What's believed to be the largest rooftop solar array in Montana will soon sit atop the Missoula County jail, where it will generate nearly 21% of all electricity consumed by the facility.

Missoula County approved the contract with Serock Energy last week, calling it a novel financial arrangement and a big step forward in achieving 100% clean electricity by 2030.

“This has never been done before. This is breaking new ground,” said Commissioner Josh Slotnick. “This type of third-party financing has never been done before. We did it while creating the largest rooftop solar array in the state.”

Under the agreement, Serock Energy will install and own the array, and the county will pay 8.5 cents per kilowatt hour for the first five years. In the sixth year, the county will have the option of purchasing the array.

The array, estimated at around $450,000, will include 1,152 solar modules that produce a total of 432 kilowatt hours of electricity. That accounts for around 20% of the jails total electrical consumption. The jail is the county's single largest consumer of electricity.

“Based on current interest rates and rates we expect to see in the next five years, we're projected to save around $391,000 over 25 years going with this model,” said Jason Emery, the county's chief information officer. “Serock is able to take advantage of some tax benefits and other savings we cannot. We're able to factor that into the over all cost of the system.”

With its goals on carbon neutrality in government operations and a community goal of achieving 100% clean electricity by 2030, the county began looking at a solar array on the jail early last year. It contracted On Site Energy to complete an assessment and design.

The financing model with Serock is unique in Montana, though it has been practiced in other states. The arrangement enables the county to get into a sizable system without investing much capital up front.

“It will be a non-export system, meaning if we do generate any extra power, which I don't believe we will, it won't be exported to NorthWestern Energy. That's something that's not possible,” Emery said.