MINNEAPOLIS — A judge’s ruling this week means Minnesota could see a major expansion in the use of solar power over natural gas.

Administrative Law Judge Eric Lipman was reviewing whether Xcel Energy should invest in natural gas generators or solar power arrays. He concluded Tuesday that solar was the better deal for Xcel customers and the state.

If the state Public Utilities Commission upholds his finding, Edina-based Geronimo Energy plans to spend $250 million to build about 20 solar power arrays across Xcel service sites. Xcel would then likely buy the power from Geronimo under a long-term agreement.

Betsy Engelking, Geronimo’s vice president, said the ruling shows how cost-effective solar energy has become.

Xcel and three other energy companies had submitted proposals that mainly involved using natural gas to generate power. Xcel said it disagrees with some of Lipman’s findings and will file a response, which the utility commission will consider before taking a vote.

Geronimo’s solar project wouldn’t get state or utility subsidies but would qualify for a federal tax credit.

The proposed sites are in 17 counties, mostly across central, eastern and southeastern Minnesota.

Lipman said solar energy provides the greatest value to Minnesota and to Xcel customers. He noted that if solar power alone can’t supply all of the utility’s extra power needs in the next few years, Xcel could accept an offer to buy surplus energy from Great River Energy, the state’s second-largest power company.

The judge also said Xcel will have a chance to consider other generation projects if demand picks up.

The largest of the Geronimo projects would be five times the size of the state’s largest solar array in Slayton and some would cover as many as 70 acres.

This is the first time the state used a competitive bidding process on a major power-generation project. The utility commission ordered the move in an effort to force energy companies to compete on price.