Corrections

When we get something wrong we do three things: fix the page, put a dated note at the top of it, and record it here. We do not quietly edit.

Where an error affected a figure someone might have acted on, the entry says what the figure was, not only what it should have been.

Log

17 August 2026 — our calculators overstated self-consumption, and therefore the saving

Affected: the rooftop calculator and the plug-in solar calculator.

What was wrong. Both calculators asked you what share of your generation you would use yourself rather than export, and both defaulted to a range we had chosen: 25–60% on the rooftop calculator and 50–90% on the plug-in one. Both were labelled as our assumption rather than a sourced figure, which was honest as far as it went. It did not go far enough.

When we read MCS’s guidance note MGD 003 properly, we found the authoritative UK method gives substantially lower figures. For the rooftop calculator’s own default scenario — a household using 2,500 kWh a year with a 3,676 kWh array — MGD 003 gives 23% if someone is home all day, 19% if the property is empty half the day, and 14% if it is empty on weekdays. The bottom of our old range sat above the top of theirs.

What we changed. The rooftop calculator now defaults to 14–23% and the plug-in calculator to 40–56%, both taken from MGD 003 for the relevant generation and consumption, and both labelled with where they come from. We also published the page explaining the method and why the figure matters more than anything else on a quote.

Why it matters. Self-consumption is the single biggest lever on what solar is worth, because a unit you use is worth roughly six times a unit you export. Our old defaults made systems look better than the evidence supports. The corrected figures reduce the headline saving our own calculator reports, which is the direction an honest correction usually goes.

17 August 2026 — nine pages cited a superseded version of MIS 3002

Affected: the plug-in solar cluster and both calculators.

What was wrong. We cited MCS MIS 3002 as issue 5.0 throughout. It is now issue 6.0, dated 18 March 2026, published at a different address. The old PDF is still online and still resolves, so nothing broke and nothing announced itself.

What we changed. Every citation now names issue 6.0 with its internal date, and we re-read the standard rather than assuming continuity.

What we did about the cause. This produced rule 7: cite the issue number and the document’s own internal date, and trust the number printed inside the document over the filename or the folder. We had also been citing the 2019 issue of MGD 003, which sits at a newer-looking URL than the current 2022 issue — the same trap, twice, in one afternoon.

17 August 2026 — our link to the G98 standard had quietly stopped working

Affected: do I have to tell my network operator about plug-in solar?

What was wrong. Our citation pointed at an Energy Networks Association URL that had begun redirecting to a generic publications index. The link resolved, so no checker flagged it, but it no longer reached the document.

What we changed. Citations now point at the freely downloadable copies on the GB Distribution Code site, where we read the documents, with ENA’s own database named as the publisher’s index and flagged as requiring registration.

17 August 2026 — an arithmetic slip repeated on two pages

Affected: plug-in solar or a proper roof system? and the rooftop calculator.

What was wrong. We gave annual generation for a 4 kWp array in London as 3,674 kWh. Our own published dataset gives 919 kWh per kWp, so the figure is 3,676 kWh. The error came from multiplying an unrounded intermediate value instead of the number we publish, so our prose disagreed with our own calculator by 2 kWh.

What we changed. Corrected to 3,676, and the range across our 25 locations from “2,770 to 4,169” to 2,768 to 4,168.

Why we are logging something this small. Because the whole claim of this site is that you can check our working. A figure that does not reconcile with our own published dataset undermines that whether the gap is 2 kWh or 200.

15 August 2026 — we framed the 800 W limit as per circuit before that was settled

Affected: the plug-in solar cluster.

What was wrong. We described the 800 W limit as applying per circuit. The government response is more conditional than that: the change is stated to be subject to a corresponding amendment to G98, and until that amendment is made the existing requirement limiting installations to one device per household continues to apply.

What we changed. Every affected page now gives the one-per-household position as current, with the per-circuit change described as pending the G98 amendment, and a dated status box saying so.

Why it matters. Someone acting on the earlier framing could have installed a second device believing it permitted.

Caught before publication

These did not reach you, so they are not corrections. We mention the category because the checks that catch them are the same ones described in our methodology, and because a corrections page that only lists what escaped gives a misleading impression of how often we are wrong.

Recent examples: a dataset minimum quoted as 181 kWh/kWp when the true figure was 157; a year-to-year variation range given as 2.4–3.7% when the data said 2.4–4.1%, attached to a tidy explanation about latitude that the data did not support; and a table that rendered a headline figure as zero because of a template bug. All three were caught by checking prose claims against the underlying data before shipping. They are recorded in the changelog.

Reporting an error

Please include a link to the page and the specific claim you think is wrong. If you have a source, even better.

Report a correction

What counts

We log:

• factual errors — wrong figures, dates, rules or names of schemes
• material omissions that made a page misleading
• calculations that produced the wrong result
• broken or misattributed sources, including citations to superseded versions

We do not log typographical fixes, rewording, or routine updates where a figure changed because the world changed rather than because we got it wrong. Those appear in the changelog.