Our lord and saviour Mr. Musk has the right idea with his domestic power developments. Big, household batteries. By the thousand/million, they could serve the same purpose as the cars. Bearing in mind currently EC batteries need replacing after a certain amount of use, at HUGE cost to the owners. I'm not sure people would want their battery lives being ruined by grid usage. However, Powerwall seems like the way forward as they're designed for interface with the power grid. Tesla could do some good over here in the UK.