How we estimate
- Sunshine. Without a ZIP code, we start from your state’s average yearly output for 1 kW of panels tilted 20° toward the south (NREL PVWatts), then adjust for how your panels are mounted and which way they face. A steep balcony railing gets about 72% of the ideal; panels flat against a wall, about 65%.
- Exact estimate. With a ZIP code, we ask NREL’s PVWatts model for your location, with the tilt and direction you picked and standard 14% system losses.
- What you use. Only the power you use at the moment it’s produced lowers your bill. We assume 85% for kits up to 800 W. If your home sits empty all day with little running, lower it.
- Price. Your state’s average residential price for August 2026 from EIA. Your own bill’s price per kWh is better, especially if you’re on a time-of-use plan.
Reading the result
Payback over about ten years means the kit is mostly a hedge against rising prices rather than a money-maker. Payback under five years usually means a high-price state, good sun, or a cheap kit. Kits last 20 years or more, so even slow paybacks can come out ahead.