Minimal separation from flat roof with silicone coat

[bmh]

Hi All,

I am planning to install rigid solar panels on flat roof already coated in silicone. The roof has plywood, then thick layer of tar (it used to be tar and gravel originally) with several various coatings: asphalt emulsion coating, another acrylic coating that prevents yellowing of silicone, and silicone on the top.

The roof has slight angle, and there are little bumps all over.

Silicone coating does not get warm at all to touch. Maybe little bit when temperature reaches low 100's which is max for my hometown.

Now, I want to install rigid solar panels on the top. I read there should be least 3 inches of separation between panels and roof surface for heat disipation. Is this true, and do I have to consider this given my roof surface never gets hot thanks to silicone?

I have to position panels at 45 degree to the roof orientation to make them face south. I would like not use rails that touch roof surface because it will disrupt rain water flow, and maybe cause ponding.

In my area, we can have lots of wind upto 80, 90 mph, so I would like panels to be as low as possible. My roof has parapet walls that should provide some protection from wind. However, I read there should be some small angle to prevent water ponding and dust getting stuck on the panels' surface.

What would be a simple mounting system that provides small tilt to solar panels on silicone roof? When mounting, do I have to find roof beams and screw into them, or I can just put screws into roof plywood, and add vhb tape for silicone, and perhaps glue for silicone, and some sealant?

Did I miss anything regarding installation on flat roof?

If anyone has related experience, I would appreciate your thoughts/ideas.

Thank you.

 

[MisterSandals]

I was looking forward to a good “frat roof” story.

Anyway, LOTS of this has been hashed out already with a lot of ideas and solutions. Have you tried the search?

Search results for query: Mounts

diysolarforum.com

 

[bmh]

I was looking forward to a good “frat roof” story.

Anyway, LOTS of this has been hashed out already with a lot of ideas and solutions. Have you tried the search?

Search results for query: Mounts

diysolarforum.com

Will do. I fixed the title. Thanks for pointing out.

 

[svetz]

I read there should be least 3 inches of separation between panels and roof surface for heat disipation. Is this true...

The air gap is for panel cooling as panels are less efficient when hotter. So, the real question is how much efficiency do you lose?
You can find that out by using the temperature correction factor from the panel datasheet and conducting some experiments on your roof with a black painted metal object and and IR gun (two temps, one elevated with good air flow and flat). Let us know where you live and what you find, probably a big difference based on average air speed and humidity. If you need help with the calculations post a link to your panel's datasheet with the temperature correction factor, your two temperatures and someone will show you the math for the efficiency loss (it might not be much).

...I have to position panels at 45 degree to the roof orientation to make them face south...

Unless you're maximizing power for winter, that sounds too steep for a flat roof with no tilt. I've heard 10° is all you need for self-cleaning. Mine are about 7° over a silicone roof and except for winter/spring we get plenty of rain and it's not an issue (dirt collects on the bottom inch). The exception is pollen season when they literally turn yellow and I have to hose them off.

I would like not use rails that touch roof surface because it will disrupt rain water flow, and maybe cause ponding.

I use stand-offs, see: https://diysolarforum.com/threads/an-enphase-ensemble-installation.3603/post-35283

 

[bmh]

The air gap is for panel cooling as panels are less efficient when hotter. So, the real question is how much efficiency do you lose?
You can find that out by using the temperature correction factor from the panel datasheet and conducting some experiments on your roof with a black painted metal object and and IR gun (two temps, one elevated with good air flow and flat). Let us know where you live and what you find, probably a big difference based on average air speed and humidity. If you need help with the calculations post a link to your panel's datasheet with the temperature correction factor, your two temperatures and someone will show you the math for the efficiency loss (it might not be much).


Unless you're maximizing power for winter, that sounds too steep for a flat roof with no tilt. I've heard 10° is all you need for self-cleaning. Mine are about 7° over a silicone roof and except for winter/spring we get plenty of rain and it's not an issue (dirt collects on the bottom inch). The exception is pollen season when they literally turn yellow and I have to hose them off.


I use stand-offs, see: https://diysolarforum.com/threads/an-enphase-ensemble-installation.3603/post-35283

Thanks for your information.

I was wondering if there was a ballpark number for separation between panels and roof surface. I am in Albuquerque with sunny flat roof and 2050 hours of sunshine anualy.

I haven't selected panels, yet. I am trying to find a good guide for installing solar home system on flat roof. So far, I wasn't that successful. If you know any, please let me know.

I saw your flat roof setup. Looks rock solid, but my concern is very strong wind I can get at my home. Therefore, I am inclined to install panels as low as possible, and that would be cheapest option, too. Your system seems too high from the surface given strong winds I can get.

45 degree angle is not tilt. My garage roof where I plan to put panels on, faces southwest. So, I have to position panels 45 degree to that direction. I am planning to have tilt zero due to strong winds.

 

[svetz]

In you go to a solar racking site and use a calculator (e.g., iron ridge) you can see the forces applied at various angles and height. Or rather they tell you the number of attachment points and you can lookup the pullout strength of the screws.

... saw your flat roof setup. Looks rock solid, but my concern is very strong wind I can get at my home....

They are rock solid, code mandates they survive 170 mph hurricane force winds. Mine are actually considered "flat", that is the slope is the same as the roof slope, that's because even small angles really increase the forces. I calculated it once, at the "optimum" angle (~22°) it was something like having a herd of elephants on the roof (e.g., many tons of force), strong as the roof is... decided "flat" was best (you can always add a few more panels to make up the losses).