What the Numbers Mean

With the defaults (6 kW, 4.5 sun hrs, $0.16/kWh, $15,000 install), the system produces 21.6 kWh/day — 7,884 kWh/year, saving $1,261 annually. After the 30% ITC, net cost is $10,500, so the payback is about 8.3 years — with roughly $21,000 of net savings over 25 years and 79 tons of CO₂ avoided.

Beyond Simple Payback

This model assumes flat production and a fixed rate. Real payback is usually faster: electricity rates historically rise, and net metering credits production at retail rates. State rebates and SRECs can shorten the period further, while shading and roof orientation can lengthen it.