Similar to traditional pumped hydro storage systems, where water is moved between two reservoirs (one higher and one lower) to either store or generate electricity.
Humans have, over the last 100 years (and many billions of dollars), perfected robust equipment and methods of moving water (and oil and gas) underground, through rocks. Now we can use the same proven equipment and methods to move the water underground, but this time for energy storage.
The water underground is stored in micro-pores in rock under intense pressure. An above-ground system relies on gravity. Underground, we also have the benefit of a much more powerful force – geo pressure.
Large pressure differences exist between isolated rock layers or zones that are saturated with water, e.g. 400 atmospheres vs. 200 atmospheres. When we connect those two isolated zones, water flows extremely quickly from the higher pressured zone to the lower pressured zone. This high speed powers our turbines very efficiently and we send the electricity generated to surface by cable. Then, when there’s a surplus of electricity at surface, for example from wind or solar, we send it down hole by electric cable again. That electricity powers a pump that re-establishes the pressure difference between the two zones, recharging the system for future electricity generation.
