But todays batteries are typically quite small and store enough energy for only a few hours of electricity.
Its calledpumped hydro energy storage.
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There are several techniquesthat grid managers can use to keep that balance with variable sources like wind and solar.
These include sharing power across large regions via interstate high-voltage transmission lines, managing demand and using energy storage.
It is also cheaper for overnight and longer-term storage.
They make up 93% of utility-scale storage in the country.
Globally,pumped hydros shareof energy storageis even higher about99% of energy storage volume.
A project planned in Bell County, Kentucky, for example, uses anold coal strip mine.
Little additional landis needed except for transmission lines.
The reservoirs can be new or useold mining sitesorexisting lakes or reservoirs.
On sunny or windy days, water is pumped to the upper reservoir.
At night, the water flows back down through the turbines to recover the stored energy.
This isone-tenthof the water evaporated per person per day in the cooling systems of U.S. fossil fuel power stations.
In 2020, aboutthree-quartersof all new power capacity built was either solar photovoltaics or wind power.
Their costs have been falling, making themcheaper to build in many areasthan fossil fuels.
None involve new dams on rivers.
The annual operating cost is low, and the working fluid is water rather than battery chemicals.
Shifting electricity to renewable energy and then electrifying vehicles and heating can eliminate most human-caused greenhouse gas emissions.
