Panel height off the roof?

[HX_Guy]

Is there an ideal height that the panels should be off a tile roof, especially for out here in Phoenix? I see most of my neighbors that have solar seem to have the panels fairly close off the surface, maybe 5" to the panel frame. I set mine to 7" because I need to clear a plumbing vent thanks to my genius installer, should that be ok...any downsides to having the panels a bit higher?

[sensij]

Is there an ideal height that the panels should be off a tile roof, especially for out here in Phoenix? I see most of my neighbors that have solar seem to have the panels fairly close off the surface, maybe 5" to the panel frame. I set mine to 7" because I need to clear a plumbing vent thanks to my genius installer, should that be ok...any downsides to having the panels a bit higher?

Higher off the roof will tend to have better airflow and keep the panels cooler. Cooler panels will generate more, typically something like 0.4% per deg C. As long as you don't mind the look, and the wind loads are accounted for in the rack design, higher is fine.

[J.P.M.]

Is there an ideal height that the panels should be off a tile roof, especially for out here in Phoenix? I see most of my neighbors that have solar seem to have the panels fairly close off the surface, maybe 5" to the panel frame. I set mine to 7" because I need to clear a plumbing vent thanks to my genius installer, should that be ok...any downsides to having the panels a bit higher?

For the most part, mostly aesthetics in some eyes for the downside. As long as the wind calcs are OK, that's usually about it. Very large standoff dimensions may need some additional wind/seismic considerations but my guess is that an array would need a pretty unusual standoff dimension for that to become a concern. The biggest upside factor (and this is probably more qualitative than it is quantifiable in terms of an actual efficiency increase as a function of dimension) may be that in general, the more standoff, the more likelihood of better air circulation behind the arrays -->> more heat transfer from the arrays -->> lower array temp. -->> slightly higher efficiency and probably longer service life with fewer problems. Also, a bit easier to get at if service is required. In my experience, after about 2-3 weeks few people will notice the array, much less the standoff dimension. FWIW, mine's about 10.5" min. from bottom of panel frame to lower edge of tile on a concrete tile roof.

[Alisobob]

Too high.... and critters may nest under them.

[russ]

Too high.... and critters may nest under them.

2" is more than adequate for that - if needed openings can be screened.

[J.P.M.]

Too high.... and critters may nest under them.

Too high for what ? Aesthetics ? For starters, beauty is in the eye. Also, I doubt most arrays will ever win a beauty contest pretty much regardless of standoff. Also, I don't doubt that most folks stop looking at them all together after a short time anyway. As for critters, that's why God made screens.

[inetdog]

Rule of thumb for panel cooling by air flow underneath: Less than 4" can cause significant power loss and can also affect the load capacity of your wiring under the panels.
More than 6" is getting into diminishing returns for the effort and expense of raising the rails.
Your forced 7" should be just fine.

[foo1bar]

I set mine to 7" because I need to clear a plumbing vent thanks to my genius installer, should that be ok...any downsides to having the panels a bit higher?

I thought it was generally a bad idea to cover a plumbing vent with a solar panel.

[HX_Guy]

I thought it was generally a bad idea to cover a plumbing vent with a solar panel.

Thank my genius installer.

What's the thought behind it being bad though? If the vent still has clear space above it, would it cause it any issues?

[J.P.M.]

Thank my genius installer.

What's the thought behind it being bad though? If the vent still has clear space above it, would it cause it any issues?

Usually the vents need clear space above and adjacent to do their job - that is, venting in the best fashion possible. That job is helped along by unobstructed area above the vent to encourage something of a venturi effect - same way smokestacks work. Also, it may not be a good idea to have air that is probably close to saturation with H2O vapor and some other mixed gasses exiting so close to a panel, particularly at night when the array may be well below the dew point and act as a condensing surface with crud buildup as one possibility.

I believe the San Diego co. code does not allow such things. At least my building inspector doesn't. Vents must clear adjacent fixtures, arrays, walls, etc. by min. 6", with a few details about relative heights, etc. I moved two vents after checking with him before the array went up. It may be different where you are.

[HX_Guy]

Bah you guys and your making sense.

I'll see if there is a relatively easy way to move that one panel elsewhere so that the vent isn't covered.

[inetdog]

Bah you guys and your making sense.

I'll see if there is a relatively easy way to move that one panel elsewhere so that the vent isn't covered.

And just to complete the rainstorm on your parade, depending on what kind of vent it is the difference in air pressure with wind blowing under the panels may actually interfere with proper operation of the vent. Or lead to condensation of nasty stuff under the panels.
What kind of vent it is?

[HX_Guy]

I believe it's called a DWV vent? It's from one of the bathrooms, you can see it in this picture on the far right (with the loose wires around it)

[Mb190e]

We moved my sewage vent to the other side of the roof. from the attic it takes a couple 45's, 6' of pipe and a new hole. My installer was able to even reuse the flashing was real careful about how he took it out without destroying it.

[russ]

Good job and much better!