Solar Data Sources

How the solar data works

Power Totals never sends a ZIP Code or calculator input to NLR, EIA, Census, or another third party. Scheduled builds fetch public source data for fixed locations, produce versioned static JSON, and ship those files with the site. The browser resolves ZIP centroids, finds the nearest fixed grid point, and performs all calculator math locally.

The current PVWatts grid is awaiting its first private-key refresh. Until that refresh, solar pages use their visible editable peak-sun-hours fallback and identify it in the result.

Production and irradiance

Source: NLR PVWatts v8. The quarterly pipeline requests a 1 kW DC, standard-module, fixed-roof baseline at 71 representative US points, with latitude tilt, 180° azimuth, and 14% losses. The client scales the result and applies visible orientation, shading, and loss adjustments. It is interpolation, not a per-address simulation.

Refresh cadence: quarterly. Last successful refresh: pending.

Electricity rates

Source: U.S. Energy Information Administration retail-sales API v2. The monthly pipeline stores the most recent residential state average in cents per kWh. It is only an editable prefill. Utility tariffs, time-of-use periods, export compensation, fixed charges, taxes, and minimum bills can differ substantially.

Refresh cadence: monthly. Last successful refresh: 2026-08-13.

ZIP centroids

Source: U.S. Census Bureau 2025 Gazetteer ZIP Code Tabulation Areas. ZCTAs are statistical areas and do not represent every USPS delivery ZIP. The entire lookup stays in the browser.

Incentives and federal policy

State and utility incentive entries are manually maintained from primary sources. The build fails when any published entry is more than 180 days past verification. No incentive is currently auto-applied.

Federal configuration verified: 2026-08-13. IRS primary guidance says Section 25D residential clean-energy credit expenditures after December 31, 2025 are not allowed. Power Totals therefore publishes no federal credit percentage and no solar tax-credit calculator.

Known limits

• Nearest-point interpolation cannot model a roof, tree, obstruction, microclimate, or utility territory.
• Actual production varies with weather, soiling, shading, degradation, mounting, and equipment.
• Economics are separate scenarios, not tax, financial, investment, tariff, or proposal advice.
• Use a licensed installer and actual utility documents for a site-specific decision.

Combined source data updated 2026-08-13.