To sweep your home solar system or not to?

Christof Demont-Heinrich
Musings on going solar

snow-solar-panels2editors-blog-entry3Is it worth it to brush snow off of your home solar system?

The answer depends on a number of different factors, including, but necessarily limited to:

  • How much snow;
  • How cold it is, or will be, and for how long;
  • How cloudy it is, or will be, and for how long;
  • How accessible your roof is and your roof’s pitch;
  • Safety – how dangerous is it for you to sweep snow off of your system?

As I noted in a previous entry on this topic, my inclination in terms of our own 5.59 kW system here on Colorado’s Front Range is that it is generally worth it to brush snow off of our solar system.

That’s why, after a moderate snow that began on Thursday afternoon (Dec. 31, 2010) and which fell through the day on Friday, I climbed onto our roof on Saturday at about 12:30 p.m. and brushed the snow off of the lower, 13-panel array that’s installed on our garage roof, and which comprises one of the two arrays on our 5.59 kW system.

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

Snowfall date(s)

Snowfall Amount

Date and time of snow sweeping (lower of 2 arrays 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

???

???

???

???

I can’t get to our upper array very easily, which, thanks to the lower array, requires shimmying along a roof edge with just enough room for your feet (see picture above). It simply isn’t safe to do this in the winter, although I have done it on a number of occasions in dry, warmer conditions so that I could wash down the upper array.

There is a definite risk every time anyone climbs onto a rooftop. However, as rooftops go, ours, especially the part that sits over our garage , which is attached to our home, is fairly benign. The pitch is only 19%. So, even in snowy conditions, the chances that you’ll fall off are extremely low — if you’re careful.

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Powdery snow doesn’t cling
We didn’t get that much snow — maybe 2 ½ to 3 inches of pure, powdery white stuff that didn’t cling to the panels at all when I brushed it off with a terri cloth mop I had duct-taped to an extender pole (the pole I got courtesy of our neighbor, who owns a landscaping business).

It was cold on Saturday – we had a high of about 25 degrees Fahrenheit, and it was mostly cloudy, but with moderate sun beginning to make its way through high-level cloud-cover. I knew the snow wouldn’t melt by itself for about two days, and I wanted to minimize the kWh we’d lose.

So, up I went on our ladder.

Was it worth it?

Snow-sweeping nets 7.3 kWh
Well, with half of our 5.59 kW system operating for about three good hours of sun on a mostly cloudy day Saturday, we managed 1.8 kWh in the afternoon.

Today, Sunday, was a different story. It took until 1:30 p.m. for any snow at all to melt off the upper-roof array, which I could not clear on Saturday. And, by the end of today – which saw about 4 hours of cloudy weather and 2 ½ hours of bright sunshine, and a of about 38 degrees here in Aurora, Colo., — about 60% of the upper array of 13 panels was still covered in snow.

Meanwhile, the lower array – which I had swept free of snow on Saturday – produced about 5.5 kWh before the upper array began kicking in a little bit of electricity.

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Moderate, but tangible kWh payoff
So, sweeping the snow off the part of our 5.59 kW system the I could reach in reasonable safety, netted us about 7.3 kWh of electricity. Meanwhile, we lost about 7 kWh of electricity because I could not reach the upper array to sweep it off.

A bit over 7 kWh isn’t a ton of electricity. But it’ll yield about 28 miles in an EV, or about 1 ½ loads of laundry in our dryer.

I’m going to start keeping track of the kWh that sweeping snow off our lower array generates during the next four or five months (yes, it does snow on the Front Range in May, though usually only once or twice), and see what the extra effort and, yes, extra risk – it truly is a small risk, given our roof situation, and my conservativeness when I’m up there – yields in total.

Stay tuned 🙂

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