Searching for "storage" gives very few hits. This was perhaps the most pertinent hit:
"IT IS GENERALLY NOT ECONOMICALLY FEASIBLE TO store electricity in bulk. The widespread deployment of new storage technologies and/ or high penetrations of electric vehicles may someday change this, but these developments are unlikely before 2030."
along with this:
"Compressed air energy storage (CAES) is the only other storage technology [other than pumped hydro] that has achieved long-term utility-scale operation. ... Only two utility-scale CAES facilities have been constructed worldwide: a 290 MW facility with two hours of storage in Huntorf, Germany, that entered commercial operations in 1978 and a 110 MW facility with 26 hours of storage in McIntosh, Alabama, that entered commercial operations in 1991."
Not very much to go on, now is there.