Yes, snow on solar panels does matter


editors-blog-entry3Snow has affected our solar production much more than I expected it would in our first winter with a 5.59 kW solar system on our Aurora, Colo. rooftop.

No one, including solar companies, has really paid much attention to the issue of snow on solar panels. The conventional wisdom – which, by the way, in our case is just plain wrong – is that snow slides quickly off of panels in sunny conditions.

The lack of attention to the issue of snow on solar panels and the misinformation about it is a primary reason I’ve been writing about our own experience with snow on solar panels this winter. Call ours a case study in snow on a central-inverter, string-based solar system during a Colorado winter.

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Case study in snow on solar panels
As a participant observer in this case study, I’m very definitely learning as I go along. Among the things I’ve learned so far:

  • If your roof pitch is below 30 degrees, snow probably won’t slide off panels very quickly; it’ll take days to melt — even in 100 percent sunny conditions;
  • At least in Colorado, where snowfalls are often followed by cold, sunny days, you can lose a lot of production to snow if you let it sit until it melts;
  • It can be very difficult, if not impossible, to remove snow from one’s solar system, depending on your specific solar set-up;
  • The 23-foot Mr. Longarm is a decent solution to helping us clear part of our solar system, but I can only reach half of our system with it – and I have to climb up a ladder in order to do so;
  • It might have been a good idea to design our 5.59 kW system differently so that we could have easier access to the upper of two 13-panel strings;
  • Micro-inverters may be a very good idea in snowy climates;
  • Tigo Energy module maximizers, which, like micro-inverters get around the frankly ridiculous production limitations of a central inverter system which mean a single low producing panel brings an entire string to a grinding halt, are another good option for those in snowy climates;
  • Yes, snow IS a shading issue – a very big one, and one I believe solar companies tend to pay insufficient attention to;

Learning as we go
I learned a couple of new things after our most recent snowfall:

  • Watch your weather forecast closely and frequently;
  • If you’re going to brush snow off your system, don’t wait too long – or it might turn to ice;

mr-longarm-roofI decided not to sweep about one inch of snow off our lower 13-panel array Monday morning because the forecast I’d read online the night before indicated it was going to snow all day on Monday.

It didn’t snow at all on Monday during the day. It was cloudy, but I estimate that we still would have produced about 10 kWh from our lower array if I’d swept it on Monday morning before I went to work.

I let the one inch of snow sit, assuming more would fall, which, again, it did not. And the snow turned to a crust of ice, which I could not sweep away with the Mr. Longarm this morning.

Lost kWh
Today is another cloudy day here on Colorado’s Front Range (the sun is sometimes breaking through), with some minor flurries, none producing any measurable accumulation.

So, I estimate we could have produced another 10 kWh today from our lower string, had I swept it on Monday morning. That’s 20 kWh lost because I failed to re-check the weather forecast on Monday morning and did not sweep the snow off our lower 13-panel string at that time.

Yes, I know 20 kwh isn’t a huge amount, but it is 2 ½ days worth of electricity use in our still pre-EV home. It’s also about 80 miles of EV driving, or the equivalent of 3 ½ gallons of gasoline not burned if those 20 kWh were to be used to power an EV.

Snow on solar panels does matter
Our kWh lost to snow are starting to add up, as you can see by the table at the end of this entry. Multiply our loss by tens of thousands of solar systems, and it the lost kWh are much higher — in the hundreds of thousands of kWh, possibly millions, in the U.S..

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Yes, snow on solar systems does matter!

Thankfully, someone is finally starting to take snow on solar panels seriously. Researchers at St. Lawrence College and Queen’s University in Ontario have conducted a preliminary pilot study on snow and solar panels. They’re planning to use the results as a guide to conduct a more extensive and rigorous study.

As Adegboyega Babasola, lead researcher at St. Lawrence College’s Sustainable Energy Applied Research Centre, notes, “There have been very few comprehensive studies performed which attempt to quantify the effects of snowfall, and none which provide universally applicable estimations of snow-related losses.”

Sweeping the snow off solar – An ongoing tally of kWh gained & lost

Snowfall date(s)

Snowfall Amount

Date and time of snow sweeping (lower of 2 13-panel strings of 5.59 kW system only)

Estimated kWh gained from sweeping (gain may have been across multiple dates)

Dec. 30-31, 2010

2 ½ inches

Jan. 1, 2011
12:30 p.m.

7.3 kWh

Jan. 9-10, 2011

6 inches

Jan. 10, 2011, 8:30 a.m.

33 kWh

Jan 19, 2011

1 inch

Jan. 20, 8:15 a.m.

6 kWh

Jan. 31, 2011

2 inches

Feb. 1, 9 a.m. (roof too icy; failed to sweep much snow off)

0 kWh (failed snow clearing attempt due to icy roof conditions)

Feb. 5-6, 2011

5 inches

Feb. 6, 9 a.m. (from ladder with 23′ Mr. Longarm)

13 kWh

Feb. 7-8, 2011

6 inches

Feb. 9, 8 a.m. (from ladder with 23′ Mr. Longarm)

29 kWh

(12 kWh of additional production missed on 1st day due to slivers of snow left on on few panels — minuses of central inverter system)

March 6-8, 2011

1 inch

March 8, 8 a.m. (from ladder with 23′ Mr. Longarm)

0 kWh

(waited too long to sweep snow away and it turned to ice, which was unsweepable)

Running total kWh saved as a result of sweeping snow off 13-panel garage roof string

88 kWh

Running total kWh lost as a result of not sweeping snow off 13-panel upper roof string

108 kWh

Running total of additional kWh lost as a result of limitations of central inverter system

20 kWh

Running total of estimated kWh that could have been produced with immediate, 100-percent post-storm clearing of snow from entire 5.59 kW system

216 kWh

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