Problem: Wind and solar energy sources simply can't produce power at all times. Energy storage is needed to store energy from the sun and wind when it's produced for use later. No economical, widespread energy storage method currently exists that would allow a substantial portion of the electrical grid's electricty to be supplied by these renewable sources.

Solution: An inexpensive, compressed air energy storage system with 60-70% efficiency could be widely scaled, hopefully enabling terawatts of grid energy storage in the next two decades.

Technology that might make it possible: Water is used to cool air temperature during compression and increase temperature during expansion, making the system more efficient.

More at we.SolveforX.com