The Kansas Supreme Court said Friday state regulators engaged in illegal price discrimination by allowing utility companies to assess higher electric fees on residential customers who generated their own wind or solar power.

The decision means Kansas utility companies can’t charge customers producing their own energy more than the companies charge other customers based on that distinction.

The court said the Kansas Corporation Commission improperly gave Kansas Gas and Electric Co. and Westar Energy, which operate as Evergy, permission in 2018 to charge residential power producers the extra fees. The Kansas Court of Appeals had sided with the KCC and utility companies, but the Supreme Court ruled in favor of Sierra Club, Earthjustice and Vote Solar.

Zack Pistora, Kansas lobbyist at the Sierra Club, said the KCC’s treatment of residential solar and wind producers was morally and economically unfair and the Supreme Court determined it also was illegal.

"With today’s Supreme Court ruling, we make headway toward fairness and justice for solar and renewable energy users in Kansas," Pistora said.

Justice Caleb Stegall, an appointee of Republican Gov. Sam Brownback, wrote the opinion holding the residential rate structure embraced by the KCC and crafted by KGE and Westar violated state law.

The Supreme Court’s decision said the attempt to differentiate customers was "simply price discrimination." The state court said the "rate design is unlawful" and the KCC mistakenly approved special assessments against residences offsetting their utility purchases by installing their own solar and wind generation.

The justices remanded the fee case to the KCC for further action.

Gina Penzig, spokeswoman for Evergy, said the company was reviewing the Supreme Court’s decision. She said Evergy may ask the Supreme Court for rehearing of the case and will work with the KCC regarding "appropriate next steps" once the commission resumes operations.

The KCC decision in favor of utility company fees created a cost barrier to Kansans interested in installation of solar panels on their homes, said Robert Eye, a Climate and Energy Project board member and Sierra Club attorneys involved in the case.

In some instances, critics of the fee said, the extra cost was in excess of $100 a month.

"This decision strikes down needless financial penalties for rooftop solar ratepayers and moves our state toward further development of solar and wind power," Eye said.

David Bender, the Earthjustice attorney who argued the case in Kansas, said Americans had a right to "the free solar energy delivered to their roofs every day without fear of illegal utility charges that serve only to preserve the utility’s anti-competitive monopoly and prop up uneconomic fossil fuels."