Changelog

This is the record of substantive change: new sections, data updates, and changes to how the site works or what it promises. Factual errors that reached you are recorded separately, in the corrections log.

Each living page also carries its own change history, so you can see how a particular answer has moved over time without reading this whole list.

2026

20 August, later

1,356 place pages, and the finding that undermines them. Every place page carries a PVGIS run for that place’s own postcode centroid, its own monthly profile, its rank against every other place we model, and the cost published for its own region — 995 towns and all 361 UK council areas, with regional summaries and a league table.

The honest headline is on every one of them: the spread from the sunniest place we model to the least sunny is about 54%, while turning a roof from south to north costs far more. Your postcode is not the question; your roof is.

Find your network operator — the 14 GB licence areas plus Northern Ireland, with Distributor IDs so you can confirm yours from the MPAN on your bill. Operator contact details are deliberately absent: the document that lists them is four years old and 105 works.

The Warm Homes: Local Grant, and which councils are in it. This is the one scheme that pays for solar outright — Solar PV is on its list of eligible measures, a battery is permitted alongside, and delivery closes 31 March 2028. The award list is published as structured data rather than a table; we parse it, and because consortium members are named, 277 councils are covered. Every council page now says whether that authority appears.

Panels, inverters and batteries — and an explanation of the database we are not building. MCS holds the certification records for over 330,000 products and its terms prohibit copying or redistributing them, so instead of a comparison table built from someone else’s data we published how to read a panel datasheet, an inverter specification and a battery specification — the documents MCS’s own installation standard says you must be given before you sign.

A fix worth recording. The section sidebar listed every sibling page, which on a thousand-page section meant 107 kB of links on every page. It is now capped, which took the built site from 191 MB to 76 MB.

20 August

New builds cluster opened. The Future Homes Standard, read from Approved Document L Volume 1, 2026 edition and SI 2026/335 rather than from coverage of them: the 40% ground floor area rule, the timeline and key dates, and what to ask when buying a new build.

Two things the coverage generally gets wrong, and this cluster does not. The 40% is not a coverage requirement — it describes a notional array on a south-facing 45-degree unshaded roof, and the rule is to match that array’s annual output, so a worse roof needs more panels rather than fewer. And the transitional arrangements matter more than the headline date: a home whose building control application went in before 24 March 2027 and which commenced before 24 March 2028 may lawfully have no solar at all.

Three more new-build pages, on the questions the regulations leave open: who owns the panels, whether the developer’s system is any good, and upgrading one. The useful number in there is 3.68 kW — the largest registered capacity inside the simpler G98 network process, and below the target capacity the 40% formula produces for most houses. What inverter a developer fits therefore decides how much you can add later.

Five glossary terms added with the sources read and dated: Future Homes Standard, requirement L3, BREL report, ground floor area, higher-risk building.

A gap closed rather than left open. Solar on new build homes said in August that we could not describe the building regulations requirement because we had not read the documents. We have now read them, and the page says so and links to the cluster.

20 August

The costs section opens, with real prices. For months this site has declined to print a solar price because we had no source we trusted. We now do: Solar photovoltaic (PV) cost data, an official statistics series that DESNZ derives from the MCS Installation Database — prices actually paid for certified installations, not prices advertised, published under the Open Government Licence.

Four pages built on it: the hub, cost per kW, thirteen years of price history, what is actually in a quote, and the costs that are not in the headline. Every figure on them is generated from the dataset by a shortcode rather than typed, so they cannot drift out of step with it.

Three things the data shows that the folklore does not. Solar is barely cheaper than it was in 2013 in cash terms — £1,897/kW then, £1,780/kW now, having peaked 53% higher in 2023/24. Bigger is cheaper per kW, because much of the price is fixed rather than per-panel. And new build installations cost about 17% less per kW than retrofits, which is the evidence for a claim we had previously made without it.

Cost by system size, eleven pages, from 2 kW to 20 kW. Generated by a script so the prose is per-size and the numbers come from the datasets at render time — no page hard-codes a price.

Payback, with the assumptions visible. The payback page shows a grid rather than a number: nine years to twenty-six on the same 4 kWp system, depending only on self-consumption and export tariff. Are solar panels worth it takes the same arithmetic and says plainly which households it does not work for.

Four new calculators, all running in your browser with nothing sent to us: how many panels do I need, roof area to system size, export earnings and battery sizing. The export one ranks every open untied tariff against your own surplus — on a typical 4 kWp system the gap between the best and the median rate is over £200 a year.

The battery calculator deliberately stops short of payback, and says why: our cost pages rest on an official statistics series for solar, and no equivalent exists for storage. It does the sizing arithmetic — bounded by daily surplus and by evening demand — and leaves the number we cannot source unprinted.

The economics set, modelled rather than asserted. ROI and IRR puts a median-priced 4 kWp system between −0.8% and 9.4% a year over 25 years — the same panels, the same roof, the same price, with only self-consumption and export tariff changing. Solar against a savings account works the comparison through, including the point most versions miss: avoided spending is not taxed the way interest is. What price makes solar stop making sense asks the question the industry never asks, and finds that a low self-consumption household on the median export rate is already below break-even at today’s cap. Does solar reduce your bill or your consumption explains why the bill falls by less than the generation suggests.

The new builds cluster is finished — self-builders and the heat pump package complete it, apart from a developer-by-developer comparison that stays unbuilt until specifications can be sourced.

How to pay for it, and the traps. How to pay for solar compares cash, card, regulated credit, buy-now-pay-later and mortgage borrowing on protections rather than rates — section 75 joint liability, the section 66A 14-day withdrawal right, and what you give up when a debt is secured on your home. Solar finance: the traps sets out the mechanisms, and green mortgages covers borrowing against the house.

One dated change worth knowing: buy-now-pay-later becomes regulated on 15 July 2026 under the FCA’s PS26/1. Anything written on that before this year is out of date.

VAT has a deadline. HMRC’s guidance is that installation reverts from zero-rated to 5% on 1 April 2027. On a median 4 kW system that is about £320.

The devolved standards are not the same standard. Wales, Scotland and Northern Ireland sets out four different positions: Wales requires on-site renewable generation from 4 March 2027, three weeks before England; Scotland requires nothing of the kind; Northern Ireland proposed something in 2023 and has not enacted it. This page carries more “we could not establish” than any other on the site, because gov.wales blocked us and we would rather show the hole.

18 August

Plug-in solar cluster finished. The post-legalisation pages, written from the statutory instrument, the specification and the government response rather than from coverage of them: SI 2026/848 explained, the regulatory timeline, the buying guide, mounting, why batteries stay excluded, and Germany’s experience.

Two findings worth flagging from that reading. The law names version 2 of the specification, published 16 July 2026 — not “the specification” as a living document, so a later version would not automatically become the one the regulations point to. And regulation 3 does not extend to Northern Ireland, because the instrument it amends does not apply there.

Buyer protection cluster published. Eighteen pages on the part of solar where people actually lose money: cancellation rights, section 75, what to do when an installer goes bust, checking an installer, what a good quote looks like and the rest.

Property cluster published. Seventeen pages covering the transactions and building types general guidance skips — buying and selling a house with panels, rent-a-roof leases, flats, leasehold, and the roof types.

Planning cluster published. Thirteen pages, including the 200 mm projection rule, Article 4 directions and right to light.

Two templates published as free PDFs. A conservation area application template with a worked heritage statement, and a quote checker whose location and orientation tables are generated from our own dataset rather than typed. No sign-up for either.

A build gate added after making the same mistake three times. A stray closing shortcode inside another shortcode rendered without complaint in Hugo, so the build stayed green while the markup was wrong. There is now a check that every paired shortcode opens and closes the same number of times, and it runs with the tests.

17 August

Grid connection cluster published. Five pages covering the part of UK solar that is most technical and worst served: G98 vs G99, how to apply for a G99 connection, export limiting, what happens if your DNO refuses, and what MCS is. Written from the Energy Networks Association’s own engineering recommendations, read in full.

Generation dataset published as an open download. All 625 modelled values — 25 locations, five pitches, five orientations — as a CC BY 4.0 CSV. No sign-up, no email address. The /data/ section opened to hold it.

Fundamentals cluster published. Nine pages on the things that actually decide whether solar works on a particular house: kWp vs kWh, irradiance, self-consumption, shading, roof orientation and pitch, east–west versus south, north-facing roofs, and generation by region.

Rule 7 added. Cite the issue number and the document’s own internal date, never just the URL. Added after finding we had cited a superseded standard across nine pages. See methodology and the correction.

Both calculators’ self-consumption defaults replaced with sourced figures. This materially reduced the savings they report. Logged as a correction because the old figures were live.

Citation practice changed for restricted sources. Where a document is free but behind a registration wall, or where we read a freely available copy rather than the publisher’s gated one, the citation now says so. You should know what a source will ask of you before you click.

16 August

SEG tariff table published. Every export tariff in Ofgem’s latest annual report, untied tariffs first, open before closed, closed ones struck through rather than hidden. Built from Open Government Licence material, so it is republished in full rather than summarised.

SEG change monitor started. A daily job that detects when the published tariff landscape moves. It stores a hash rather than a copy, because detecting that a page has changed engages neither copyright nor database right.

Grants hub published. What actually pays for solar, grouped by whether a scheme funds solar PV at all — including the schemes that appear on every roundup and never covered it.

Rooftop calculator published. Generation and value split into what you use and what you export, because those are worth very different amounts and that difference is what most calculators hide.

15 August

Plug-in solar cluster completed. Twelve pages covering the regulatory position, the 800 W question, G98 notification, insurance, renting, leasehold, fire safety, conservation areas, and an honest comparison with rooftop solar.

Downloadable letter templates published. Free, ungated, traceable clause by clause: a tenant’s request for consent, a leaseholder’s request for freeholder consent, and a pre-installation checklist. This became rule 6 — where a page tells someone to write a letter, we write the letter.

Generation dataset built. 625 PVGIS model runs at the loss factor MCS specifies, so that every figure on the site traces to a model we ran rather than a table we copied.

13 August

Site launched. Foundation, page templates, glossary mechanism and the trust furniture — verified dates, source lists, corrections notices. Initial policy pages published: about, privacy, terms, cookies, accessibility, methodology and sources.

Errors caught in review

Not corrections, because they never reached you. Recorded because the checks that catch them are part of how we work, and because a site that only publishes the mistakes that escaped gives a misleading impression of how many it makes.

17 August. A dataset minimum quoted as 181 kWh/kWp when the true value was 157 — we had read the last row of a file as the smallest. A year-to-year variation range given as 2.4–3.7% when the data said 2.4–4.1%, with a tidy explanation attached about northern locations being steadier that the data flatly contradicted. A comparison table that rendered its headline UK figure as zero because of a template bug. All three were caught by checking prose claims against the underlying datasets before publishing.

17 August. A page criticising others for citing superseded standards was itself carrying a citation we could not confirm was current. Rather than quietly linking to something newer, the page now states what we read, what we could not check, and why.

What goes where