Arizona has become the first US state to introduce a charge on rooftop PV users in what America’s solar industry has described as a “precedent-setting” action.

At the end of a two-day hearing over an increasingly contentious issue, the Arizona Corporation Commission voted 3-2 in favour of allowing state utility Arizona Public Service to impose a US$0.70 per kilowatt charge on solar net metering customers.

APS had argued that the charge was necessary to offset the cost the growing number of solar systems passed on to non-solar ratepayers. The utility said that net metering customers, which are able to claim credit on excess power fed back into the grid, effectively shift the cost of maintaining the grid on to ratepayers that do not use solar.

The ACC commissioners narrowly upheld this claim, voting for a charge that will be imposed on all new systems built after 31 December this year. The fee is expected to hit solar users to the tune of around US$5 per month.

But APS’s immediate response to the commission’s decision was to claim that it did not go far enough.

“Having determined that a problem exists, we would have preferred for the ACC to fix it,” said Don Brandt, chairman and chief executive of APS. “The proposal adopted by the ACC…falls well short of protecting the interests of the one million residential customers who do not have solar panels. We will continue to advocate forcefully for the best interests of our customers and for a sustainable solar policy for Arizona.”

Nevertheless, the commission’s decision ACC has been roundly criticised by industry and environmental bodies alike.

Rhone Resch, chief executive of the Solar Energy Industries Association, said he was “deeply troubled” by the “precedent-setting action”, implying that the decision will have attracted the interest of utilities and ratepayers beyond Arizona.

“Imposing punitive fees on Arizona consumers – without first proving the need and demonstrating the fairness of these charges through a comprehensive, transparent rate case where due process is afforded – is patently unfair, jeopardising future solar growth and job creation statewide,” Resch said.

Will Greene, the Arizona representative of environmental body the Sierra Club, said the move would “stifle” the growth of solar in the state.

“We acknowledge APS originally proposed a much-larger charge, but our state’s burgeoning private solar industry will still need to overcome this new challenge. Rooftop solar brings important energy savings to working families and it gives us the freedom to be more energy independent.”

Arizona has become the biggest battleground over the solar net metering issue in the US, with APS revealed to have been secretively funding an anti-solar lobbying campaign.

The issue has also polarised public opinion. At the start of the ACC hearing on Wednesday, an estimated 1,000 pro-solar campaigners turned out to protest against the charges proposed by APS.