Icy roof stops solar snow sweeper in his tracks

icy-snow-solar-systemeditors-blog-entry3Solar Dweeb 3, Snow and Ice 1. That’s the new score in my ongoing quest to keep our 5.59 kW solar system producing following a snowfall.

It was 3-0, me — until today. About two inches of snow fell yesterday (Jan. 31) here in the Denver area. In other words, not very much. Unfortunately, a layer of ice fell before things turned to snow.

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The previous three times I’ve been up on our roof clearing the lower of two, 13-panel arrays we have, I never once felt there was any real risk of me slipping or falling. The traction was very good to excellent.

Not this morning. As soon as I got up off the ladder and onto the roof, I knew I was in trouble. I started slipping downward right away.

Stranded on a snowy, icy roof
Time to sit on my ass, literally. My cotton sweatpants didn’t slide, but boy, was it cold. This despite, yes, the bright sun that was shining at about 9 a.m. when I climbed up our ladder and onto our roof. That’s because at the time it was 10 degrees below zero (Fahrenheit), and -23 F with the wind chill.

For a few minutes, I sat there on our snow roof like a stranded cat. Then, I decided I had to make it to the ladder, which was about three feet below me.

Luckily, I made it without sliding off the roof. But it’s certainly possible that I might not have succeeded.

The drop to our driveway is no more than 10 feet, and I would have gone feet first — if I’d gone over the edge.

10-foot drop to driveway
I’m not saying I wouldn’t hurt myself — I certainly could have — if I had skeetched over the edge. But there’s also a decent chance I would have landed on my feet and been OK.

I wouldn’t be clambering up onto our roof in snowy conditions if the drop to the ground was 15, 20 or more feet.

All in all, it was a bit of a wake up call.

snow-solar-panels2Next time, I’ll get a long extender and try to do everything from the ground. Of course, this would be hard, given the low pitch of our roof (19 degrees). In fact, our roof pitch is precisely the problem: Snow never slides off of our panels. We’ve got to wait until it actually melts.

Or — if I go up again — and I probably will, I will never go up when I know there’s a layer of ice under the snow.

At this point, I know a lot of you are going to say it isn’t worth it. Just let the snow melt on its own.

On a certain level you’re right: It’s not worth a broken bone or neck to generate extra kWh.

Snow really cuts into production
On the other hand, I think a lot of people think that the amount of production you’ll lose if you let the snow sit until it melts is essentially nothing.

Not necessarily. Depending on your specific situation — weather, roof pitch, system size, outdoor temperature, etc. — you could lose a lot of production by letting snow sit on your home solar system.

Today, we lost about 15 kWh of production due to snow. Thanks to the previous three times I have brushed snow of our system this winter, we’ve saved 40 kWh overall. But we’ve also lost 40 kWh — because I cannot sweep snow off our upper solar array safely.

If I hadn’t swept snow off at all, we’d be looking at about 100 kWh of lost production this winter so far — and I’m guessing we’ll lose another 15 kWh or so tomorrow. And that’s after four snowfalls, three of them of two inches or less.

Add another four snow falls in with similar weather conditions following the snow — typically bright, blue sky, cold weather here on Colorado’s Front Range, and we’re talking about 200 kWh lost if we let our snow sit and melt on its own. Add in four more snow falls, and you’re pushing a month’s worth of electricity — 300 kWh — for us (yes, we’re still pre-electric car here).

400,000 lost kWh?
Let’s do the bigger picture math on this. There are about 6,000 home solar systems along Colorado’s Front Range. Let’s assume they average about 4 kWh in size, and let’s assume that about two-thirds, or 4,000, face similar roof and snow conditions to ours (yes, I know that’s a very rough assumption).

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Let’s then assume eight snowfalls followed by bright, blue-sky but cold weather for several days, or a melt time of about three days for each of those eight snowfalls. Finally, let’s assume , conservatively, about 100 kWh of lost snow production for each of those 4,000 solar systems. That’s 400,000 kWh, or enough to power 50 homes (8,000 kWh per year) for a full year.

That’s a pretty significant hit to solar production. And Colorado’s Front Range (which stretches from Fort Collins in the north to Pueblo in the south and includes about 2.5 million people) is only getting started in terms of a burgeoning solar revolution. As the number of solar systems goes up, so too will the loss incurred by sitting snow.

Do we want 4,000 home owners breaking necks to generate 400,000 kWh? No.

But, given the significant amount of electricity production literally being frozen out by snow-covered panels, I’m not so sure we want to let the snow sit either.


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

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)

(Lost 40 kWh Feb. 1-2, 2011)

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