McGrail and his research team stumbled on a way to boost the energy-conversion rate as the two loops pass through a heat exchanger. Initially, they had developed proprietary materials for another project to improve the capture of carbon dioxide emitted from a fossil-fuel plant. They realized that the materials had remarkable thermodynamic qualities when added to an organic fluid. The new fluid has the potential to capture up to 30 percent more heat from a closed water loop, and, because of its rapid expansion and contraction capabilities, it can achieve higher pressures for driving the turbine.
“It’s one of those moments in the lab where you look at the data and say, ‘Wow!’” says McGrail. His group has received a $1.2 million grant from the Department of Energy’s geothermal technologies program to build a benchtop prototype that shows the properties of the fluid in action.
“Hopefully we’ll get a test loop system together by the end of the year. We’ll put together a complete working unit with heat exchanger, compressor, pumps, and a turbine system so we can see the whole process working,” he says.
The lion’s share of the cost of geothermal is in drilling and preparing production wells, says Susan Petty, chief technology officer of Seattle-based AltaRock Energy, a developer of enhanced geothermal systems. “If you’re going to get a 20 percent or higher improvement in efficiency, that’s 20 percent less well,” she says. “That is really, really significant.”
There are potential showstoppers, however. Ron DiPippo, professor emeritus of mechanical engineering at the University of Massachusetts Dartmouth and a coauthor of the MIT report, warns that the vaporized fluid must pass through the turbine without affecting performance. “You have to really view these things skeptically and do a careful analysis of the properties of these fluids,” he says. “You may have a gain on one side and a sacrifice on the other end.”
Testing how the nanomaterials pass through the turbine will be a priority once the prototype is developed, says McGrail. “We don’t know if it will be an issue yet.”