Solar panels on a flat roof - tilt or no tilt?

[dusterbuster]

Hey guys, the installer came back with a proposed plan that incorporates a 10-degree SW tilt. The designer said he didn't want to go too high because we have a short parapet around the roof of our 1 story home (so hopefully the panels remain unseen from ground level) and to reduce spacing between the panels. Do you think a 10-degree tilt will be sufficient to help keep the panels clean?

Also, to provide the tilt, the installer has switched the mounts to Ironridge Tilt Leg and Foot w/Chemlink E-Curb (rather than Quick Mount PV QMNC Q Base Comp for a flush mount). In comparing the diagram of the tilt versus flush mount, it looks like there is a bit more waterproofing required with the tilt leg mount (although maybe that is just manufacturer specific to Ironridge). Should I have any concerns that a tilt leg mount may increase the likelihood of water intrusion?

[DanKegel]

SW tilt!

(Also consider bifacial panels; with tilt mounts, they could get a fair bit of light on the back side.
Probably not competitive, but ask just in case.)

[J.P.M.]

As others have pointed out horizontal orientation has drawbacks, the most practical being a much more frequent cleaning schedule if reasonable performance is to be maintained. A SW orientation of around 30 deg. or maybe a few degrees more would be a reasonable estimate for a decent orientation. Avoid horizontal orientation.

[dusterbuster]

Thanks everyone for the helpful comments. I've told the installer that I would like the panels mounted at the appropriate tilt, so they are going to see what they can come up with.

[SunEagle]

While I agree a SW tilt is best depending on the amount of roof space, tilting the panels will create shade issues if there isn't enough spacing between rows. That might limit the total installed wattage.

[solarix]

Whatever you do, don't have them installed flat - unless you want to be up there cleaning them all the time. Tilted panels will keep themselves pretty clean just with rain washing them, but on a flat orientation the dirt will just build up and up. Installers like to orient the arrays to the roof framing of course, but there is no reason (with significant extra hassle) they can't go diagonally across the framing. Generally though, if you are within 30 degrees of south, go with it.

[Mike90250]

Agree with SW for increased peak hours harvest

[emartin00]

I would strongly suggest a SW tilt. Southwest orientation will give you more power in the afternoon, when you would be using it. There is actually a significant push to start installing West facing arrays, because they produce power when people come home and turn on the AC.
As you said, the tilt will also help water shedding, and keep them much cleaner.

[dusterbuster]

I just received the proposed site plan from our solar installer (11kw system in Santa Monica), and noted that they propose flush mounted panels on our flat roof (no tilt). Our house is oriented about 45 degrees off axis, such that if the panels were mounted and lined up along the roof joists and tilted, they would either have to be tilted southeast or southwest. We get a ton of sun exposure (no shade issues) here in Santa Monica. It would seem that tilting the panels SE or SW would mean increased efficiency for half the day, and decreased efficiency for the other half. I'm wondering if this might be a reason the installer proposed a flush mount, or whether they were just trying to minimize installation costs/time.

Also, even if it's true that a flush mount would be the appropriate layout for our situation, I'm wondering if the panels should at least have a slight incline (5 degrees maybe?) to help reduce dust accumulation on the panels when it rains (which admittedly is very rare in these parts lately).

Any thoughts/recommendations would be great appreciated. Thanks!

UPDATE:

Hey guys, the installer came back with a proposed plan that incorporates a 10-degree SW tilt. The designer said he didn't want to go too high because we have a short parapet around the roof of our 1 story home (so hopefully the panels remain unseen from ground level) and to reduce spacing between the panels. Do you think a 10-degree tilt will be sufficient to help keep the panels clean?

Also, to provide the tilt, the installer has switched the mounts to Ironridge Tilt Leg and Foot w/Chemlink E-Curb (rather than Quick Mount PV QMNC Q Base Comp for a flush mount). In comparing the diagram of the tilt versus flush mount, it looks like there is a bit more waterproofing required with the tilt leg mount (although maybe that is just manufacturer specific to Ironridge). Should I have any concerns that a tilt leg mount may increase the likelihood of water intrusion?