Solar panels on steel building

[EricF]

Hi guys,
I'm looking to install solar on the roof of my steel building, one thing I'm trying to figure out is how that racking would work. The purlins run horizontally on 5' centers, but most panels are only 64" long. I'm looking to install around 30 panels, likely in 2 rows of 15.

I can't imagine you can support the panels that far apart, can you? If not how do you do it?

Thanks,
Eric

[inetdog]

Hi guys,
I'm looking to install solar on the roof of my steel building, one thing I'm trying to figure out is how that racking would work. The purlins run horizontally on 5' centers, but most panels are only 64" long. I'm looking to install around 30 panels, likely in 2 rows of 15.

I can't imagine you can support the panels that far apart, can you? If not how do you do it?

Thanks,
Eric

You do not support the panels that far apart. The racking will have both horizontal and vertical (parallel to ridge and perpendicular to ridge) elements, and between them you will be able to provide multiple mounting points per panel along their long dimension.
The layer of racking closest to the roof may need to be beefier than normal for that spacing between purlins.

Take your building specs to a company like IronRidge that designs systems at little or no charge as well as providing the parts and see what they recommend.

[EricF]

That is what I expected to hear. Thanks for the info and the link to IronRidge!

-Eric

[solarix]

I've done these. The pitch of the metal roof is very low right? maybe 5deg. You need to tilt the panels up to at least 15 degrees so that they will catch the sun better and self-clean in the rain as well. The back leg is going to need to be about 15" long which allows you to secure it to the back purlin and angle it forward to support the panel near the designated mounting holes. This creates a triangulated mounting which is good and strong. Read the panel manufacture's instructions carefully as to where they will allow support and what span can be done. This varies quite a bit with different PV panel brands. Some have just one set of mounting holes, some have two and allow you to be pretty close to the panel end.

[EricF]

The roof is 2/12 or 10 degrees. According to PVWatts there is a 4% efficiency difference between 10 and 20 degrees and that is small enough I wasn't going to mess with it. I didn't realize the attachment location was that specific on some panels, that is a great tip.

That actually leads me to another question. I'm a handy guy and good with electricity and wiring but of course as with many things there is a learning curve to solar installs. I haven't found a good resource that outlines the most common tricks. I'm sure there are some good threads on here but after a couple days of browsing I haven't found them. Anyone have any links or tips?

Thanks,
Eric

[Naptown]

What kind of roofing can span 5' between purlins?
Depending on snow and wind loads you can spread out the racking to support along the short side only.
But would need to know those loads to determine racking type

[EricF]

It is a steel building, It uses a ribbed steel panel. I think the style used on my building is called PBR but the span is 5' between purlins.

[emartin00]

Give the guys at S-5! a call. They are very knowledgeable about metal roofs, and should be able to offer you a solution.

[Naptown]

It is a steel building, It uses a ribbed steel panel. I think the style used on my building is called PBR but the span is 5' between purlins.

What is the design snow load there?

[EricF]

I'm just under 1000' so they say no snow load 20 PSF Live Load. Once I get over 1k' then they go to 20PSF snow load.

[solarix]

If you are going to go with the 10deg pitch then just mount your rails crosswise to the purlins and put the panels on in "landscape" orientation to the roof. However, panels this flat will get dirty and not wash off very well in the rain. They will just get dirtier and dirtier. Here is a job we did on a similar roof.

[EricF]

I recall reading that 10 degrees was enough to clean effectively, sounds like you're experience says otherwise. Guess I have to look into that.

Running the panels up he roof instead of along the roof is a brilliant yet obvious alternative! I'll probably have to do that. Thanks!

[J.P.M.]

I recall reading that 10 degrees was enough to clean effectively, sounds like you're experience says otherwise. Guess I have to look into that.

Running the panels up he roof instead of along the roof is a brilliant yet obvious alternative! I'll probably have to do that. Thanks!

How effective a slope is at helping to keep panels clean is, to some degree, a function of how much (frequency) of rain events as well as the rainfall rate (how hard it rains), and how long a rain event lasts. More of the not exact nature of solar technology.