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Michelle Tessier, Deseret News
People listen to speeches during a rally for solar energy at the Utah Public Service Commission office, Tuesday, July 29, 2014.

SALT LAKE CITY — Critics of a so-called "sun tax" railed against Rocky Mountain Power on Tuesday and later packed a Public Service Commission hearing to protest what they say is a punitive, unfair proposal.

As more and more households choose to plug into the sun to meet a portion of their energy needs, Rocky Mountain Power says it still needs to cover its fixed costs of delivering power, even if the usage among those customers is going down.

The proposal is front and center before the Utah Public Service Commission and calls for a monthly fee of $4.65 to be added to the bills of residential solar customers who are on Rocky Mountain Power grid.

Monumental, voluminous filings comprise the case — to be decided in September — from a stable of seven groups at the table, including the utility company, the state Division of Public Utilities, the Utah Office of Consumer Affairs and Utah Clean Energy.

The irony in it all is that for polarized sides, the addition of a monthly fee is branded as a matter of fairness: It either allows the utility company to avoid passing on more of those fixed costs to non-solar customers or enables them to unfairly punish solar users who are doing more to reduce their carbon footprint.

It is a fight pitting solar advocates and the growing solar industry against traditional utility companies in multiple states across the country, finding a voice with Republican Party faithful Barry Goldwater Jr., a former congressman who leads Tell Utilities Solar Won't Be Killed.

At Tuesday's rally in front of the Heber M. Wells building — where an hourslong hearing of public testimony was to later unfold — Goldwater stoked the crowd.

"You can't tax the sun," he said, his voice rising. "No one owns the sun, and to put a tax on it is wrong. … The last thing we need is the government taxing us out of existence."

While Rocky Mountain Power was praised in one sense for its embrace of programs that encourage energy efficiency practices and alternative energy, Goldwater said the "monopoly" utility is committing a gaffe of epic proportions by penalizing solar customers instead of cutting them a break.

"These big utilities, if they don't get on board, they will be left behind," Goldwater said.

While residential solar customers only comprise a small share of Rocky Mountain Power's customer base in Utah — about 2,200 households — the utility company expects a signficant expansion of residential solar in the years to come, especially as prices continue to drop and the technology gets better.

An analysis coincidentally released Tuesday by the Worldwatch Institute said that 2013 witnessed record-breaking growth for solar electricity generation, with the photovoltaic market representing one-third of all newly added renewable energy capacity — or 39 gigawatts.

Rocky Mountain Power spokesman Paul Murphy said as that market continues to take hold in Utah, it is unfair to expect that non-solar customers be expected to pay a disproportionate share of the fixed costs to deliver electricity.

"This would ultimately lower the costs for people who can't afford solar or who chose not to have solar," he said.

Advocates — and solar customers who testified at Tuesday's hearing — want the Public Service Commission to reject the proposal by Rocky Mountain Power to add the net-metering fee to monthly bills and instead engage in a full cost-benefits analysis that examines the "externalized" costs of carbon-based fuels, such as pollution and attendant health impacts.

"When you look at the enormity of what is at stake, future generations will look back and ask, 'What did we do?'" said David Bennett, a Park City resident with a rooftop solar array, testifying before the Public Service Commission. "You need to send a statement to the people of Utah that we encourage renewable energy, we encourage solar power."

Email: amyjoi@deseretnews.com, Twitter: amyjoi16