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:
“Vehicle-to-Building” has been in use at the Nissan Advanced Technology Center in Atsugi City, Japan, since July. The facility benefited from a reduction of 25.6KW during peak summer periods by controlling the charging time of the EVs, with no impact on the workers’ daily commute, or their vehicles. The results have led to approximately a 2.5-percent reduction of electrical power use during peak hours, a saving of nearly 500,000 Yen per year in electrical power cost (based on current Tokyo Electric Power Company’s rates). (source)
The system is smart enough to make sure that the EVs are charged when their owners need them. Ideally the software of these systems will give as much control to EV owners as possible, allowing some to be very conservative with the vehicle-to-grid (V2G) features, while others might want to squeeze the most out of it to reduce their electricity bills (ie. time-shift power usage from low time-of-use rates to high time-of-use rates).
This technology can also be useful during emergencies and power outages.
Above are two different photos of the battery pack that powers the Nissan LEAF EV. It can store 24 kWh of energy, and each battery pack consists of 48 modules, with each module containing four cells, for a total of 192 cells.