Winter, snow, and solar panels: A mixed forecast

With many people in the U.S. bemoaning the punishing winter weather this year, solar-panel owners have their own special gripe: sun-blocking snow and ice. But at the same time, very cold temperatures have given some owners a power boost.

A thick blanket of snow can slow a solar photovoltaic (PV) array's production to a trickle. That's something I discovered two years ago when a snowy winter led me to buy a modified snow rake to remove snow from my solar panels. It's now on my list of regular winter chores.

Even with my diligence, this year has been particularly tough because of the frequency of the storms and the type of snow. Last week, New England had yet another dump of wet and sticky snow followed by icy rain, which made snow removal tricky.

Patiently letting the sun melt the snow is a perfectly reasonable thing to do, say solar industry professionals. But many people manually remove snow in winter to maximize power output. Solar panels, it turns out, really like cold weather.

At the opposite end of the country in the U.S. Southwest, frigid temperatures last week resulted in fantastically good production. The parents of my colleague Stephen Shankland have three high-end solar panels on their roof which produced just over 14.5 kilowatt-hours one day last week. That's well above the daily average for this time of year and more than my roof-full of 14 panels often does.

With the temperatures in the region not getting above zero all day, the panels generated 2 kilowatt-hours for two hours in the middle of the day, which is extremely rare. It's also a good bang for your buck when you consider many homes have limited roof space with good sun.

Although it may sound counter-intuitive, solar PV panels perform better in cold weather and similarly, performance degrades in high heat. Amy Beaudet, who has a solar array in Massachusetts, calculates that the maximum wattage of her array in Massachusetts is up to 25 percent higher in the winter than in the warmer months.

The technical reason for the power increase is that the voltage of solar panels increases as temperatures go down, said Beaudet who does technical sales at renewable-energy e-commerce outlet AltE Store. The higher voltage (you can think of it as pressure), combined with the same current from the panels as during warm weather, results in higher wattage, she explained.

The tilt of panels also figures in winter versus summer production. People who use solar panels in an off-grid situation typically angle the panels to better take advantage of the winter sun because of the shorter days, she said.

Still learning
Back at my house, snow removal has become a bit of a preoccupation for me on sunny days after it snows. And I'm planning on modifying my roof rake again to better ensure I don't damage the surface.

With my 20-foot snow rake, I can only reach the bottom one third of the panels. So my strategy is to pull away what I can and wait for the sun to do its thing. Once more dark-colored panel is exposed, more current starts flowing and the rest of the panels heat up.

Clumps of snow tend to slide down from the higher panels and I scrape those chunks off as they come. It's not unusual to hear a large thump from sliding snow on sunny days after a snow storm, something I try to remember when I walk beneath them so I don't get clobbered.

The snow rake I bought at my local hardware store is made of aluminum. So to ensure that the hard head does not strike or scratch the solar panels (and generally keep metal away from electricity generation), I screwed on a strip of door weatherstripping to the edge of the rake head, which means that a strip of nylon is gliding along the panels. Now, I'm planning to screw soft pipe wrapping, the kind you insulate hot water heat pipes with, along the edge.

Often, solar-panel owners use some sort of squeegee-like contraption to take snow off, said AltE Store's Beaudet. A friend of mine with newly installed panels bought a snow rake with a plastic head which allows him to push the snow off from inside the house. Another product called the Sno Knife, which has a flat plastic head designed to work in different types of snow, shouldn't damage glass-covered solar panels, according to the company.

The story for solar hot water panels or tubes is very different. The copper inside solar hot water panels gathers heat relatively quickly and the snow tends to melt quickly, Beaudet said.

One technical advance which is helping make shading of solar PV panels less disruptive is microinverters. Traditionally, an array of panels is wired together and connected to a single inverter, a box about the size of a PC that converts the direct current to household alternating current.

One downside of this approach is that if one panel is shaded by leaves or snow, production of the entire string is compromised. Microinverters do the DC-to-AC conversion on each panel so if one panel is blocked, it doesn't affect the others.

Of course, removing snow assumes you can actually get access to a roof. Often, people simply just wait for the sun and wind to do the work for you. And if it's icy, trying to scrape it off is not a great idea, said Beaudet.

In my case, I popped in and out a few times on Friday in an attempt to speed up the melting with an occasional raking. I wanted to avoid a chunk of snow sliding down and freezing in place when the cold weather set in for the night. It worked: by the afternoon, the panels were cleared. Just in time for night fall--and the next forecasted storm.