Thousands of panels making up the biggest solar energy site in Minnesota may spring up alongside a highway in Shakopee.

The Metropolitan Council hopes to find the money to plant the 15-acre project down the road from Valleyfair amid skeptical questions from its citizen board. "I have a hard time understanding this," Council Member John Doan of Blaine remarked as the idea was being explained in committee late last year.

The main reason: On paper, it looks as though the project falls far short of recouping its nearly $7 million cost.

But an expert in the field said late last week that the arithmetic feels off-base to her. "The [cost seems] high, the payback seems low," said Laura Cina, managing director of the Minnesota Renewable Energy Society, after reviewing the council's paperwork at the Star Tribune's request.

"They are salvaging the panels at 25 years," she added, "which is strange because they will keep producing well past that ... . I think there may be some mistakes here."

The solar array is being planned for an empty piece of ground alongside the council's Blue Lake sewage treatment plant, one of the last things a visitor to Shakopee sees before arriving at Valleyfair or Canterbury Park on Hwy. 101.

It would be a 1.25-megawatt facility, with nearly 5,400 panels, furnishing as much as 13 percent of the plant's need for power, council officials say.

As such, Cina said, it would be the state's largest, exceeding the size of the array that the Ikea store near the Mall of America plans to put on its roof. Ikea said last month it plans to install a 1.1-megawatt array, and expects a slow payback given Minnesota's relatively modest electric rates.

Given the cost, council documents show, it "requires a grant amount of $4,400,000 to make the option an economic break-even consideration" -- at least for sewer ratepayers.

Cina said she doubts the cost needs to be so high: "Installers tell me that if they go out for bids it would be way lower."

The size of the break-even gap puzzled some on the council, who were led to ask who would supply the money and why the council should do it in the first place.

William Cook, the staff member on the hot seat when the plan was discussed in committee last November, admitted he couldn't fully deal with the question.

"We have a number of goals," he said, "some energy-savings goals, to reduce reliance on fossil fuels; we have an energy-reduction program and this is an element of that, [and] a number of other reasons I'm not particularly well versed on with regard to some of the environmental issues."

Council Member Sandy Rummel of White Bear Lake, a former state senator appointed to the council by DFL Gov. Mark Dayton and now chairing the council's environment committee, offered a more robust defense. She mentioned a New York Times column by economist Paul Krugman arguing that "we're just a few years from the point at which electricity from solar panels becomes cheaper than electricity generated by burning coal. And if we priced coal-fired power right, taking into account the huge health and other costs it imposes, it's likely that we would already have passed that tipping point."

She added: "This is a tremendous opportunity, and I support anything we can do to move in that direction. ... The harmful things that happen using other forms of energy are removed, and it's hard to put a price tag on that."

David Peterson • 952-746-3285