Storing Solar and Windmill Energy

Both solar and windmill energy generating systems suffer from one drawback – they’re inconsistent. The biggest problem isn’t how to produce electricity from them for the power grid; it’s how to store energy from these two sources until it is needed.

The energy storage problems (and solutions) are different for solar and wind energy. Typically, solar energy systems generate heat, which powers steam turbines to produce electricity. For solar energy systems, the problem becomes how to store heat until it is needed. The current technology stores heat in tanks of molten salt heated to about 700 degrees Fahrenheit, or in solid blocks of concrete.

Windmills generate electricity directly without heat, but of course they only work when the wind is blowing. A variety of battery technologies are currently available to store excess electricity generated by windmills during peak generation periods. But so far, batteries can’t store enough energy to power a major power grid for any significant length of time. For long-term energy storage, excess electricity from windmills is used to pump water uphill to storage reservoirs. When power is needed, the water can power turbines to produce electricity. One innovative alternative is storage of compressed air in huge underground caves!

Renewable energy production and storage – no doubt we’ll hear a lot about it in the years to come. For more on this subject, see the articles on storing solar and windmill energy in the Nov. 18 issue of Science.