Lapping PV panels to create water shedding roof. Thoughts? Comments?

[galstaf]

Hey all,​

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So I am kicking around some concepts to use PV panels as actual roofing on a carport/lean to cover. I am looking at using low cost used panels and then "lapping" them (without covering the cells obviously) so that the upper panel sheds water onto the panel below and the water doesn't drip thru into the space below. ​

From what I have seen you can get used panels now for not much more that it would cost to buy a similar sized sheet of plywood! (I am only partially kidding). ​

The panels will be held up by 2.5"x2.5" galvanized steel square tube often used on carports and barns. I have a steel sided barn rated to 130mph winds that uses these as roof and wall structure 60 inches on center spacing. ​

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I have the tubing spaced 42 inches apart in my concept carport, so I feel that should be plenty strong. ​

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I will add some concept pics to help you visualize (obviously not completely showing all bracing etc). ​

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Questions: ​

• Has anyone done this or something similar? If so, any comments on how it worked out or what you would do to improve?​

• Any recommendation on the slope of the roof for an installation in Georgia/South Carolina?​

• Any recommendation on wiring these up... look at one big inverter, micro inverters etc?​

• Any recommendations on how to attach to the galvanized steel tubing?​

• How much spacing should there be between the long edges for expansion/contraction?​

• Any recommendations on flashing in between the long edges of the panels to help keep water from shedding thru.​

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[galstaf]

 

[DThames]

Maybe just butt them up and seal the joints. Example.

 

[740GLE]

Flat roof? I take it you don’t plan for snow loading even for those freak snow storms you get?

 

[galstaf]

Flat roof? I take it you don’t plan for snow loading even for those freak snow storms you get?

Not flat. Probably about 10ish percent incline I would think.
We don't get a lot of snow, but the braced steel at 40 inches should be plenty to support it.
Hence the questions I asked looking for feed back from people that have tried it or experienced it.

 

[galstaf]

Maybe just butt them up and seal the joints. Example.

That seems more inclined to leak, no? It would seem that the sealant would tear apart with movement of the panels with heat.

Hence why roof shingles and most roofing materials are lapped over each other so even if the sealant failed, the water would be less inclined to work itself in.

 

[galstaf]

Maybe just butt them up and seal the joints. Example.

Thanks for the link tho.. I have googled for it, but found very little. Not seen this guy before.

 

[galstaf]

Not flat. Probably about 10ish percent incline I would think.
We don't get a lot of snow, but the braced steel at 40 inches should be plenty to support it.
Hence the questions I asked looking for feed back from people that have tried it or experienced it.

Actually it appears that it should be somewhat steeper.

Your optimal year-round tilt angle:
28.6° from horizontal
Your optimal tilt angles by season:

• Spring: 28.6°
• Summer: 13.6°
• Fall: 28.6°
• Winter: 43.6°

Your optimal tilt angles by month:

• January: 38.6°
• February: 33.6°
• March: 28.6°
• April: 23.6°
• May: 18.6°
• June: 13.6°
• July: 18.6°
• August: 23.6°
• September: 28.6°
• October: 33.6°
• November: 38.6°
• December: 43.6°

 

[timselectric]

Just put metal roofing panels under the solar panels.
And never worry about it again.

 

[Rednecktek]

It wouldn't hurt to overlap the panels a bit side to side so the end of one panel lands on the center gap of the next 2 panels. You might get good runoff from the panels being lapped but with your current design you're going to have a lot of water coming in those long straight runs between the panels.

Or just get a metal roof and call it a day. Either way you're going to need more slope.

 

[time2roll]

I would be laying them flat with each other and glue/seal them together with adhesive caulk of some sort.
Even if you lap them, water will go between on the side edges. Mounting flat seems way easier and since you must seal the side edges may as well seal the whole thing. Seal will hold better if held down firm and stable.

I don't know the best sealant to use

 

[galstaf]

Just put metal roofing panels under the solar panels.
And never worry about it again.

I was looking at the possibility of using bifacials. They would allow a little light thru for better visibility under the structure and be a lot more attractive that a straight metal roof.

 

[galstaf]

It wouldn't hurt to overlap the panels a bit side to side so the end of one panel lands on the center gap of the next 2 panels. You might get good runoff from the panels being lapped but with your current design you're going to have a lot of water coming in those long straight runs between the panels.

Or just get a metal roof and call it a day. Either way you're going to need more slope.

Yes on slope .. the design is just to show the concept. Ideal angle is about 28 degrees for our latitude.

The centers along the beams could be closed up and caulked... but I was also wondering if someone could suggest a low cost flashing idea to push the water back onto the panel. The flashing could be lapped also, or if flexible enough, could also run down the top of the long side of the panels in one long run.

 

[galstaf]

I would be laying them flat with each other and glue/seal them together with adhesive caulk of some sort.
Even if you lap them, water will go between on the side edges. Mounting flat seems way easier and since you must seal the side edges may as well seal the whole thing. Seal will hold better if held down firm and stable.

I don't know the best sealant to use

Hence the ask on a flashing idea, or just butt connecting on the long edge with sealant on the long edge.

You think there will be no leak thru if they are butted up to each other? I have never installed a full array before, so I have no experience with this.

 

[timselectric]

I was looking at the possibility of using bifacials. They would allow a little light thru for better visibility under the structure and be a lot more attractive that a straight metal roof.

Next best option is to build a grid type gutter system under all seems. Probably could be done with 1" pvc.

 

[galstaf]

OK.. well I did ask for a suggested angle.. apparently 23 to 28 percent is best for my latitude. As my main concern is to generate AC cooling power during the hottest months and to provide a shading for the vehicles underneath, I have picked 23 percent. This would create 10 feet of elevation change over the 27 feet in the diagram.

 

[galstaf]

Flashing wise, something like this is what I had in mind.. kind of a T-shape rigid flashing that could be screwed thru to hold the PV panels in place and be sealed along the underside edge.

I just don't know what to search for to find a product like this. Can anyone suggest something that could work that would push the water back onto the panel and stop it leaking thru.

 

[galstaf]

Or could the flashing be skipped.. push the panels closer together and would a silicon sealant suffice?
How much would the panels shift around due to weather and temperature?

 

[galstaf]

Next best option is to build a grid type gutter system under all seems. Probably could be done with 1" pvc.

Hey @timselectric ...
How would that work? Not sure I understand what you are getting at. Could you suggest a picture or link?

 

[peakbagger]

There was a company on the internet that made that sort of seal for solar panels. They were used on a couple of high end architectural wonders. I expect the company went out of business after the inevitable lawsuits. Its tough application especially at corners.

I would think a bellow type seal with a thin piece of flashing bent in sharp upside down "V" The two pieces of the V would be attached to the adjoining side rails of the panels and then a poly sealant bead would be run down the seam between the metal and the frame.