Minnesota energy pioneers are learning the quirks of solar panels.
President and Founder of tenKsolar, Dallas Meyer, talked about how how the tenKsolar company solar arrays were designed to work in snow conditions, like those encountered in Minnesota. The solar arrays were mounted on the roof of the Bloomington company headquarters.
One night last winter, just as they settled down to sleep, Andy and Sara Kubiak of Lakeland Shores, Minn., got jolted back to reality by a loud "kaboom."
"Maybe it's an intruder," Andy Kubiak recalled thinking.
It turned out that the Kubiaks had just been taught a lesson about their rooftop solar-power array. Snow can build up on solar panels and, with luck, it slides off -- sometimes noisily.
"It was an avalanche," Kubiak said.
With more than 700 solar arrays now operating in Minnesota, a growing number of energy pioneers are learning the quirks of extracting electricity from the sun in a cold, snowy place whose short winter days bring added gloom from lost kilowatt hours.
One question that owners of solar panels often hear is: Do they work in the winter?
"I've probably been asked 100 times," said Mike Greenbaum, finance and development director for the Merrick Inc., a nonprofit that installed solar panels atop its Vadnais Heights headquarters in 2008.
The answer, he and others say, is yes. Cold turns out to be good for solar power. Snow can be bad, but this year's mild winter has helped keep the juice flowing.
Heavy snows, like the blast that collapsed the Metrodome roof last winter, can cut output dramatically, sometimes to zero. On many arrays, a quirk of the design can halt all electricity production if a portion of the panels is snow-covered, owners say.
"There was a whole week last year when we got dumped with snow and not a single kilowatt was produced from our solar panels," said Seth Nesselhuf of Quality Bicycle Parts, which installed a solar array on its Bloomington headquarters in 2008.
To rake or not to rake?
Big snowfalls present a dilemma to solar pioneers: Is it worth the hassle of clearing the panels to restore output?
At Spruce Tree Centre in St. Paul, property manager Jason Sklar has climbed onto the roof three times during winter since the office building installed its solar array in 2009. He brushes off the snow by hand to avoid damaging the glass surface.
"It is part of normal maintenance," said Sklar, who hasn't had to clear the array this winter. "It's not a hassle at all."
Others, including Merrick and Quality Bicycle Parts, skip the rooftop snow removal and just do without the solar power, relying on their utility, Xcel Energy, instead.
Some homeowners, including the Kubiaks, have purchased long-handled snow rakes with a foam edge to carefully brush away snow from rooftop arrays.
"It's very difficult to use, and I am always nervous that I am going to scratch the glass," said Andy Kubiak, who plans to rake only after the worst snowstorms. "I am just trying to get rid of the bulk, rather than be shut down for days."
Jacò Botha also bought a snow rake to clear the solar panels on his Eagan home. A scientist by training, he calculated that to recoup the $180 he spent on the rake, it would take five winters of raking, assuming he annually saved two weeks of otherwise lost power output.
"It is a lot of work, and if you have a two-story house like I have, you spend a lot of time out in the cold at the end of a very long pole," Botha said. "The conclusion I made after the second winter is that it's not worth the effort."
Another option is to avoid rooftop solar arrays. Engineer Craig Tarr, founder of Energy Concepts in Hudson, Wis., said about half the solar power systems he designs are at ground level, mounted on poles and easily cleared of snow.
Panel angles and cold
Minnesota gets less than 1 percent of its power from solar, but its contribution is growing. Two large-scale solar arrays to be built this year atop the Ikea store in Bloomington and in a field outside Slayton, Minn., will boost the state's total solar output above 6 megawatts.
That's only the equivalent of three or four wind turbines. But unlike wind power, solar electricity can be more dependable on sunny summer days -- which is when electricity demand typically peaks. In winter, when solar output ebbs, so does demand, experts say.
Getting power from sun rays, whether summer or winter, is partly a question of angles.
Ideally, said Tarr, a solar panel should be at nearly a 45-degree angle. That captures sun rays well, and gives enough slope for snow to slide off most of the time, he said.
But other factors can dictate how solar panels are mounted. The steeper the angle, the more building strength is needed to prevent the panels from becoming roof-ripping sails during windstorms, he said.
Merrick's panels have a relatively low slant to reduce storm risk, said Tarr, who designed the system. That's not helpful in shedding snow, but the low angle can improve output during key hours of summer days.
One wintertime shortcoming of many solar panels, according to Tarr and others, is that solar cells typically are wired in series, much like strings of Christmas lights that go out when one bulb is lost. On such solar panels, snow covering just a few cells can disrupt the output of the entire array.
That issue was avoided by TenKsolar, a Bloomington-based panel maker. It wires its solar modules differently, mainly to enhance performance and capture reflected light, but with important benefits in the winter.
"We can have basically an array that is half snow-covered and still get half the energy off the array," said TenKsolar founder Dallas Meyer. "The panel is not dependent on all the individual cells being uncovered."
Meyer also said that solar panels warm up as they generate power, which helps to shed any lingering snow. He said panels atop the TenKsolar building usually clear themselves in a day or two after a snowfall.
Perhaps the biggest surprise for solar newbies is the effect of low temperature.
"Cold -- it's actually good," said Meyer.
Some solar panel owners said they've seen output increase when the temperature turns cold, but the days stay sunny. The reason, said Meyer and others, is that solar cells' voltage drops when temperature rises.
That benefit can't offset Minnesota's basic problem with winter sun: There's just not enough of it.
For example, the output of the solar array at St. John's Abbey in Collegeville, Minn., peaked last year in July, when daylight typically lasts 14 hours. In the shorter days of December, the output dropped -- by nearly three-fourths.
David Shaffer • 612-673-7090