Last month marked the first anniversary of Woodbury's new Public Safety Building -- and the arrival of a new source of electricity that enables police, fire and emergency workers there to do their jobs.

Workers spent the weekend before Halloween hoisting 185 solar panels, each about 3-by-4-feet in size, atop the building on the roof over the parking garage. Then they worked several days to get the system wired and operating.

The solar array will generate about 40 kilowatts of power under ideal, sunny conditions, "so it's a pretty good size," said Rick Moats, project engineer with Adolfson & Peterson Construction, who led the installation crew.

The solar panels will not only generate power for the new building, but the city's bottom line cost of about $40,000 will bring a return in energy savings estimated at more than $100,000 over 20 years, said Bob Klatt, the city's director of parks and recreation.

Similar solar panel systems have been installed in Oakdale, Maplewood and Little Canada.

"It actually puts out cleaner energy than what you get from a power plant," Moats said. Adolfson & Peterson, with an office in St. Louis Park, has completed hundreds of successful solar projects across the country.

The panels are laid out in about a dozen rows, tilted at a 10-degree angle to catch the maximum amount of the sun's rays at the building's location near the corner of Radio Drive and Valley Creek Road.

They produce direct current, which must be converted into alternating current used in buildings and residences. To do that, Moats said, an inverter is installed that can handle about every three dozen panels.

On really sunny days, Moats said, the panels -- manufactured by tenKsolar in Bloomington -- will generate more power than the building can use. That excess will be sold back to Xcel Energy and used elsewhere on its power grid.

Not only are the panels warranted for 25 years, they drew financial incentives from Xcel and the federal government and a guarantee from Adolfson & Peterson that Woodbury will save energy and costs.

The solar panel installation won unanimous approval from the City Council in September.

Under the deal, the project's cost is $290,466. Two Xcel Energy rebates and federal tax credits will go to Adolfson & Peterson, which will initially own the system, Klatt said. That allowed the cost savings from the rebates and tax credits to be passed on to the city.

The city will buy the power produced by the system at $416 per month for six years. It will then buy the whole system for about $10,000. The money comes out of the building's operating budget.

The solar energy project isn't Woodbury's first venture in finding ways to apply alternative energy. The solar panel array sits amid the Public Safety Building's green roof, which is covered with thick green vegetation to absorb rainwater, provide insulation and keep the building cooler in summer months.

In 2009, the city undertook a major retrofitting of the mechanical systems at Bielenberg Sports Center, including switching its refrigeration system for the ice sheets to a geothermal system that transfers the Earth's energy to the building. That slashed natural gas and electrical costs by an estimated $100,000 a year.

The city's 2007 renovation and expansion of City Hall also provided energy-saving features that include a green roof, geothermal heating and cooling, energy-efficient lighting and passive solar energy.

The geothermal project at Bielenberg was done on a large scale, Klatt said, and has had a dramatic impact on the budget in terms of reducing natural gas and electrical costs.

The solar panels and other small-scale energy saving steps also serve as valuable demonstration projects. They bring the city a relatively modest cost savings in the context of its $62 million budget, Klatt said, but "everything that we can do helps."

Jim Anderson • 651-925-5039 Twitter: @StribJAnderson