Ice or Molten Salt, Not Batteries, to Store Energy


ENERGY storage is crucial to transforming the electric grid into a clean, sustainable, low-emissions system, the experts say. And it’s happening already, just not the way most consumers would expect. The simplest idea for storage — charging up batteries at night when there is a lot of wind energy and not much demand for it, or at midday when the sun is bright — is years from being feasible, according to the experts. . . .

The value of storage, according to AES, is to add flexibility to the system. But the way to store bulk amounts of energy for the grid lately is with cold or heat, as ice or molten salt. Hundreds of buildings now use their air-conditioning systems to freeze water into ice in the middle of the night,  taking advantage of low outdoor temperatures to help do the job. During the day, they melt the ice to cool the air.

In the Arizona desert, a major new solar plant uses the sun’s heat to warm sodium into a hot liquid. When the sun goes down, the sodium is piped into a steam generator, giving off its heat to boil water, which is used to spin a turbine and make electricity. The builders say using batteries would have made the costs many times higher.

A Houston company, TAS Energy, stores energy as cold. It chills water at night, and during the hot Texas summer, uses the cold water in a device like a radiator, to cool incoming air that is sent to a plant burning natural gas. When the incoming air is cooler, it is denser, so more of it fits into the combustion chamber, and power output is higher. The effect is to use nighttime energy to increase capacity in the hot afternoon. . . .