How RayCalc Calculates Results

Transparency about our formulas, data sources, and limitations.

📐 Formula

Annual savings = (system size in kW × average daily sun hours × 365 × electricity rate) × panel efficiency factor. Payback period = total system cost ÷ annual savings. Federal tax credit (30%) applied to system cost.

📊 Data Sources

NREL (National Renewable Energy Laboratory) solar irradiance maps; EIA (Energy Information Administration) state electricity rates; DSIRE database for state/local incentives.

⚠️ Limitations

Assumes south-facing roof with standard tilt. Shading, roof age, and local permitting not factored. Electricity rates and net metering policies may change. Get multiple installer quotes for firm pricing.

🕐 Last Reviewed

June 2026. Methodology is reviewed quarterly and updated when underlying data sources or industry standards change.

🚫 Disclaimer

This tool provides estimates for informational purposes only. Results are not financial, legal, or professional advice. Always consult qualified professionals and obtain multiple quotes before making decisions based on these estimates.