What happens when there is snow on your solar panels?

It doesn't take very much snow to curtail your electricity production. Here's wha† to know when the flakes start to fly.

Photo of a girl clearing snow off solar panels
Cleaning snow off solar panels / 10:10 Climate Action (CC BY 2.0)

I live in Buffalo, a city known for chicken wings and wicked snowstorms.

Despite my city’s reputation for snow, much of the year is great for solar production. Still, I can expect to lose at least a couple weeks of energy production in the middle of each winter due to snow collecting on my panels and blocking out sunlight.

It doesn’t take much snow to curtail electricity production. If there’s just a light dusting, there might be enough residual heat energy in the glass to melt the snow. But any more than that and the snow starts to stick around. I might continue to generate a little electricity, but once there’s about half an inch of snow on top, my solar panels will stop producing any power.

What your solar electricity production will look like in the snow

I don’t have a good view of my solar panels from the ground so I can’t show a photo of what the panels actually look like, but this was my electricity production on a day when my panels were almost completely covered by snow:

Electricity production with snow-covered solar panels
Electricity production with snow-covered solar panels

(The first number on the left is electricity production that day, the middle number is the day before, and the third is the same day last year.)

As you can see in the figures above the graph, I had quite a bit more production the day before. But it snowed overnight, and you can see the impact: my entire array generated a measly 2 kWh all day. While it was overcast that day, the next couple days had a few moments of bright sun but production remained low.

It wasn’t zero: often snow will slump down off the top row of panels, exposing a few solar cells to sunlight. But the array was more or less covered in snow.

For comparison, I went back a couple years until I found a clear day the same week. Here’s what that looks like:

Electricity production on a sunny winter day
Electricity production on a sunny winter day.

The days here get pretty short in winter, so that’s about as good a day as I can expect. If those panels were covered in snow, I would have lost nearly all of that production.

Do solar panels melt snow?

Solar panels don’t generate heat, so snow isn’t going to melt off them very much faster than the air temperature allows.

However, they are dark colored and passively absorb energy from the sun, making them a little bit warmer. This is sometimes enough heat to help clear the panels if there’s only a light dusting of snow, but in my experience this small amount of heat can’t be relied on to keep your panels clear of snow.

How does roof slope help keep your solar panels clear?

Snow is surprisingly sticky, especially if it’s a wet rather than a dry, powdery snow. My roof pitch is 5:12, which is a 42° angle. That’s pretty steep. Even so, the snow doesn’t really slump off until the temperature warms up.

I have another thing working against me, which is that the bottom row of my panels is mounted on a flat section of roof that abuts the pitched section. That’s a recent addition to my home. Before that addition, if I had a few inches of snow on my panels, the snow would slide off the roof once the temperature warmed up a little.

This would sometimes happen in dramatic fashion: the snow would slide off like an avalanche. This is something to keep in mind if you have solar panels on a pitched roof. Be prepared for avalanches off your solar array to happen, so you might want to keep the area underneath clear of things like patio furniture or vehicles.

If you have a roof with a very steep pitch, you probably will have better luck with clean panels in the winter. Conversely, a flat roof will remain snow covered for longer.

When does snow melt off your solar panels?

There are a couple ways that snow will clear off your solar panels.

The first is wind. If it’s very windy, even an inch or so of snow will blow off them. But in my experience, wind isn’t very reliable for keeping your panels clean if you have more than an inch or two.

The other way that panels get cleaned of snow is melting. Once the temperature nears 32°F, the snow will start to soften and slide off.

Should I manually clean the snow off my solar panels?

This is when having ground-mounted solar panels is a big advantage. If there is snow, use a soft tool to gently brush it off. A broom or car snow brush would work well.

However, if you need to climb on a slippery aluminum ladder to reach your panels, I would say that it’s not worth the risk. The hospital bill that could possibly result would far outweigh the few dollars in extra electricity generation you might get. So, please, use your judgement.

If your roofline is low and you think you can safely reach your panels, you can use a snow rake like one listed in the Amazon ad below. Be sure to choose one with a plastic head! Swinging a metal rake against your glass-faced solar panels is certain to cause damage.

How much money will I lose from having snow-covered solar panels?

I pay about $0.14 per kWh for electricity with full net metering in New York. The difference in my power generation between that sunny day in 2019 and the cloudy, snow-covered day on January 11 this year was 15 kWh, which works out to $2.10 of lost electricity that day (if it was sunny instead of cloudy).

However, most winter days in Buffalo are pretty overcast. Even with clean panels, I might generate only a few kWh per day.

I would guess in total I lose about three weeks a year of electricity production because of snow covered panels. Let’s say the average day is only half sunny. This means I would generate 8.5 kWh a day on average (half of my sunny day example). Over 21 days, that would be 178.5 kWh, or about $25 worth of electricity.

That’s not nothing, but it’s also not enough for me to worry very much about.

Estimating your electricity losses due to snow cover

If you haven’t had solar panels during the winter and you want to estimate how much electricity generation might lose because of snow, you can use the The Solar Nerd calculator. Enter the details for your home, and scroll toward the bottom of the report. You’ll see a chart that estimates your electricity generation each month of the year.

Think of how much snow you typically get, and make an educated guess of how many weeks of electricity production you might lose in a winter. The chart from the calculator will give you an estimate of how much electricity you might generate in the winter months. Based on that, you can estimate your electricity losses.

Once you do the math, you’ll probably find that it’s not worth worrying about.

Bottom line: don’t worry too much about snow

If you’re lucky and have a ground-mounted array, go ahead and grab a soft snow brush and keep your panels clear after a snowstorm. Being able to keep your solar panels clean is one of the advantages of having your solar panels within easy reach.

Most homeowners have their solar panels mounted on the roof. In this situation, it’s probably not worth worrying when the snowflakes start to fall.

If you want to look at a real world example, feel free to explore the public data for my solar panels.

For further reading, we also have an article comparing solar power generation between summer and winter.

TAGS:
#Homeownership #Weather

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