The Monkey House

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Solar Expansion

After analyzing data from the first year of operation, and taking into account better information about — and changes in — my electric load, I determined that I could use the production from additional solar panels covering my remaining south-facing roof area. Eight panels will fit on the roof, and conveniently this reaches the maximum string power for my second story string.


These new panels will be at a slightly less optimal angle than my existing subarrays, being pointed south-east, but will receive the least shading. I expect these effects to approximately cancel each other out, so the new panels will provide 2400/5700 as much electricity as my existing array, or slightly under 3MWh per year.


The expansion ended up being much cheaper than I expected - under $1 per watt, including the price of steel mesh around the panels to keep squirrels out! It is eligible for the federal investment tax credit (ITC) but not for my state-level incentives because it does not include a new inverter. The addition of this cheap capacity brings down the overall system's cost per watt by over 15%.

$3,300Base price for 2400Wdc upgrade$1.37/W
($990)Federal tax incentive (ITC)$0.41/W
$2,310Actual upgrade cost$0.96/W
$12,673Original system cost$2.22/W
$14,983Total expanded system cost$1.85/W


The electricity generated by these new panels should be worth roughly $530/year, for a payback period of between 4 and 5 years. The payback period of the full system should drop from about 10-11 years to 8-9 years as a result of this expansion.

Version 0.2     |     Originally written: August 18, 2018     |     Latest revision: June 8, 2019     |     Page last generated: 2024-06-08 08:09 CDT