California regional energy market to expand as new companies join

By Noah Baustin | 02/26/2026 06:52 AM EST

With the addition of South Dakota, the Western Energy Imbalance Market will include energy producers and grid operators in 12 states.

A newly expanded transmission system in the Midcontinent Independent System Operator's Western states is congested and threatens to significantly slow wind and solar development in the region. Power lines in South Dakota are pictured.

The expanded market will enable more electricity trading across the West. Jim Brandenburg/ Minden Pictures/Newscom

A California-run electricity market that allows utilities to make short-term energy purchases is expanding to South Dakota, its 12th state.

What happened: The California Independent System Operator announced Wednesday that two new companies will join its Western Energy Imbalance Market in May.

Black Hills Energy, based in Rapid City, South Dakota, operates natural gas and electric utilities and serves 1.35 million customers across eight states. PowerWatch in Great Falls, Montana, is an energy producer and grid operator owned by Berkshire Hathaway Energy.

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“We are honored to welcome Black Hills Energy and PowerWatch into the WEIM,” CAISO President Elliot Mainzer said in a statement. “The continued growth of our markets delivers real economic benefits to market participants and their customers and is a proven strategy for improved reliability and affordability throughout the region.”

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