Minnesota has an ambitious goal to get all of its electricity from carbon-free sources by 2040. Utilities are retiring power plants that burn coal and are adding new wind and solar energy.

But without batteries, the electricity generated by wind and solar farms must be used as soon as it's produced. That’s not always when it’s most needed.

"Think of the battery as like a stockbroker who can absorb excess energy, or buy that electricity when it's really cheap, and then discharge that energy when the demand is high, when electricity might be more expensive,” said Aaron Hanson, energy program specialist with the University of Minnesota's Institute on the Environment.

Batteries that store electricity and release it on demand are becoming an increasingly important part of the transition to c

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