed that carbon dioxide (CO2) pumped deep underground for storage could be used to make geothermal energy projects more efficient.

According to a report in Discovery News, this combined system could double the efficiency of geothermal energy capture, while also making carbon storage projects more feasible.

"I think it's really exciting because one of the big problems with most geothermal energy and carbon capture and sequestration seems to be that the economics of either doesn't quite work unless there's some sort of subsidy on the geothermal side, or some tax on carbon on the carbon capture and sequestration side," said Grant Ferguson of St. Francis Xavier University in Antigonish, Nova Scotia.

Typical geothermal energy systems pump water deep underground in geologic hot spots.

The water soaks up heat emanating from Earth's core and brings it back to the surface. The hot water is then used to generate electricity.

However, it turns out that high-pressure, high-temperature carbon dioxide is a more efficient fluid than water for capturing heat from geothermal systems.

Martin Saar and Jimmy Randolph of the University of Minnesota, Twin Cities, proposed that sites where CO2 will be sequestered deep underground could do double duty as geothermal energy production projects by bringing a small fraction of the high-pressure CO2 back to the surface and using it like hot water to generate electricity.

The CO2 would be pumped back down after the heat was extracted.

"Now, we have this approach using CO2 which basically doubles the efficiency (of geothermal energy projects), so maybe now we can actually produce electricity geothermally there, which was not possible before," said Saar.

Because CO2 is so much more efficient at extracting heat, the criteria for what would make a site worthwhile for extracting geothermal energy might be broader.

Shallower depths or weaker sources of heat that are insufficient for water-based projects might be good enough for CO2-based extraction, especially if sequestration was going to happen at a given site, anyway.

Others have previously made use of CO2's improved efficiency at capturing heat, but Saar and Randolph are the first to propose combining carbon-dioxide-driven geothermal energy with large-scale carbon sequestration sites.

Saar and Randolph still have many details to work out, including how deep the sites would need to be, how much subsurface heat would be needed to make it feasible, and how the CO2 would react with the minerals in the ground. (ANI)