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Missoula’s energy-hungry treatment plant set for 1,200 panel solar array

Gene Connell, manager of the city’s wastewater treatment facility and Missoula City Council member Jordan Hess, discuss the bacterial process used to treat wastewater in this file photo. (Martin Kidston/Missoula Current file)

Missoula officials are planning to install 1,200 solar panels this summer on the wastewater treatment plant, which is the city’s single largest carbon emitter and energy user. The city will choose an installation company and third-party financer for the project next week.

The wastewater treatment plant accounts for about 20% of the municipal city government’s emissions. The combination rooftop and on-the-ground solar system is expected to produce 20% of the energy needed for the plant’s operation and save the city between $25,000 and $150,000 over 25 years.

The project will use a third-party financing system, which means the city will not pay for the installation.

According to the city, the third-party financer will qualify for an investment tax credit that takes 26% off the installation price—an estimated $950,000—from federal taxes. For the first five years, the city will pay the third-party for power and later buy back the system at a lower cost.

The project has been in planning for nearly a year. Construction is anticipated this summer, said Gene Connell, the plant superintendent.

“The City Council has adopted these goals around clean energy and as the Department of Public Works and Mobility, we consume more energy of the city offices and city departments than any other because of the energy involved in pumping water,” said Ross Mollenhauer, engineer with the Public Works and Mobility department who is leading the project.

The rooftop array will go on the truck barn, in the top left corner, and the ground mounted system will stand in the grass to the right of the truck barn. (Google Maps)

OnSite Energy, a Bozeman-based company that performed a feasibility study for the plant’s solar potential, expects the panels will provide 650 megawatt-hours of power during the first year. Due to the size and capacity, the system will be non-export, meaning energy produced will be used exclusively at the plant.

According to OnSite’s projections, the city can expect to save $1.6 million in energy expenses over the 25-year lifespan of the panels.

The remaining 80% of power necessary for plant operations, and the cushion in the winter months when solar production takes a dip, will continue to come from NorthWestern Energy.

The plant’s solar installation will offset about 700 metric tons of carbon dioxide, or 3% of the municipality’s overall emissions, according to Leigh Ratterman, a city climate action specialist. The drop is expected to help the city make progress on its clean energy goals.

In November, the county also installed the largest solar rooftop array in the state on the Missoula jail. The jail array shares the non-exported and third-party financing components with the upcoming treatment plant installation.