That depends on what problem you're solving and how much you're willing to spend. Some people seem to thing grid storage is a failure if it can't store power i

That depends on what problem you're solving and how much you're willing to spend. Some people seem to thing grid storage is a failure if it can't store power in the summer to use in the winter, but that's really not a realistic goal. Storing power during the daylight to use at night is far more reasonable -- expensive, but doable with current technology. Pumped hydro storage is another option. As is relying not so much on storage but rather expanding grid interconnection. Day/night solar cycles are less of a problem if you can buy and sell power across many time zones.