Roseville is thinking of turning City Hall into a power plant — and perhaps saving close to a million dollars in energy costs.

But the issue now is caught up in a wider set of questions involving a potential facilities overhaul that could cost anywhere from $6 million to $14.5 million, at a time when Roseville schools are promoting a major facilities referendum of their own.

The city is weighing a proposal to generate 450 kilowatts from solar arrays atop a pair of buildings on its civic campus. Staffers acknowledge that unknowns remain; savings over 25 years could range from $105,000 to $991,000, depending on lots of factors. And differences are emerging over how to assess the risks and payoffs.

For Council Member Tammy McGehee, the savings could end up being piffling given the possibilities that the whole concept goes south and the city winds up with a bunch of old junk metal to salvage.

For Mayor Dan Roe, by contrast, there’s a much wider range of factors to consider.

“Saving money goes hand in hand with supporting renewable energy, becoming more energy efficient, leading by example, and being good stewards in terms of the environment,” he said.

The main holdup in Roseville is what form the roof space will take once the City Council sorts out its facilities needs. The plan is for arrays on two rooftops, although the roof on the public works building may not exist much longer.

“We need additional storage space for public works equipment,” the mayor said, “and we also have a license center we perhaps want to bring onto the city campus. So in looking at solutions to those issues, we didn’t want to preclude ourselves from doing something with that building.”

The city wouldn’t want to lose a bundle on the deal, Roe said, but it doesn’t need to earn huge dividends in purely financial terms in order to proceed. Risks include the price of other energy sources dropping, but he said he wasn’t too concerned about that, “given the history here; it seems they do trend higher over time.”

In theory, the city could achieve maximum savings from solar by simply acquiring the equipment. But the CEO of the local firm working with the city cautions that Roseville may be reluctant to do that.

“Most cities will not ever own the arrays,” said Jon Kramer, CEO of Sundial Solar Energy. “They don’t have the money to buy it and don’t have a way to monetize the tax advantages of it; the tax credit depreciation [his firm would enjoy] is not allowed to nonprofits. Most cities’ arrays are third-party-owned, which also greatly mitigates the risk to them.”

The solar issue has been kicked around for years in Roseville, which has sought grants without success. Neighboring Falcon Heights has had them for a few years on its City Hall, generating most of that building’s energy needs. In Roseville a substantial city campus with plenty of roof space lends itself to the same purpose.

City staffers are hoping to add 6,000 square feet for city offices and 36,000 square feet on 6 acres for public works, promising much more elbow room than the 57,000 square feet the department has now on 3½ acres.

Price tags ranging as high as nearly $15 million, though, led Council Member Bob Willmus to muse that there may be “some options there that maybe we have casually dismissed ... but are worthy of discussion.”