Residential · Southern Village, Chapel Hill
One clear plane in a canopy lot
A smaller array than the customer asked for, and more production than the alternative.
- Array5.7 kW DC
- Modules13 x 440 W
- Planes used1 of 3 available
- Best plane TSRF89 percent
Record
Full specification
- Array
- 5.7 kW DC
- Modules
- 13 x 440 W
- Planes used
- 1 of 3 available
- Best plane TSRF
- 89 percent
- Rejected plane TSRF
- 58 percent
- Modelled year one
- 7,050 kWh
The problem
The owner wanted 9 kW and there was roof area for it. Two of the three available planes sat at 58 and 64 percent total solar resource fraction because of a dense poplar stand on the adjoining lot that cannot be touched.
Adding modules on those planes would have raised system cost by roughly 55 percent for a production gain closer to 30 percent.
What we did
Filled the one clear plane at 89 percent TSRF and stopped there.
Published the per plane shade numbers in the proposal so the decision was the owner's, made with the arithmetic in front of them.
Left the design battery ready, since resilience rather than offset was the better next purchase for this household.
What happened
5.7 kW DC producing a modelled 7,050 kWh, about 64 percent of the home's 11,000 kWh consumption.
Cost per modelled kWh came out roughly 19 percent better than the 9 kW alternative.
The owner added a 13.5 kWh battery the following year rather than more modules, which was the right call for the site.
Turning down half the array we could have sold produced a better outcome for the customer and a shorter payback. Shade numbers belong in the proposal, not in the installer's file.
From the owner
They talked us out of a third of the system we walked in asking for, and showed us the maths for why. That is how we ended up recommending them to half the street.
Next
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OpenStart with the numbers, not a sales visit
Send twelve months of kWh and a roof photo. You get a sized system, a production model and a payback figure before anyone comes out.
No pressure appointment. The site check is free and the design is yours to keep.