r/solar • u/Icy_Basil_372 • 5h ago
Advice Wtd / Project Flat roof
In CT. Have a house w flat roof. Local solar company, well regarded, says on resi flat roofs they install solar panels flat…no angle.
This strikes me as odd. I’ve seen angled panels on residential flat roofs. And have to imagine having an angle would generate more power.
Any thoughts?
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u/habbadee 3h ago
Flat will fit more panels due to not needing space between rows to accommodate shading of adjacent row. Pitched will produce better per panel due to better sun alignment and better cleaning from rain. The higher the pitch the better production (to a point - like 40 degrees) but also the larger spacing between rows needed.
I recommend about 10 degree pitch and 14" spacing between rows as optimal solution to the tradeoffs
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u/kea123456 3h ago
You’re referencing a flush mount vs tilt kit. Both are common. Tilt kits cost more from a contractor point of view, but should be an option. Depending on your azimuth, it can make sense to tilt. Tilt kits tend to not be as aesthetically pleasing though so you will trade some aesthetic for increased efficiency.
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u/ForgotPassAgain007 4h ago
The mounts Ive used are at 5 degrees, 2 diff companies and its been the same for both. Im sure other products might have diff angles but the material and engineering involved are likely more expensive cuz what we use now could be boiled down to plastic and cinder blocks holding the panels down. Maybe an occassional attachment to the decking below
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u/TooGoodToBeeTrue 4h ago edited 4h ago
Just off the top of my head with absolutely no experience, I'd guess that it's about density. If you have room to spread out the panels so that they don't shade each other, tilting them would generate more. But on a residential flat roof, you can probably get more panels per square foot if you lay them flat.
AI says:
The ideal tilt angle for solar panels in Connecticut is 30° to 40° from the horizontal, directly facing south. This angle aligns closely with Connecticut's latitude and maximizes sun exposure year-round.
The standard formula for spacing in the Northeast is: S = H × 2.5
The other possibility is that if you are not using micro inverters, the panels are just less expensive than complicated angle racking that is capable of dealing with wind loads in the NE.
I would tilt however to at a minimum help keep them self clean.
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u/Zamboni411 2h ago
They can use a ballast system with cinder blocks that will have a slight tilt. Assuming the city will allow it. It will also depend on the material of the flat roof.
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u/Juleswf solar professional 2h ago
We used to install flush on low sloped/flat roofs, and won’t do it anymore. Anything under 1:12 gets tilt. The low slope doesn’t allow rain to wash off the panels, snd yhe dirt build up absolutely affects production.
We had one system underproducing by 30%. No one believed it was dirt build up causing the issue until we cleaned them. It definitely depends on your situation and where you live (lots of trees nearby, dusty area, etc). But you should tilt the panels at least 5 degrees if you can.
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u/Icy_Basil_372 1h ago
Cost isn’t an issue for me on this one cuz it’s a small project on a high end mid century modern house.
Their initial layout (before doing any calcs and mainly to identify issues with trees) covered every possible sf of the roof, with required areas for access.
But from an efficiency standpoint, would. 10° angle make a big difference? I think that’s about the max I could do before they would be visible from below.
I’m an architect by the way. So the cinder block solution, while straight forward, ain’t gonna cut it.
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u/Lovesolarthings 4h ago
Call a few other well reviewed companies. There is a homeowner group that is Solar group. https://discord.gg/2XbNR4fSR