April snow showers slow down solar production

Tuesday, 05 April 2011 19:38 | Written by Christof Demont-Heinrich, SCD.Com Editor |

editors-blog-entry3 Snow season is winding down here on Colorado’s Front Range, but that doesn’t mean we’re completely done with snow, or that it’s not still affecting our home solar production.

Our snow season has been full of surprises and the two inches of snow which fell on April 3 into April 4 were no exception.

As the snow tapered off on the evening of April 3, I thought about hosing the two inches of snow off our 5.59 kW, 26-panel, two-string system.

Then, I thought, “Nah, tomorrow is supposed to be clear and sunny with temperatures in the 50s – it’ll melt quickly on its own.”

Mistake.

April sun still not enough?
It took five hours for the snow to melt off our system to the point where it was producing meaningful amounts of electricity. This on clear, blue-sky April – yes, April! – Colorado day.

Had I been able to spray most of the snow off the system with our hose Sunday night – a safe assumption, I think, we would have produced about 15 kWh more of electricity than we actually did because I thought April sun conditions would melt the snow more quickly than they did.

Our 15 kWh of lost production now goes onto the “lost to snow” table below.

As you can see from the table, which chronicles one Denver area solar homeowner’s experience with snow, one can indeed lose significant amounts of solar production to snow cover.

Of course, how much you lose is dependent on a fairly large number of factors, with roof pitch, post snowfall weather conditions, and, finally, whether you have a central-inverter based system or not, probably the most significant of these.

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)
March 18, 2011	1/2 inch	March 18, 8 a.m. (from ladder with water hose)	3 kWh
April 3, 2011	2 inches	Did not sweep or hose, thought April sun would melt snow immediately (it didn't)	0 kWh
Running total kWh saved as a result of sweeping snow off 13-panel garage roof string			91 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			235 kWh

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