The smart grids of the future will need a lot of energy storage, both to get the most out of intermittent sources like wind and solar, but also to even out the demand curve so that expensive, fossil-fuel peaker plants aren't as needed. Some of that storage will be people and businesses buying battery systems, some will come from power utilities building large scale solutions like pumped hydro and liquid-metal batteries (check those out if you haven't already -- very promising technology!).

But another source of storage on the grid will be electric vehicles. With the right technology to manage it and the right incentives for EV owners, it could provide quite a big amount of storage. The idea is to charge when electricity is cheap and clean, and send some of it back to the grid when electricity is expensive and dirty. Imagine in a few years: millions of electric cars with battery packs that can, on average, store 2-3x more energy than current models. This adds up to a lot!

Nissan has started to test this kind of technology: