As prices for wind and solar power drop, some experts say that the biggest barrier to making renewable energy dominant is the need for cheap and reliable storage.

A new Department of Energy agency, the Advanced Research Projects Agency for Energy (ARPA-E), seems to be listening. It could soon start a new funding round devoted exclusively to energy storage technologies, according to Imre Gyuk, a program manager for energy storage research at the Department of Energy. As a first step, it has also announced a workshop on grid scale energy storage to be held in Seattle on October 4.

Solar and wind technologies seem headed to the point where, in the next several years, they will be able to generate electricity at costs comparable to those of conventional sources.

But there’s a catch. Electricity from wind turbines and solar panels isn’t worth as much as electricity from coal or natural-gas-fired power plants or from nuclear reactors because it’s not always available. When clouds cover the sun, or the wind stops blowing, utilities have to turn to conventional power plants to make up the difference. And, of course, solar doesn’t work at all at night.

As the cost of solar comes down–and if researchers can develop cheaper storage–one day it might be practical to build extra solar panels and store the electricity they produce for use on cloudy days and at night. Then, because there’s more than enough sunlight for all our energy needs, solar could become a primary source of electricity.