Snow loads on PV arrays

[silverhorsefarm]

This last February, we in Maryland received a pair of back-to-back storms that left a record-breaking 40 inches of snow on the ground and on roofs.

What has been the experience with snow on large PV arrays? Do they tend to stay warm enough to melt or slough off large snow loads, or should I go shopping for a snow rake?

[Mike90250]

I think in the fine print, along with the hail stone impact test, mfg's list the snow load.

Further north, you need higher angles, for better harvest, and so that tends to shed snow more.

A problem, is the panel acting as a dam, and hindering the snow sliding off the roof. Or a wedge of snow sliding down, and smashing into your panels. Ouch!

[silverhorsefarm]

No obstruction - it's a perfectly flat roof with a typical pitch angle. But February's snow were wet enough that the loads stayed up there until they melted. i was hoping the panels would improve that situation.

[Mike90250]

Some light makes it thru the snow, and actually powers the panels, which being navy blue, heat up. But if not sloped enough, to slide the snow off, it re-freezes each night.

[ionized]

Added weight of the panels + big snow storms means a lot of extra weight. You better get the engineering right or you could have a collapse. Most homes in the NYS snow belt that I grew up in rarely had snow sliding off of them. Metal roofs on sheds and barns, yes. Homes with shingle roofs, no. The panels would tend to shed it and let it pile up in between, I suppose.

Snow can raked off shingle roofs standing on the ground if you have a long handle on the "rake" and the home is single story. Lots of people do it in unusual snow conditions. Panels will make that difficult too.

[dave]

A case for a tracker

One of the reasons that I am going for a solar tracker is because of snow / wind loads. I have a pitched roof with a 60 lbs per square foot snow load. Snow rakes are good if you want to stay up all night pulling each foot of wet snow off as it accumulates. With a properly designed tracker the snow or wind load can trigger the unit to dump snow off the roof or duck behind the peak to avoid the wind. It does not have to be a complicated design - you just have to have the reliability of the equipment with backup alarms if the mechanics fail = a reliable manual method. Although the trackers on the internet "look cool" they all appear to have their flaws. A pitch roof is a fairly fragile environment for most fixed trackers in a northern environment. I think that there is a long way to go design-wise for a good tracking system to withstand the environment. I have come up with some ideas for improvements and will be building a first try setup this June. It has the above two criteria and will be a small 1kw system - but at least the third criteria - being able to add a similar unit right next to the original - on the other side of the peak. The materials cost considerably more for fire and lightning protection then they do for tracking so at least I will have a roof over me at the end of the day!

[ed2kayak]

Februray Storm South Central PA

What is roof pitch, mine is 30 degrees and snow was gone in 3 days.
Or maybe roof rake, wouldn't work for me. But you could probably use stepladder.

http://news.cnet.com/8301-11128_3-10156471-54.html

I couldn't get pics from here uploaded for the Feb storm. But 2 days after, snow was 1/2 gone. 3 days after it was all gone.

I'll try pics again later.

[ed2kayak]

December 2009 Storm

Had 8 inch snow in December, didn't last the day. Pics in my album.

http://www.solarpaneltalk.com/album.php?albumid=28

[ed2kayak]

February Storm

I stopped measuring after 24 inches, so I don't know what the official storm total was here. Plus near blizzard condition had the storm drifting quit a bit.
Pics are 2 & 3 days after.

[Jarod]

The solar panel can hold a press nearly 5000 Pa, likes half meter of water cover the solar panel, for snow, it's likely 1 meter for melting snow and less than 2 meters of soft snow. 40-80 inches of snow~~ than will be really heavy snow~~