For years, renewable-energy advocates and Utah’s largest utility have argued about the value of electricity generated on customers’ roofs, staking out positions that could have a huge impact on the future of solar power as more residents consider investing in photovoltaic panels.

The stakes for the solar industry are huge, yet no one has initiated the analysis that could settle the debate — until now, under a survey of Rocky Mountain Power customers proposed by the advocacy group Vote Solar.

“It’s really important to have the best available understanding of how and when rooftop solar is interacting with the grid,” said Briana Kobor, a regulatory director with Vote Solar, a nonprofit dedicated to making solar more accessible and affordable.

Rocky Mountain Power contends that rooftop-generated power is not worth much, while clean-power advocates and the solar industry counter that rooftop systems provide broad benefits to the public at large and to the utility in the form of reduced stress on the electrical grid and power-generation needs.

The critical issue: How much should the utility compensate its solar customers for the emission-free electricity they don’t use and RMP sells to neighbors? That rate would have a major bearing on whether other homeowners decide to spend thousands of dollars rigging their roofs with panels.

Over RMP’s objections, Vote Solar now is seeking to gather electrical generation and export data from thousands of Utah’s solar-equipped homes in an effort to demonstrate how it believes this electricity is not just good for the planet but also for all of RMP’s customers — whether or not they made the investment in solar panels.

The utility balked at releasing customer information it considers private and proprietary, but it did agree to send a letter earlier this month to its 37,000 solar customers, informing them about the study Vote Solar is undertaking as part of the group’s intervention in a rate case pending before the Utah Public Service Commission.

Rocky Mountain Power protects its customers’ identity, location, and usage data and will only provide identifying information to Vote Solar with the property owner’s advance knowledge and express consent,” reads the letter. It goes on to invite those customers to opt in if they are comfortable with a third party accessing the data about their 2019 use and generation of electricity.

“We’ve had an overwhelming response. My phone’s been ringing off the hook from people that are interested in helping but [are] a little bit confused about the language in the letter that they received,” Kobor said. “By opting into the study, they can help us to make it more beneficial for their friends and neighbors who have not yet gone solar and then protect their own rates going out some number of years.”

Currently, solar-equipped customers whose systems predate Nov. 15, 2017, earn a one-for-one credit for each kilowatt hour they export to the grid. Those who signed on later are awarded 9.2 cents for each kilowatt hour they generate but can’t use.

The contentious rate case will determine the price per kilowatt hour RMP must pay for rooftop-generated power starting 2032 for customers who signed on to solar before the 2017 cutoff. For those who came aboard after that cutoff date, the new — and possibly reduced rates — take effect in 2021.

“They’re going to be deciding what the fair price is to pay customers for their exported energy,” Kobor said. “Electricity has very different prices, depending on the time of day, the time of year and the location on the grid. You have some areas of the grid that are more congested than others.”

The utility is expected to ask the PSC to reduce that rate for Utah customers when it files its proposal in February. In a case pending in Idaho, it is asking that state’s regulators to set the price at 2.5 cents per kilowatt hour.

“They’re trying to lowball the value of solar moving forward, and it’s going to have consequences ... for all solar customers,” said Salt Lake City resident Stan Holmes of the group Utah Citizens Advocating Renewable Energy, or UCARE.

(Rick Egan | Tribune file photo) Stan Holmes' home in Salt Lake City is among 36,000 served by Rocky Mountain Power that is equipped with rooftop solar panels. Electricity generated by such panels but not used by the resident is exported onto the electrical grid and the utility customers are compensated for each excess kilowatt-hour they produce. The advocacy group Vote Solar is seeking generation and export data on all of the utility's solar customers to build a case for keeping compensation rates high.

RMP has its own study underway analyzing the electricity solar-equipped customers produce and export. But with only 110 homes involved, this study’s sample size is too small, critics say, and not representative to produce reliable results.

The company emphasizes that power generated on Utah roofs covers just a small fraction of the power consumed by RMP’s customers.

"Some [invest in rooftop solar] for environmental reasons and others for cost savings," said utility spokesman Spencer Hall. "Those are all fine, but it's important that you put it in context of total generation."

The real expansion of renewable power is occurring at the “utility scale,” he added, not so much by the customers themselves with tiny rooftop systems.

"It is a drop in the bucket," Hall said. "The utility-scale generation we buy is already 10 times what is done on rooftops."

The utility plans to add 3,000 megawatts of solar capacity by 2037. That’s 10 times the capacity of all the rooftop systems, including more than 1,000 on commercial structures, currently installed in RMP’s Utah service area, according to Hall.

Solar advocates say widespread adoption of rooftop solar would generate enough power to substantially lessen RMP’s reliance on coal, while imposing a minimal footprint compared with sprawling photovoltaic arrays covering hundreds of acres.

“It’s in the long-term interests of all ratepayers to have more solar and to have it incentivized rather than disincentivized, which is what we’re afraid Rocky Mountain Power is going to try to do,” Holmes said. “They’re just heavily invested in coal and also natural gas. These things are not only degrading our broader environment through climate change, but also we’re basically propping up a system that’s going to cost us dearly at the local level.”