Sources and Data Updates
Every default number in our calculators is sourced from primary government and research benchmarks with explicit dates checked.
Energy and Weather Data
- Solar Radiation & Weather: National Renewable Energy Laboratory (NREL) PVWatts v8 API and TMY3 (Typical Meteorological Year) datasets.
- Electricity & Natural Gas Rates: US Energy Information Administration (EIA) Electric Power Monthly state retail averages and NREL OpenEI Utility Rate Database.
- Heating Fuel & Propane: US EIA Weekly Heating Oil and Propane Program (SHOPP) benchmark pricing.
Loans and Real Estate
- Mortgage Rates: Federal Reserve H.15 Selected Interest Rates and Freddie Mac Primary Mortgage Market Survey (PMMS).
- Private Mortgage Insurance (PMI): Consumer Financial Protection Bureau (CFPB) Homeowners Protection Act statutory guidelines (80% borrower request, 78% automatic termination).
- Vehicle Operating Costs: EPA Fuel Economy Guide and AAA Your Driving Costs annual benchmarks.
Statutory Tax Credits and Incentives
All federal clean energy and vehicle incentives reflect current statutory law and Internal Revenue Service (IRS) guidelines:
- Section 25C (Energy Efficient Home Improvement Credit): Defaulted to 0% following expiration under Public Law 119-21 (One Big Beautiful Bill Act) for equipment placed in service after December 31, 2025.
- Section 25D (Residential Clean Energy Credit): Modeled per statutory phase-down schedules for solar and storage systems.
- Section 30D / 25E (Clean Vehicle Credits): Updated to reflect post-2025 termination rules.