Any one using the standing seam metal roof mounts?

System

They look AWSOME and would fit my application perfectly!

Do I need 6 per panel or can 3 on adjoining side link two panels?

crewzer

Re: Any one using the standing seam metal roof mounts?

Mounts like these from Unirac?




I’d urge caution in considering this type of installation. Five areas of concern are:

1) PV module power output drops as the module temperature increases. Mounting modules close to a roof may reduce the flow of cooling air behind the modules, which would in turn lead to reduced power output (reduced array voltage).
2) Ambient temperature near a (dark) metal roof could further increase module (cell) temperature, causing yet additional power reduction (reduced array voltage).
3) A significant array voltage reduction due to high module (cell) temperature could result in a summer array voltage too low to reach target battery charging voltage targets.
4) Azimuth and/or tilt angles may not be optimal for best seasonal- or year-round power production (less array current).
5) A low tilt angle may lead to dirtier modules, which would require more maintenance and/or lead to yet further power reduction (reduced array current).

References: http://www.sunfrost.com/extreme_efficiency.html (see: “PV Power”)
And http://america.sma.de/glossary.html#mounting (see: “Mounting Style”)

In short, look for ways to install the array well ventilated (cool), clean, well-aimed, and optimally tilted.

HTH,
Jim / crewzer

icarus

Re: Any one using the standing seam metal roof mounts?

Jim,

How much air should there be under a panel that is roof mounted?

I had my panels sitting directly on the asphalt roofing for several years (because I didn't know any better!) I now have the roof mounted panels about 3" above the roof. It would seem if you are going to do a roof mount on standing seam, these mounts would be great. You give up some efficiency with a roof mount, but you (may) make it up in convienence. My question is, is the 1" standing seam rise enough air under the panel, given the need to mount on the roof?

Icarus

Ralph Day

Re: Any one using the standing seam metal roof mounts?

Personally i'd use the standing seam mounts to hold a rack base and tilt the panels to the optimum angle.

Also read here or somewhere about ice getting under the panels as it sheds the roof...then re-freezing and damaging the underside of the panels...ice very strong! Maybe it was ice sliding. Maybe put the panels at the apex of the roof, then nothing sliding down to meet the array? A little more cable to aleviate a serious problem for the winter. Probably not a Solar Guppy worry in his aquarium area.

Ralph

icarus

Re: Any one using the standing seam metal roof mounts?

Ralph makes a good point about ice under the panel.. In my clime it would be a problem on the lower portion of my roof. Putting the panel near the peak would solve it. Never underestimate the power of ice.

I am at present waiting for our ice to break up. It looks like it may yet be another three weeks. The ice is loose from the shore, an with the wind has amazing power, power in slow motion!

Icarus

System2

Re: Any one using the standing seam metal roof mounts?

The roof is 33 degrees and the roof is silver so the adjacent dormers will actually reflect onto the panels more.

and yep those are the ones...

What ever I use will be a fixed angle.

mike95490

Re: Any one using the standing seam metal roof mounts?

Consider leaving a gap between panels or rows of panels, for air flow.

crewzer

Re: Any one using the standing seam metal roof mounts?

How much air should there be under a panel that is roof mounted?

Tony,

SMA says that anything less than 6” is considered “mounted flat against the roof”. See: http://america.sma.de/glossary.html#mounting

The “Module Mounts and PV Performance” article in the April/May 2008 issue of Home Power magazine (#124, page 61) addresses this very issue on a couple of installations in Oregon. In brief, a rack-mounted array tilted at 30 degrees and installed on a flat roof experienced a +22 C temp rise above ambient when exposed to high insolation (900 W/m^2 to 1,000 W/m^2).

However, a “parallel to roof mount” array located 4.25” above the roof surface experienced a +34 C temp rise above ambient when exposed to high insolation (900 W/m^2 to 1,000 W/m^2). The 12 C temperature differential translates into power loss of ~5% to 6% for the “parallel to roof mount” array.

Accordingly, it seems to me that the answer to your question is two-fold: Go for pole-mount or rack mount if possible. If parallel-to-roof-mount is a must, then the air gap should be six inches or more. That probably means that ~4" spacers (minimum; and much longer screws) would be required for the Unirac system mentioned above.

HTH,
Jim / crewzer

icarus

Re: Any one using the standing seam metal roof mounts?

Jim,

Once again thanks for your learned response.

My roof was built with the ideal year 'round angle for panels. I will use standing seam mounts in a heart beat, even at the expense of 5% reduction in capacity. The trade off in the simplicity of the mounting and operation. It would be interesting to do a test to see, with 3" of airspace under the panel, what kind of thermal draft would be created with the heat rising up the roof creating a draft under the panel.

We have about 2 months where the temps would be much of a problem, the other ten months are cool or cold enough to mitigate the losses of the heated panels. Of course, the hot months happen to be when we have 12-14 hours of sun on the panels, and we don't need lights until after 10PM so the loads are almost nil.

Once again, thanks for the advice..

Tony