Great River Energy's member cooperatives have approved the sale of the company's giant North Dakota coal power plant, but its largest member — Connexus Energy — voted against the deal.

Maple Grove-based wholesale electricity provider Great River announced Friday that its members, which are retail power co-ops serving several parts of the state, approved the sale of Coal Creek station and an accompanying high-voltage power line to Bismarck, N.D.-based Rainbow Energy Marketing.

Great River had planned to close Coal Creek in a big strategic pivot last year, saying it couldn't sell the unprofitable power plant for even $1. But North Dakota government officials rallied to save it, and a deal with Rainbow was forged in June. It's price wasn't disclosed.

However, Michael Noble, head of St. Paul-based renewable-power group Fresh Energy, said Great River management told him the sale price was around $225 million — the book value of the power line. Another source who has seen sale documents confirmed that number.

Great River's 28 member co-ops provide electricity to about 700,000 Minnesotans.

Connexus — which serves parts of Anoka, Chisago, Hennepin, Isanti, Ramsey, Sherburne and Washington counties — was the only member co-op to vote against the Coal Creek sale. Another member abstained.

Ramsey-based Connexus Energy, which has 138,000 customer-members, posted on its website Friday that its board voted unanimously to oppose the sale.

"The Connexus Board of Directors finds the decision and approach to sell Coal Creek Station and related transactions have neither fulfilled the savings Connexus expected for its members nor reduced greenhouse gases by enabling the continued operations of that plant."

Great River announced in May 2020 that it would close Coal Creek in 2022, part of a plan to significantly increase its wind power operations (which have not changed) and boost its natural-gas generation. Gas emits about half the carbon dioxide as coal and is cheaper.

The company's plan was hailed by clean-energy groups as Great River would have been the first Upper Midwest utility to close a major coal-fired plant.

Great River also announced in May 2020 that by unloading Coal Creek, its 28 members would yield substantial benefits: Wholesale rates they pay would be flat until 2023, but then fall by 13%.

But Connexus said the current deal, which must gain regulatory approval, is not as good for the co-op.

Great River's proposal to close Coal Creek would have reduced delivered power costs to Connexus by an expected $28 million in 2023, the co-op said. That number is now expected to be $20 million in 2023.

Great River said Friday that "the price of energy in the market and other conditions have changed" since the announcement to close Coal Creek, so member cooperatives would see a lower benefit.

For North Dakota, Coal Creek's closure would have been a significant blow. The plant employs 240 people, and an adjacent coal mine — which would have also closed — has over 400 more workers.

Rainbow will operate Coal Creek, which is near Underwood, N.D., as a merchant power plant, selling electricity into wholesale markets. Through a power-purchase contract, Great River will be a customer for 10 years.

Under a 10-year contract, Great River will also also continue to maintain and operate the 436-mile power line from Coal Creek to the Twin Cities.

Rainbow has said it will be operating Coal Creek under a different business model, without the overhead costs that Great River has in serving a network of retail co-ops. Great River had been losing money for several years at Coal Creek — $170 million in 2019 alone.

The crucial piece for Coal Creek's future is the installation of carbon-capture equipment and technology. Rainbow expects that equipping Coal Creek for carbon capture would cost $1.5 billion, and ample federal "45-Q" tax credits will be critical for funding.

Carbon dioxide can be captured through an industrial process and stored in underground rock formations. Still, carbon capture is a relatively nascent technology that's economically challenging; it's seen its share of failures.

Connexus said the Coal Creek carbon capture project is "commendable."

However, it is "an extremely speculative project, whose financial success depends on federal 45-Q tax credits, while parasitically consuming about 30% of the electricity generated for the process and storage," Connexus told its members.

Great River declined to provide details of the co-op vote. But there was opposition to the sale at Dakota Electric, Great River's second-largest member co-op with 108,000 customers in Dakota County and parts of three other counties.

"The plan to retire Coal Creek and invest in clean sources of energy helped move us forward — this is a grave step backward," said a letter to the Dakota Electric board from six DFL legislators who are Dakota members.

Five Republican legislators wrote Dakota's board to approve the deal, saying it saves jobs. "The all-weather resiliency of Coal Creek Station also ensures Minnesotans have access to electricity in blistering cold like the recent polar vortex," they wrote.

Dakota's board voted 8-3 in favor of the Coal Creek sale.