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

[timselectric]

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

Think of PVC pipe, cut in half long ways. To form a gutter. Using T's and 4 way fittings to form a grid under all seems. If panels are placed tightly against each other with weather stripping between them. All that you have to catch are the drips that find their way through. So, it wouldn't have to be very large of a pipe/gutter. The hardest part would be fitting it between the panels and support structure.

Actually, it's not going to work well. But, I'll leave it up, to possible inspire other ideas.
Maybe aluminum C channel would be better. So that it can be part of the support system. The seems could be brazed together.

 

[Zwy]

I've butted long panels together, they aren't always perfectly straight to the next panel.

You say you get snow and any roof system needs to have snow load calculation done if there is any snow load ever on the structure. The information for your location is out there. Another is wind speed, you need a structure that can wind speed and believe me, it's more windy 15 feet off the ground than standing on the ground.

Go here, input your address, use Risk Cat 1, your soil type and it should give you max wind speed rating and snow load. https://skyciv.com/wind-load-calculator/

I've used similar before, the USGS spits out the data.

 

[SolarForU2]

Cover your roof with clear commercial green/tunnel house film, them mount the panels above that using the normal alloy rails etc.
That's what we did over the roof of a small shed containing a diesel generator. We used a semi-clear film that had an embedded nylon mesh, its extremely strong and should last 20 years.

Any attempt to butt joint those panels together without leaks is an exercise in futility.

Mike

 

[740GLE]

Trex has a rubber membrane for deck installations for multi story decks to prevent water from falling underneath, it droops between joists and channels water away.

 

[z_zk_z]

To Galstaf: I am presently building a carport out of wood & struts with solar panels on its roof. I want to make a comment on the tilt angle. Mine (in Jacksonville, FL) should have a tilt angle about 26-30 degrees, however after studying the solar carports on internet (mostly having flat roofs), I decided to go with only 10 degrees because it was going to be very difficult (very tall on one side) to build such a carport (with 30 degree tilt angle over 20 feet spacing between short and tall walls). I also dropped the wall height (on the short side) to only six feet. I came to the conclusion that lowering the tilt angle should be okay in my case because I am using many extra panels and at the same time, it will make it much simpler to build the carport.

 

[JLBinTN]

You'll likely have plenty of drips, but i see no structural reason why you can't do what you're suggesting.

 

[JCSchwarb]

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

That’s what we did. Used self tapping on all sides, to pull silicone in to seal them. If you need 100% water proof, use a double bubble underlayment first. Used 6x6 poles on all side, 13’ on the high side and 9’ on low side, 20’ length. Used a pole barn kit with metal trusses and 2x6x12’ PT. See pics.

 

[PreppenWolf]

I would just place corrugated steel under it and mount the panels on top. Leak problem solved and minimal weight added.

 

[aaroncgi]

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.


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Something like the trim used to seal between polycarbonate sheets on greenhouses may work. It looks highly similar to what you suggest:

10mm Aluminum Base & Cap - Anodized Finish - 30 Base Screws & 30 Cap Screws Included w/24’ Piece - Duralight Plastics

The aluminum base and cap install system is used to connect multiwall sheets together, providing a finished, professional look.

www.duralightplastics.com

 

[galstaf]

That’s what we did. Used self tapping on all sides, to pull silicone in to seal them. If you need 100% water proof, use a double bubble underlayment first. Used 6x6 poles on all side, 13’ on the high side and 9’ on low side, 20’ length. Used a pole barn kit with metal trusses and 2x6x12’ PT. See pics.

Thanks JC! So the butt joints have not separated at all? How much leak through do you get? Occasional drip or full on puddles underneath?
Double bubble seems like it would be a good choice option.. still translucent so the bifacial panels have the chance to make a little extra.
Could you possibly make suggestions on the pole barn kit and double bubble, please? Were you happy with what you went with?
Any other gotchas or tips?
Thanks again and hope you are having a good holiday!

 

[galstaf]

I would just place corrugated steel under it and mount the panels on top. Leak problem solved and minimal weight added.

I gotcha, but that kills the potential of bifacials. Also right now, even 29 gauge corrugated is 4 to 5 dollars a linear foot, so it also adds a not insignificant amount of cost.
My whole point is to make a roof with about the same cost as corrugated that also creates power.

 

[galstaf]

Something like the trim used to seal between polycarbonate sheets on greenhouses may work. It looks highly similar to what you suggest:

10mm Aluminum Base & Cap - Anodized Finish - 30 Base Screws & 30 Cap Screws Included w/24’ Piece - Duralight Plastics

The aluminum base and cap install system is used to connect multiwall sheets together, providing a finished, professional look.

www.duralightplastics.com

Mmm good suggestion. Have you used these, Aaron?

 

[12VoltInstalls]

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

guy sounds like he’s on helium

 

[12VoltInstalls]

push the panels closer together and would a silicon sealant suffice

Silicone isn’t great for roofing applications or below the waterline.
Silicon would add too much VOC to the panels and be hard to solder in.

Polyurethane would be my choice

 

[RussNM]

If youre hell bent on trying this Id use this or something of similar composition. this is far superior to silicone. https://www.homedepot.com/p/Loctite...e-Roof-and-Flashing-Sealant-1675273/203163733
Ive used this for years and going back to jobs where this was applied (on the roof in high altitude desert solar radiation) it was still flexible and didnt let loose like silicone.

 

[12VoltInstalls]

decided to go with

Ive used this for years and going back to jobs where this was applied (on the roof in high altitude desert solar radiation) it was still flexible and didnt let loose like silicone.

Exactly.
It’s not intended for below the waterline but I’ve used the white on fiberglass and aluminum boats for almost 20 years now including a few of my own for through-hull sealant. Can’t get a better litmus than that lol

 

[HighDesertOffgrid]

Silicone isn’t great for roofing applications or below the waterline.
Silicon would add too much VOC to the panels and be hard to solder in.

Polyurethane would be my choice

Silicone is for cleavage. Urethane (or Butyl) is for sealing.

 

[JCSchwarb]

Silicone is for cleavage. Urethane (or Butyl) is for sealing.

Thanks JC! So the butt joints have not separated at all? How much leak through do you get? Occasional drip or full on puddles underneath?
Double bubble seems like it would be a good choice option.. still translucent so the bifacial panels have the chance to make a little extra.
Could you possibly make suggestions on the pole barn kit and double bubble, please? Were you happy with what you went with?
Any other gotchas or tips?
Thanks again and hope you are having a good holiday!

Specifically, Lexel is the sealant I used with very good success - I have a drip here or there that will be sealed before our next rainy season; https://www.sashco.com/products/lexel/. I agree with others that silicone is not the best and black butyl while cheap is not compatible with this type of project and will look like hell. Regarding double bubble wrap, I used this product, link below, also check your local metal roofing supply to check their shipping prices. They sell 3-4” aluminum tape so you can make any width. Also using a aluminum tape on all seams over the sealant may work too, but would not be worth it IMHO. https://insulationstop.com/product-category/single-bubble-foil. If you are in north FL I can point you to an excellent company, otherwise suggest looking for pole barn supply company close to you. They will provide everything including posts, metal trusses and 2x6” PT. If you wanted more energy under the panels, you could add 2x4” stand-off at every edge where panels sit. Would be fast and easier to install panels and protect underwrap.

 

[12VoltInstalls]

Specifically, Lexel

That is a great product for many things. It’s not very good at a lot of caulking tasks imho. But it’s fantastic on roofs, aluminum, squirting inside MC4s, even emergency patches on boats, waterproofing plastic conduit issues, etc. I always have one of the high priced squeeze tubes on hand, and usually a caulking gun tube as well.

It lasts forever on roofs it seems. Which is odd to say because I can tell you for sure it doesn’t seem to always stay stuck very long under the waterline on boats. But it’s still great for quickie temporary or emergency fixes on boats because it doesn’t care if the surface is slightly damp to stick (it does seem to care deeply that the surface is clean).

 

[HighDesertOffgrid]

This is me about to "repair" another Lexel repair. Similar to Silicone (and Growatt), failure was nearly guaranteed within 24 months. Your results may vary.