Most discussion of energy storage that I’ve seen has focused on batteries, with occasional mentions of pumped hydro. But in the last week, I’ve seen announcements of big investments in quite different technologies. Goldman Sachs just put $250 million ($US, I think) into a firm that claims to worked out the bugs that have prevented the use of compressed air storage until now
And several companies are working on gravity storage (raising and lowering massive blocks) to store and release energy
Underlying these points is a crucial fact in physics/engineering: Any reversible physical process is an energy storage technology.
That’s why concerns about the variability of wind and solar power will come to nothing in the end
Energy storage technologies differ in lots of dimensions, including efficiency (the proportion of stored energy that is released), speed of discharge, and the time for which energy can be stored without being lost. Conversely, an energy supply system has demands that vary on all the correspond dimensions. In particular, the storage time dimension can vary from milliseconds (the instant power needed to maintain system stability against shocks) to months (storage between seasons).