Data Sources & Methodology
Data last updated: January 2025 · Updated annually for costs and incentives, monthly for electricity rates
How the Numbers Work
System size (kW) = annual kWh usage / (location peak sun hours x 365 x 0.8 derate factor). System cost = size x state average installed cost per watt, minus federal credit (30%) and applicable state incentives. Annual savings = (system kWh production x electricity rate) less any grid fees. Payback = net cost / annual savings.
Data Sources
NREL National Solar Radiation Database
National Renewable Energy Laboratory's irradiance data covering solar resource levels by location. The foundation for production estimates.
EIA State Residential Electricity Prices
Monthly electricity rates by state. Higher rates mean faster payback. Updated monthly.
SEIA Solar Installation Cost Data
Solar Energy Industries Association annual average installation costs per watt by state. Tracks how installed costs have trended.
DSIRE Incentive Database
Database of State Incentives for Renewables and Efficiency. Source for state and local rebates, net metering rules, and additional incentives.
IRS Form 5695
Federal residential clean energy credit (30% of system cost under current law through 2032).
Limitations
Production estimates use average irradiance for your area. Actual production depends on roof pitch, shading, panel orientation, and system degradation (0.5-0.8% per year). Net metering rates vary by utility and can change. Some utilities have demand charges that reduce the value of exported power. Battery storage is not included in payback calculations.
About Estimates
The numbers on this site are estimates built from published data. They're a starting point for budgeting and comparison, not a quote. Your actual cost depends on specifics no calculator can know: your vendor, your timing, your circumstances.
Nothing on this site is financial, legal, or professional advice. If the decision is significant, talk to a professional.
SolarBreakeven · Built in Sacramento, CA · Data updated January 2025