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Here's my payback calculations based upon the ave. monthly (3 yr ave) energy my system (3.45kW) produces. The 1st couple of years besides savings from Nat Grid on my electric, I could sell REC credits, originally they were $0.06 KWH but 2 years ago the price dropped to $0.03 KWH and I didn't renew the contract however for this example I have left them in.
When I first did the calc. the fully burdened costs was $0.12348 KWH (red), check this month's bill it is already up to $0.1784 over the last 5 years, what will it be 20 yrs from now? Table show another 3X increase. This is a very simple analysis just assuming you pay the same KWH rate the entire time vs. amortized in any way.
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