Snow on solar panels? Here’s why you shouldn’t panic

Snow on solar panels? Here’s why you shouldn’t panic

November 2, 2021 Uncategorized 0
Snow on solar panels | Wolf Track Energy

Winter is coming. You may not like it, but soon you’ll be seeing the white stuff everywhere. Yes: there will be snow on solar panels. 

If you have a rooftop system that’s hard to reach, this might seem like a headache. After all, solar panels can only generate electricity when the sun is shining on them. 

And rest assured: You will find snow on solar panels in the Duluth region during the upcoming winter months. The Zenith City sees plenty of heavy snowfall, about seven feet of it per year, according to the National Weather Service.

But how big of a deal is a snowstorm? As we’ll lay out in this blog, it shouldn’t make a big dent in your annual production. In other words, it’s not a dealbreaker for people considering going solar.

So climb down from that ladder and read this blog.

Burning daylight

Snow cover isn’t the only thing working against solar production during the winter. The sun is out less, providing less time for solar systems to soak up those precious rays. 

In the solar industry, we use kWh/square meter/day as a measure of how much solar energy a given place receives. In Duluth, we receive 2.06 kWh/square meter/day in December, while July provides more than three times that amount of sunlight. 

So before we even account for snow, solar systems in Duluth are already producing less electricity due to reduced sunlight. 

Ground mount solar panel array | Wolf Track Energy

Using the default settings for a system in Duluth, PVWatts says December will only account for 4% of my annual solar production. That means a given December day will only account for about .1% of my annual solar production. 

What does this mean for snow on solar panels? Say there’s a big December storm that covers my panels, totally eliminating their solar production while the snow sits on top of them. If the snow stays there for a week, it would still mean I’m losing less than 1% of annual solar production. 

But as the U.S. Department of Energy points out, a light cover of snow shouldn’t affect solar production because “wind can easily blow it off” and “light is able to forward scatter through a sparse coating.” Heavy snow is where we start to see problems. 

Even that snow should come off on its own within a few days, a University of Minnesota expert told WCCO last year. However, roof pitch can affect how long the melt will take. A steep roof may see snow slide off more quickly than flatter ones.

Wiring panels

The way solar panels are wired and orientated could also affect how much energy is lost due to snow cover.

Previously, we talked about inverters, an important device that converts the electricity produced by your panels into electricity you can use in your home. One common way solar systems have been wired is to use a centralized “string” inverter that essentially converts electricity produced by a group of panels.

But it’s becoming increasingly common to see “microinverters,” which make that conversion at each individual panel. Similarly, string inverter systems can be paired with “optimizers,” which monitor each panel’s performance and improve their output.

Systems with microinverters or optimizers are better suited to handle snow cover. Why? Because a “string inverter system can only perform as well as its lowest-performing panel,” according to inverter manufacturer Enphase. So if snow is covering just one panel in your traditional string inverter system, it would have a bigger impact than if you had microinverters or optimizers.

Bypass diodes

Now that we’ve talked about different ways to wire solar panels on a system-wide level, let’s talk about the circuitry inside the panels and break down “bypass diodes.”

A diode is essentially an electrical check valve that only allows current to flow in one direction. In solar systems, they allow current to bypass panels or sections of panels that are affected by tree shade and other factors that affect production. Essentially, it allows current to flow around a blocked pipe and optimizes production.

The orientation of the solar panel and the location of the bypass diodes will affect how much energy is lost due to shade. Say a solar panel has three bypass diodes, creating three sections of the panel. We’ll use the illustration below as an example. 

Snow on solar panels | Wolf Track Energy

If the above panel is installed with a landscape orientation and the snow is sitting on the bottom third of the panel, then you’ll lose energy from that one section. But if the panel is installed with a portrait orientation, you could lose energy from those three sections, since they each see some snow cover. 

Snow on solar panels: What to do?

Enough technical talk. Let’s get back to the issue at hand: what to do about snow on solar panels. 

If you have a rooftop system, it’s probably not worth removing snow from your panels every time it snows, given the low amount of sunlight you’ll see on a winter’s day.

But you could check the weather forecast before taking on that chore. If you’re in for a few cloudy days, you can probably skip it. But an upcoming slate of sunshine could be a perfect time to wipe off the snow. Ideally, you’d use some kind of rubber roof rake that’ll clean off snow without scratching or damaging your panels.

If you have a ground-mount system, it becomes much easier to clean off your panels to squeeze every drop of solar production out of your system.

But again, snow cover shouldn’t be a source of stress when it comes to your solar system, since winter sees much less sunlight to begin with. You’ll make up for it in July. 

Besides, you’ll have plenty of other issues to worry about in the dead of winter, like plowing your driveway and making sure your car will start in the morning. Aren’t you excited for winter already?

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