Assumes $900 to install one 325 W panel — hardware, mounting, microinverter, electrical work, labour and permitting — repaid only by the electricity it avoids buying. No subsidies, tax credits, net-metering premium, financing cost or future price rises are counted, and the figure is undiscounted. Electricity price is the IL residential average (EIA, May 2026). A single panel is unusually expensive per watt because it carries a whole array's fixed costs, which is why these numbers look worse than rooftop solar generally does.
| Buildings with roofs | 5,719,218 |
| × Panel rating | 325 W |
| × Annual yield per panel here | 401.8 kWh |
| Annual generation | 2,298,209,751 kWh |