Educational reference
Solar Data Sources
Solar production, electricity-rate, ZIP-centroid, policy, refresh-cadence, and privacy documentation for Power Totals solar calculators. The methods, assumptions, sources, and review dates are stated in the page so each figure can be interpreted in context.
Solar production, electricity-rate, ZIP-centroid, policy, refresh-cadence, and privacy documentation for Power Totals solar calculators.
How the solar data works
Scheduled builds fetch public NLR, EIA, and Census 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 calculator math without sending a lookup to those source agencies. Quote requests, email subscriptions, analytics, and related data collection are separate and described in the Privacy policy.
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 its recorded source check. No incentive is auto-applied.
Federal policy snapshot: . 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 snapshot .