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Standoffs racking can add over 4% vs flush-mount racking

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holeydonut

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Jun 27, 2020
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Thanks to @Redhill_qik for posting the link about the CSI-EBPP estimator:

I guess this tool is a similar thing to PVWatts, and is used by California utilities to do some weird maths around their solar/incentive programs. You can punch in your array spects and it'll estimate the annual production based on major factors of the array.

One interesting independent variable is the racking type which establishes the height/distance the racking will be away from the roof (presumably it's the distance from the tile/shingle layer; not the underlayment or actual decking).

Using my combination of panels, inverters, inverter efficiency, zip code, shading, azimuth, and tilt... but varying the "Mounting Method" ... I get these annual kWh estimates:

> 6" Average Standoff: 11,121 kWh
> 3" up to 6" Average Standoff: 11,074 kWh
> 1" up to 3" Average Standoff: 11,006 kWh
> 0" up to 1" Average Standoff: 10,809 kWh
0" Flushmount or BIPV: 10,658 kWh

So the difference between Flushmount and > 6" is 4.344%. Of course normal tile-hooks with some aesthetically pleasing skirts will land somewhere in the middle. I guess the extra height away from the roof plus airflow helps with cooling of the panels and maybe the convection/cooling of the inverters (Enphase inverters cool via convection).

So my inference is that fugly-ass 7" standoffs give a bit more juice than those sexy-as-hell Tesla solar roofs. This isn't a huge deal if you have a HUGE AZZZ roof and can just overfill with panels. But if you're space constrained like me and trying to get the most out of your PV system, then ugly stand-offs may be worth a consideration when compared to short mounts or tile hooks + skirts. For me the benefit is like... around 800 miles of EV range per year... Fancy stuff.
 
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