Corrections & changelog.
Every number on this site is published with its source and its formula, as described in the methodology. When we get one wrong, this is where we say so: what was wrong, what changed, and when, so you can open the affected guide and check. If you find an error, report it through the contact form. Substantive corrections also update the "Updated" date on the guide concerned; this log is kept by Bruno de Madrazo.
2026-09-14 — Dataset citability
Page affected: Post-Credit Solar Payback Index 2026.
- What was wrong: the dataset's version and its CC BY 4.0 licence existed only in the machine-readable schema. A reader had no plain-text way to cite the index or to know the terms of reuse.
- What changed: a visible "How to cite" block (APA and BibTeX) was added to the page; dataset version 1.0 and the CC BY 4.0 licence are now stated in plain text; the "last verified" date was aligned to the July 26 row-by-row check of the table against the CSV.
Commits 282280d (authored 2026-09-13) and 49737ee; published 2026-09-14.
2026-07-26 — Sources, numbers and the calculator
Pages affected: all 23 guides, the solar calculator, the web manifest and the social-share image.
- Sources were named but not linked. Every guide now links its "Sources" block to the actual datasets (EIA, NREL PVWatts, LBNL, ENERGY STAR, DSIRE and others). Before this change five guides had no sources block at all.
- Two incompatible sets of state electricity rates, both attributed to EIA, were in use across the site. They were unified to the single published dataset.
- The solar calculator did not reproduce the index. It now applies the same net-metering value factor as the guides, so it reproduces the index instead of diverging from it.
- Self-contradictions: the water-heater guide gave three different annual costs for the same case; the clothes-dryer guide gave two different paybacks; the California solar guide cited two different PVWatts production figures; the battery guide used an outdated Hawaii rate. Each now carries one figure, traceable to its source.
- "300+ guides" was false. The web manifest and the social image claimed it; the site has 23. Both were corrected.
Commit d7f6908.
2026-07-25 — Claims we could not back
Pages affected: phantom load, how to reduce your electricity bill, best states for solar payback, heat pump vs gas furnace, About.
- Implied measurements we did not take. The phantom-load guide spoke of "40 devices metered" and "spot checks". The figures come from the LBNL standby-power database and ENERGY STAR; the guide now says so and attributes them.
- A source that did not exist. The bill-reduction guide cited "300+ metered utility audits". There is no such corpus. The claims are now attributed to the real sources: EIA RECS, Ofgem and DOE.
- An expired credit presented as current. The same guide presented the Section 25C tax credit as available; it ended for installations in 2026. Corrected.
- Our ranking contradicted our own data. The editorial solar ranking placed Alaska in the top 10 at 9.6 years, while our own index gives 22.2 years. The ranking was regenerated from the dataset.
- Rebates that disagreed between guides. Maine and New York heat-pump rebates differed between the heat pump vs gas guide and the state rebate guide. Unified.
- Affiliate links that did not exist. The About page described them as if in place. Reworded to the future tense, which is the truth.
Commit f511679, published 2026-07-25. The affected guides carry "Updated July 23, 2026" — the day the edits were written.
2026-07-16 — Pre-review hardening
- Internal planning documents that had been deployed publicly alongside the site were removed.
- Five thin guides were expanded with state-level data: clothes dryer, phantom load, space heater, refrigerator and mini-split heat pumps.
- The two solar guides overlapped. The editorial ranking and the data study were de-duplicated and now cross-reference each other.
Commits 68b33f1, e3689ab, e764962.