Corrections Log: Every Factual Fix, Dated
This is the public record of factual corrections on SolarCostData. Each entry gives the date, the pages affected, what was wrong, and what changed. Fixes are made at the source — the data file or the generator that builds the page — so a corrected figure cannot reappear on the next rebuild. The policy behind this log is on the about page ; to report an error, use the contact page .
2026-09-19 (night)
- State page calculator contradicted the headline (50 pages). The embedded solar calculator opened on a $180 default bill, so /solar-panel-cost/texas/ said “10.7–21.0-year payback” in the headline and “~9.9 years” in the calculator; the calculator also omitted the running costs and inverter replacement the headline model includes. Fixed: the default bill is derived from the page’s own 8 kW, yield and rate, the calculator now carries the same $150/yr running cost and year-14 inverter replacement, the export-rule select offers the range’s high end where the page shows a range, and a deploy gate evaluates all 50 pages headlessly and fails the build if the default result differs from the headline by more than 0.1 years.
- Empty amber warning bars on every calculator. A soft-cap warning element was inserted after each number input with visible padding and a dark-theme text colour, leaving 4–9 empty bars per page. Fixed: the element is created only when there is a message, with light-mode colours.
2026-09-19 (evening)
- Degree-days on the appliance-by-state pages (120 pages) and the 20 winter state pages. The pages cited EIA STEO Census-division degree-days as if they were state figures — “Maine’s heating degree-days (5,608)”, “Minnesota’s (5,051)” — which are the New England and West North Central division totals and inverted reality (Minnesota is colder than Maine). Fixed: the hours model now uses NOAA Climate Prediction Center state population-weighted degree-days (Maine 6,471, Minnesota 6,878 HDD for October 2025–March 2026, against a CONUS 3,500); every state-level figure is labelled “NOAA CPC state population-weighted HDD/CDD”, the division series is kept only for the forecast table and is labelled literally as “EIA STEO
census division degree-days”, and Alaska, which NOAA’s CONUS file does not cover, uses the division figure with that label and a caveat. Hours, season costs and titles were recomputed on all 120 pages.
2026-09-19
- Utility-dependent export regimes (Texas, Tennessee, Wisconsin, Alabama). The solar calculator preset and the state and city pages modeled full-retail export credit for states that have no statewide rule, while the net metering table correctly said Texas has no state requirement and retail-provider buyback plans pay around 3¢/kWh. Fixed: every surface now shows a payback range from full-retail to the reduced credit (3¢ where EIA/PUC-published, otherwise 30% of retail) with the caveat “export rule not verified with your utility”; the calculator preset labels the same range.
- US-average denominator on electricity rates by state . The “% vs US average” column divided by 18.30¢; EIA’s June 2026 US total is 18.34¢. Fixed: the denominator is now read from the EIA data file, and the CSV column is named accordingly.
- “2026 US average” label on the 17¢ default rate. Appliance and EV pages described 17¢/kWh as the 2026 US average; it is EIA’s 2025 full-year residential average (June 2026 monthly: 18.34¢). Fixed: relabelled sitewide.
- Net metering source links. 30 of 52 rows on the net metering table had an empty source link. Fixed: rows without a primary PUC or utility URL on file now link to the DSIRE state program list; a real primary URL replaces it as each is verified.
- Heat pump crossover preset (Carrier 38MARBQ24AA3). The unit’s listed 5°F COP (2.21) exceeded its 17°F COP (1.98); NEEP publishes only its 5°F max-speed COP, so the curve could not be stated on the same basis as the other units. Fixed: the record was removed; seven named NEEP units remain.
- Freshness metadata. Article JSON-LD carried a datePublished equal to the build date, and a pre-heading “Data refreshed” bar could differ between cached copies. Fixed: datePublished is a stored first-publish date, dateModified comes from the content manifest, one visible “Updated” line remains, and calculator/data pages carry Dataset, Breadcrumb and WebApplication schema rather than Article.
- Appliance ranking wording. Pages ranked 5–8 of 40 described themselves as “mid-table”. Fixed: the band logic now says “top quarter” for ranks 5–10.
- Winter state page template. Sibling pages shared up to 74% of their text. Fixed: the template was rebuilt around each state’s own numbers (utility table, worked formulas, degree-days); the worst pair is now 64% and a uniqueness gate blocks regressions.
Sources: U.S. Energy Information Administration (EIA) electricity rates · DSIRE incentive records · public IRS/OBBBA guidance. Figures are modeled estimates, not quotes or tax advice. See our methodology.