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A proposal to convert a natural gas plant in central Minnesota to burn diesel fuel oil is sparking some opposition from environmental groups, who say it will increase air pollution.

Great River Energy operates the 170-megawatt natural gas peaking plant in Cambridge, about 45 miles north of the Twin Cities. It acts as a backup supply of electricity during times of peak demand.

Great River applied to the state Public Utilities Commission for a minor permit alteration to convert the plant to also burn diesel fuel oil. The cooperative said the change would provide flexibility during times when natural gas isn't available or its price spikes. 

Great River Energy supplies power to 28 member cooperatives in the Upper Midwest. It has reduced its use of coal and increased its wind and solar energy over the past several years, but needs peaking plants to maintain reliability during times when those resources aren’t available, said Zac Ruzycki, director of resource planning.

“We need fuels of last resort on the system when the power needs to continue to be produced if natural gas is unavailable or prohibitively expensive,” he said.

All of Great River’s other peaking plants are capable of burning dual fuels. Ruzycki said the others burn fuel oil roughly 24 to 48 hours per year. 

But some environmental groups have objected to the proposal, saying the change isn't minor and should undergo a more extensive environmental review.

“Burning diesel is a lot dirtier than the existing plant, so it could increase both local air pollution that hurts people and also will increase the amount of carbon that's burned at the facility,” said Hudson Kingston, an attorney for the nonprofit Public Employees for Environmental Responsibility.

Sarah Mooradian, government relations and policy director for the environmental group Clean Up the River Environment, or CURE, called the proposal a step backward from the state’s energy goals.

“This is not a future of clean energy that we need, and that the Legislature this year confirmed we need and wants to push us towards,” she said.

A new Minnesota law requires utilities to generate 100 percent of their electricity from carbon-free sources by 2040. However, some utilities expect to use renewable energy credits to offset their use of gas or oil-peaking plants beyond the deadline.

Environmental groups also worry that the amended permit would allow the Cambridge plant to burn oil longer than the 24 hours a year Great River Energy says it anticipates.

Great River Energy completed an environmental assessment worksheet on the project after citizens requested one. Ruzycki said the EAW showed it would not have significant impacts on air quality.

Environmental groups say batteries would be a better way to store electricity for times when the sun isn’t shining, or the wind isn’t blowing.

Ruzycki said lithium-ion batteries are cost prohibitive, and the four hours of storage they provide isn’t long enough to endure Minnesota’s cold snaps.

 as a lower–cost, longer-duration alternative that can store electricity for four days. Great River Energy plans to install 1.5-megawatt iron-air battery system next to its Cambridge plant as a pilot project sometime next year.

The Public Utilities Commission will decide whether to approve the amended site permit. The project also needs air and water permits from the Minnesota Pollution Control Agency. If those are approved, Great River Energy anticipates the project will be completed by 2025.

The commission is accepting initial public comments on the environmental assessment worksheet through June 20. Reply comments are due by June 30.

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Kirsti Marohn

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Great River Energy says the change would provide flexibility during times when natural gas isn't available or its price spikes. But environmental groups say it would increase air pollution.

Plan to convert Cambridge natural gas plant to burn diesel gets pushback

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