Researchers from the Lawrence Livermore National Laboratory (LLNL), Ohio State University, the University of Minnesota and TerraCOH Inc. have designed a system that they say can store renewable energy and sequester carbon. The system, described in Mechanical Engineering, could tap geothermal energy, store energy from above-ground sources and dispatch it to the grid throughout the year like an underground battery, while at the same time storing CO₂ from fossil-fuel power plants.

“If you want to store the large quantities of renewable energy necessary to balance seasonal supply-demand mismatches—and store [them] efficiently—we believe the best way to do that is underground,” says the paper’s author, Thomas Buscheck, leader of LLNL’s Geochemical, Hydrological and Environmental Sciences Group.

The team’s approach involves injecting liquid-like CO₂ into underground reservoirs located in sedimentary rock. This creates a pressurized plume that pushes brine upwards in production wells to the surface. The brine could be heated and reinjected into the reservoir to store thermal energy, and the pressurized CO₂ would act as a shock absorber, enabling the system to be charged or discharged depending on supply and demand. When there is insufficient renewable energy, the pressurized CO₂ and brine could be released and converted to power.

“Storing such vast quantities of CO₂ creates so much pressure. This is the biggest challenge for keeping it permanently underground, but it is manageable,” Buscheck says. “To make sure we don’t have too much pressure, we can divert some of the produced brine to generate water through desalination. Then, if we tap into the remaining pressure, we can recharge the system selectively and put energy into our storage system when there’s excess and deliver it when it’s needed.”