The Monkey House

< Writing : Other : PV Solar >

Solar Expansion 2: Electric Hullabaloo

North-facing solar in Wisconsin? YES! I'm doing one last expansion to max out my inverter's electrical capacity, but I'm out of roof space. Out of 'south' facing roof space, anyway. So I'm installing a third of the new capacity at 300 degrees azimuth, 30 degrees north of due west. My roof is fairly flat, only 18 degrees tilt, which makes this practical. Simulation says the 'west' facing panels will be just over 80% as productive as the 'south' facing ones. Probably slightly less than that in practice as there's a tree in the neighbor's yard that shades those panels a bit as well.

Costs are higher now than when I did my first expansion: inflation, higher labor costs, plus more total labor since this isn't just a matter of installing new panels but of moving around some existing panels to make room, and THEN installing the new panels. I'm adding four more panels of 400W each to the SSW roof plane, and two more 400W panels to the WNW roof plane. This expansion barely moves the needle on overall system cost-per-watt, bringing the total system down by only a nickel a watt. Even correcting for the reduced yield from the northwest-facing panels, the new capacity is about the same price on a delivered-energy basis as the previous system as a whole.


Some basic modeling indicates that I should get about 27% more energy from about 30% more nominal panel capacity. As before, this estimate excludes the effects of aging and shading, so the energy I get over the next five years will not be 27% higher than what I got over the past five years. Probably I will yield only about 15% more energy over a five-year period, even if that is 27% more than I would have yielded without the expansion.


Here's an updated version of the costs table from Part Four:

$5,550Base price for 2400Wdc upgrade$2.31/W
($1,665)Federal tax incentive (ITC)$0.69/W
$3,885Actual upgrade cost$1.62/W
$14,983Pre-expansion system cost$1.85/W
$18,868Post-expansion system cost$1.80/W


My original system, operated over two years, yielded $1400/yr in value. Based on that, I expected my first expansion to increase yields by about $500/yr. But in reality, the average yield over the subsequent five years was just over $1600. Aging, shading, and changing rate structures took their toll. If I do that same optimistic prediction again, I expect these panels to be worth about $450/yr and my total system will reach simple payback at the end of 2027. But if I lose another 5% when my panels are another five years older and another 5% on top of that because those darn trees keep growing, then it will be some time in the middle of 2028 that the system is fully paid for.

100MWh should happen in 2028 too, so expect that to be the next update. See you then!

Version 1.0     |     Originally written: October 13, 2023     |     Latest revision: May 22, 2024     |     Page last generated: 2024-06-08 08:09 CDT