Snow Accumulation Around Roof Mounted Solar Panels

[SkiisAndBikes]

It is becoming increasingly popular to install arrays of solar panels onto existing flat roof structures. See attached jpg for an example of racking for solar panels.

The racking and solar panels are elevated from the top surface of the roof and racking manufacturers typically provide leg loads due to wind/snow/dead loads. I am interested in finding out more information/opinions on the effect the solar panel installation will have on changes in snow accumulation and drifting on the roof itself. I would presume that there would be some form of additional snow accumulation due to aerodynamic shading, however, I have not been able to find any recent studies or publications to help quantify. In asking around, there seems to be an undocumented opinion in the industry that there will be no net increase in snow loading on the roof.

 

[ajh1]

Here's an older research report on the subject.

 

[SkiisAndBikes]

ajh1,

Thanks ajh1 for the link to the report! It is along the lines of the others that I have found, which are also of similar vintage. I am still going to search for more current published research and am still interested in any other opinions on the effects of drifting around solar panel installations.

 

[gander1]

Have you been able to locate newer facts regarding snowload and windrifts around solar panels on flat roofs? Attached is a system we are considering. It is non ballast and we are told will allow wind some wind scouring. We plan to use in Ontario. I would appreciate any leads you can give me.

 

[SkiisAndBikes]

Gander,

I have not been able to locate any newer research, although I understand RWDI might be producing some more research soon. After looking at your photo, my opinion (not backed by research), is that such a system installed low to the roof would result in aerodynamic shading which can result in additional localized snow drift accumulation not originally envisioned when the roof structure was originally designed.

 

[Brad805]

I would hope the owner might employ a program to remove the drifts. Snow covered solar panels are quite useless.

Brad

 

[SteelPE]

I find this whole thing to be a PITA.

I had a client that was looking to install a system on a new roof. Initially I was told not to worry about it as the panels would be laid flat. Then they decided to go with a system similar to photo presented by gander1. Complicating this was the fact that they system would be self ballasted in a 120mph hurricane zone and system would be in an area with relatively large snow loads.

Nobody wanted to help me figure out what was going on. I contacted the solar panel mount supplier only to be told they would provide me the information (something they had done studies on) only after they were awarded the job by the client. Kind of like the chicken and the egg. I needed to design the roof to get the job through the planning phase but they wouldn't tell me what to design it for.

I imagine if there wasn't a big "green energy" push going on right now they would have bent over backwards to get their foot in the door. Since they were to busy to help us I told the client to go forget their system and go in a different direction. I imagine they couldn't really care less.

 

[SkiisAndBikes]

PITA for sure, especially retrofit's. At least for new construction you can design the roof assuming additional snow accumulation. IMO there is no way that you can rely on an Owner to remove the drifts. Generally, snow will slide off the solar panels, depending on angle, within a day or two. However, that is not my concern, the additional drifting of snow around all the racking due to aerodynamic shading should be considered, similar to drifting against parapets, mech penthouses, and similar projections.

I pretty much am passing on all future retrofit programs until more research/guidance is available, although I keep seeing them continue to be installed on rooftops, seemingly without any strengthening.