Geothermal, and high pressure undeground storage of water are two experimental techniques being studied for short-term storage of wind and solar energy. Since both sources are intermittent, the generation capacity is often not available when needed. Batteries are not the only solution, “hot rock” and subterranean pressurized caverns present alternatives.
It remains to be seen if the dangers of fracking can be avoided with these wells.
How a Technology Similar to Fracking Can Store Renewable Energy Underground Without Lithium Batteries – Inside Climate News
Three Houston startups are using fracking-like techniques to create underground storage caverns for pressurized water, which when released drives a turbine to send power to the grid.