Annual usage is estimated from your bill and electricity rate. With a valid ZIP, production is modeled using NLR PVWatts V8; otherwise the calculator uses a state-level planning factor.
Local energy data
Utility & Incentives by ZIP
Find nearby residential utility plans, distributed-generation rules and active solar incentives before we model the tariff in the savings engine.
How Calculator v3 works
- A valid U.S. ZIP code is converted to approximate latitude and longitude using postal-code location data.
- Those coordinates, roof tilt and direction are sent server-side to National Laboratory of the Rockies PVWatts V8 to estimate production for a 1 kW reference system.
- The returned kWh-per-kW yield is used to size your system for the selected percentage of annual electricity use.
- Residential electricity prices start with U.S. EIA Electric Power Monthly, Table 5.6.B, Year-to-date through June 2026, and remain editable because individual utility tariffs vary.
- The local-data module queries OpenEI's U.S. Utility Rate Database for nearby residential tariffs and OpenEI for active residential renewable-energy incentives.
- Complex utility tariffs are shown as reference data first. We do not automatically replace the calculator's all-in electricity rate until the tariff engine can model TOU, tiers, fixed charges and export compensation correctly.
- If PVWatts, OpenEI or ZIP lookup is unavailable, the core calculator automatically falls back to our state-level planning data instead of failing.