The 8400 watt system cost about $20,000 for a DIY install. Brother is a PE, and EE with 35 years work in electrical distribution. He did hire roofers to do mounts on the roof.
From the $20,000 investment, he got a grant of $1000 from TVA and a 30% ($6000) refund from the IRS, for a net cost of $13,000. ABSOLUTELY, you can not get a payback on these systems without sucking on the government teet! Solar power can not sustain without subsidy, paid by government and other electric rate payers.
The system is producing at the rate of $2950 per year, with the $0.12 per kwh premium that TVA distributors payed on contracts made last year. Now it is $0.09 premium.
So, about a 4 1/2 year payback, counting no interest. The TVA program includes the premium for only 10 years, then you get only credit at the normal retail rate. But the system should produce for about 30 years.
His sytem is highly efficient, using the Enphase microinverter. 95% of the power produced by his 36 panels flows out to the electric system.
My system has batteries, so if the electricity goes off, I continue to have power. But payback on my system, unless you put value on that backup power, is basicly, never. Batteries cut the efficiency too much, and they won't live over about 5 years before replacement.
More later.