The global energy storage market is doubling this year as households and businesses buy batteries to accommodate a surge in renewable energy, a London-based international market-analysis company says.

Consumers will add 2.9 gigawatt hours of energy-storage capacity this year, up from 1.4 gigawatt hours in 2015, IHS says.

The world will have 21 gigawatt hours of grid-connected storage capacity by 2025, the company predicts. A gigawatt hour — or a billion watt hours — can power about 725,000 homes.

Energy storage is needed because wind and solar power are intermittent, generating electricity only when the wind is blowing or the sun shining. Batteries allow wind and solar power to be stored for later use.

Eighty percent of the world’s stored energy will be on lithium ion batteries, whose technology keeps improving, IHS says. A key driver of sales will be ongoing declines in battery costs.

The United States and Japan will add the most energy-storage capacity in the next decade — a third of all storage added, worth $50 billion, IHS says.

Storage has great potential in Europe as well. Germany is generating much of its power from wind farms in the north, but grid-transmission limitations prevent it from sending a lot of that power to its industrial heartland in the south. That means it is having to give some of its wind-generated electricity to other countries in the region for free.

SOCAR USA is the U.S. representative office of SOCAR, the State Oil Company of the Azerbaijan Republic, and is headed by Director Rauf Mammadov. The office was founded in 2012 and is engaged in generating awareness of the company’s global activities in the United States and exploring U.S.-based energy-industry opportunities.