SALT LAKE CITY — Rooftop solar advocates, ahead of a Monday marathon hearing in which more than 150 people are expected to provide input, say a proposal by Rocky Mountain Power to cut its compensation rates will end the booming renewable energy sector in Utah.

“We need to make sure our Public Service Commission gets this right. Anything short of that will have devastating consequences and that is not good for Utah,” said Tom Mills, technical sales and policy advocate at Creative Energies Solar during a webinar.

The hearing before the Public Service Commission stems from a proposal by Rocky Mountain Power to decrease its compensation to rooftop solar customers for the excess energy they export to the grid.

Until 2017, it was a one-to-one exchange per kilowatt hour for the going residential electricity rate, but that was reduced for customers coming on in a transition period pending the results of a Rocky Mountain Power study looking at costs and benefits of rooftop solar.

With that study now ended, the utility company is proposing taking that compensation from 9.2 cents per kilowatt hour to 1.5 cents per kilowatt hour — a more than 80% decrease — to avoid having what it says are unfair costs shifted to its customers who don’t have rooftop solar and are forced to fill in the financial gaps.

But Mills says the study is flawed, akin to the fox guarding the henhouse, because a utility company should not be allowed to determine proposed compensation rates for its competitors — in this instance rooftop solar customers with their own on-site generation.

That on-site generation, too, should factor in as a benefit to Rocky Mountain Power, Mills said. Instead of Rocky Mountain Power basing rooftop solar rates off the same price as utility scale solar farms, it should be looking at the benefits of avoided costs such as transmission, energy loss on the lines and having the power produced where it is consumed.

Spencer Hall, spokesman with Rocky Mountain Power, said rooftop solar customers were initially given a bump in compensation to help the industry become established and because the cost of the technology was so prohibitive in the early stages.

Those costs have come down, and as rooftop solar has taken off, those customers are not bearing the entrenched costs of infrastructure, grid maintenance and other factors that come into play when operating a grid, he said.

Instead, customers without rooftop solar — the majority of the utility company’s Utah base — are shouldering the costs in a system that has grown inequitable, Hall said.

Glen Lamson, who spoke during the webinar, is a rooftop solar owner who made his investment in panels before the rates changed.

“Three years ago I installed solar on my roof after many years of wanting to do the right thing,” he said, adding it was the compensation rate decrease that pushed him to make the move.

“If the economics are not there ... without that I would not have signed up for solar,” he said.

Lamson fears that a further reduction in the rate will result in people doing the same household financial analysis and ultimately deciding they will take a pass on renewable energy.

Grace Olscamp, spokeswoman with HEAL Utah, said about 1,250 people have weighed in so far against the proposal to decrease rooftop solar compensation rates, with the Public Service Commission likely making a decision within the next two to three weeks.