How the solar calculator works
The math chain
Bill ÷ rate = monthly kWh. Panels needed = monthly kWh ÷ (30 × sun-hours × panel kW × 0.8 system efficiency). The 0.8 covers real-world losses: inverter conversion, wiring, soiling, panel aging, and the fact that roofs are never perfectly oriented. A $150 bill at 16¢ is 940 kWh/month; at 4 sun-hours with 400W panels that's about 21–22 panels — a ~8.5 kW system.
What the estimate costs (2026 ballpark)
US residential solar installs run roughly $2.50–3.50 per watt before the federal tax credit (30% through 2032 under current law, subject to change — verify). Our 8.5 kW example: ~$21–30k gross, ~$15–21k after credit, against ~$1,800/year of offset bills — commonly a 8–12 year payback with 20+ year panel life. State incentives, net-metering policy, and your roof's shading can each move this a full payback bracket in either direction.
What this estimate can't see
- Roof geometry: orientation, pitch, shading, and usable area gate the panel count the roof will actually take.
- Your utility's policy: net metering terms decide what excess production is worth — the single biggest local variable in solar economics.
- Consumption trajectory: an EV in the garage or a heat-pump conversion changes the target. Size for the house you'll have, not the one you audit.
Use this number to speak installer fluently: "My usage is X kWh, I'm looking at Y kW, what's my production estimate?" — then collect three quotes and make them justify the spread.