The market for electricity

As the supply of electricity changes in response to growing numbers of wind turbines, there's more need to be able to store electricity: Wind Drives Growing Use of Batteries

"In New York and California, companies are exploring electrical storage that is big enough to allow for “arbitrage,” or buying power at a low price, such as in the middle of the night, and selling it hours later at a higher price. In the Midwest, a utility is demonstrating storage technology that can go from charge to discharge and back several times a minute, or even within a second, bracing the grid against the vicissitudes of wind and sun and transmission failure. And in Texas, companies are looking at ways of stabilizing voltage through battery storage in places served by just one transmission line."

I also recently heard of attempts to create more flexible demand by fitting households with electrical heat storage units, that heat bricks when electricity is cheap, and power the household heating system off the stored heat.