Do Solar Panels make a Heated Roof Unheated?

[waytsh]

Curious how you guys have been handling this. I am running into situations where I am being asked to review existing buildings for an additional dead load from solar panels attached to the standing seam roof by S-5 clips and a rail system. In some cases the building was considered heated for the original design. When solar panels are installed and they cover a significant amount of the roof I have been considering the roof to be unheated since the panels are usually off the roof by 6" or more. On the other hand I have been told that photovoltaic panels generate heat when in operation. Is it too conservative to consider the roof unheated? Is there any standard which addresses this condition?

Thanks

 

[ARLORD]

If you are refering to heated in reference to snow loads,Ct factor the heated is refering to the internal building being heated vs. unheated interior.

 

[JStephen]

"On the other hand I have been told that photovoltaic panels generate heat when in operation." They're not in operation when they're covered in snow, are they? Your approach sounds reasonable to me.

 

[SLTA]

I agree with ARLORD - the factor is whether the space immediately under the roof is conditioned space, not whether sun hits it directly or not. There would have to be a lot more consideration of shadow lines if it were based on the exterior.

Look at ASCE 7-05 Table 7-3 (p.93) for an explanation of the Ct factor.

 

[PMR06]

I think what waytsh is considering is the idea that the solar panel becomes a large area with unheated space below it (the gap between panel and roofing). For the snow on the solar panel, Ct could be 1.2 instead of 1.0 or 1.1.

 

[waytsh]

That is correct PMR06. Even though the original roof of the building would still be considered "heated" the solar panels have now essentially become the new roof surface and since they are separated by an unheated space should the snow load on the panels be calculated as an unheated condition thereby causing the snow load on the building to increase?

I am no expert on solar panels so take this with a grain of salt but I have been told that they can operate with quite a bit of snow on them. However, their efficiency is greatly reduced. This probably varies from manufacturer to manufacturer and between models.

 

[SteelPE]

I no expert either.... but would panels in areas with large snow loads be at a large incline. I remember hearing that the angle of the panel should about equal the latitude of the project side. Therefore, you may be able to reduce the snow load for the fact that you now have a slippery surface.

Just a thought.