Oh thanks for the link! This is a good one. According to the article we’re already using:
Pumped hydroelectric
Compressed Air Energy Storage (CAES)
Flywheels
Supercapacitors
And just plain batteries
And the article ends with,
“The price of storage is coming down. The price of solving the problems in other ways is going up. Pretty soon, these prices are going to cross,” notes Boyes, suggesting cost could spur the addition of storage to the grid.