May I take this opportunity to remind you of one or two other storage options Bob?
http://www.v2g.co.uk/tag/storage/
There are multiple possible storage solutions, but none are great. Yet. Pump-up is a distinct possibility and we have a lot of existing dams that could be converted for storage. There's also closed loop pump-up.
Probably the most promising is Ambri's liquid metal battery for large scale storage. If it progresses past the prototype level where is seems to be working and on to manufacturing scale then it could solve our problems. Dirt cheap and uses readily available materials.
Another interesting is CAES as being implemented by a company called Lightsail. They have figured out how to extract and store the heat created during compressing air and then using that heat to re-expand the air during generation.
V2G might be a good solution, but we're going to need better (larger capacity) batteries. If people have only 70 to 100 mile range they aren't going to be willing to 'rent out' much of their capacity. Get range up above 175 miles and V2G could be a big player.
There are also tests underway to store heat in gravel using argon gas as the transfer medium and heat pumps to store/generate the energy. This could also be a low cost solution.
Hydrogen and ammonia are other options. But probably too inefficient.
I think we'll have a much better idea of how to store in the next couple of years. There is a very large amount of research being done.