Renewable geothermal energy has the potential to become a major player in the energy transition.
According to recent reports from the International Energy Agency and the Clean Air Task Force, the scale of it could increase if we can tap into superhot rock over 375oC.
Most geothermal plants today work at considerably lower temperatures, most ranging from about 100 to 250oC, so relatively little is known about designing plants for much higher temperatures.
Now, engineer Daniel Dichter of Quaise Energy has reported in journals big potential changes, if these higher temperatures can be harnessed.
He said: “We have a good understanding of how to design geothermal power plants in the conventional temperature domain, but we don’t have much experience with geothermal source temperatures any higher than that. These papers apply conventional geothermal design principles to a higher-temperature range beginning at 300oC.”
Dichter hopes the work will inform a roadmap toward a superhot future.
In geothermal plants, water exposed to hot rock picks up that heat and is then pumped to the surface where the carried energy is converted into electrical power.
Among Dichter’s conclusions: for systems tapping into superhot rock, it may not be necessary to maintain water at temperatures above 375oC all the way to the surface.
He also found that plants working with geothermal fluids at temperatures higher than 300oC at the surface can use common turbines to turn the resulting steam into electricity.
Most geothermal plants operating today at lower, conventional geothermal temperatures must employ a more expensive turbine system that is not as commercially available.
Supercritical
Water pumped into rock at temperatures above 375oC will become supercritical, this can carry some 5-10 times more energy than hot water at conventional geothermal temperatures, making it a power-dense energy source if it could be pumped above ground to turbines that could convert it into electricity.
Today, however, rock at those temperatures can only be accessed at a few locations around the globe, such as Iceland, where they are relatively close to the surface. The number one problem: we can’t drill down far enough.
The study found that if we can tap into superhot rock miles down, we don’t have to maintain the water at supercritical temperatures (above 375oC) all the way to the surface.
Dichter is excited about our geothermal future. “The applications are diverse, from power plants to regional heating to domestic ground-source heat pumps – and there are a lot of fresh new eyes on the field.
“There’s a renaissance happening in geothermal right now.”
