Net-metered residential solar customers of Rocky Mountain Power in Utah would see a new $4.65 monthly “facilities charge” on their bills under a plan now before state utility regulators.

Like other electric utilities around the country, Rocky Mountain Power argues that it faces fixed costs for maintaining the grid regardless of how much electricity it sells. Customers who have photovoltaic (PV) arrays on their roofs, it says, avoid paying their full share.

According to an article in The Salt Lake Tribune, there are about 2,700 residential customers in the state with net-metering contracts, or about 0.5% of the total.

Rocky Mountain Power calculated the proposed fee by comparing the average monthly amount of electricity used by residential customers (698 kilowatt hours) against the average used by net-metered customers (518 kWh). The difference in the portion of their bills to cover fixed costs became the basis for the proposed fee.

Salt Lake City Mayor Ralph Becker and others said the utility was ignoring the benefits solar power provides society and the environment by reducing the state’s reliance on coal, the newspaper said. But Rocky Mountain Power said it was a matter of “social justice,” and that customers who couldn’t afford PV installations shouldn’t have to subsidize those who can.

Last year, owners of PV arrays in Utah put almost 1 million kWh into the grid, about the amount of electricity that 100 Utah homes use in a year, according to the utility.

Rocky Mountain Power credits net-metered customers for excess generation by subtracting the number of surplus kWh from the following month’s bill. But it zeroes out the accounts at the end of each March, so customers who have banked energy surpluses throughout the year lose whatever credits they have and start the next billing year with a clean slate.

Rocky Mountain Power says only about 1 in 6 net-metered customers lost credits last year.

The Utah Public Service Commission is expected to rule on the fee by early next month.