By David Shaffer  for Star Tribune:  The least-expensive battery to store energy from the electric power grid may be sitting in homeowners’ basements — the electric water heater.

That is the surprising finding of research released Wednesday by the cooperative power industry, including Maple Grove-based Great River Energy, and an environmental group.

Customers at many utilities already save money by heating water at night, taking advantage of low, off-peak electric rates. It requires a special electric water heater that holds a day’s worth of household water, but offers long-term savings.

Now, a study by the Brattle Group, an economic consulting firm, says that the nation’s 50 million residential electric water heaters can address bigger challenges on the power grid, such as storing intermittent renewable energy from wind farms and solar arrays.  Cont'd...