Last reviewed: 3 September 2026.
This page describes how the content on this site is produced, checked and updated, so
that you can judge how much weight to give it. It is deliberately specific, including about our
limitations.
1. Sources, in order of preference
- The legislation itself, from
legislation.gov.uk.
For plug-in solar that means SI 2026/848 rather than anyone’s summary of it. - Government publications on GOV.UK — the DESNZ consultation response and Interim
Product Specification, HMRC VAT notices, and departmental guidance. - Regulators and industry bodies — Ofgem for prices and the Smart Export
Guarantee, the Energy Networks Association for G98 and network operators, MCS and RECC for
certification. - Published market data, clearly attributed, for things no official body
publishes — such as retail prices of kits and installed battery costs. - Our own measurements and surveys, when we have them, always dated.
We do not cite other blogs as authority for a rule. If a number can only be traced to another
content site, we treat it as unverified and label it.
2. What we do when we cannot verify something
We say so on the page, in the place where the number would have gone. There are live examples: the
detailed electrical thresholds in the DESNZ Interim Product Specification are widely quoted in trade
coverage, and we have not yet been able to extract them from the official document, so we describe
that the requirements exist without repeating figures we have not seen at source. That is
deliberately less satisfying than a confident number and it is the correct thing to do.
3. Dates on everything
Every page carries a “last reviewed” date. Every figure in pence or pounds carries the period it
belongs to. This matters more here than in most subjects because three separate clocks are running:
- The Ofgem price cap changes every three months, on 1 January, 1 April, 1 July
and 1 October. Every savings figure on the site is rewritten when it does. - The zero rate of VAT on home batteries is due to end on 31 March 2027, and the
zero rate on domestic electricity on the same date. Both are reviewed after every
Budget. - The product specification is interim and will be replaced. When it is, the
affected pages are rewritten rather than patched.
4. Our own estimates, labelled as such
Some things we need for a calculator have no citable public source at the granularity we want —
regional yields per kilowatt-peak, orientation and mounting factors, typical self-consumption shares.
Where that is the case we use rounded estimates derived from published ranges, we state the number
we used, and we label it as our estimate rather than dressing it up as an official figure. Our
calculators list every assumption on the page beside the result.
5. What we do not have
- No technical reviewer. No page here has been checked by an MCS-certified
installer, an electrician or a chartered engineer. Many sites imply otherwise with a vague “reviewed
by our experts”; we will not, and if we ever engage a reviewer we will name them and their
qualification. - No laboratory testing. We have not tested a kit to destruction and do not claim
to have. - No legal or tax qualification. We describe rules and point to the bodies that
administer them.
6. Corrections
Substantive factual corrections are made on the page and noted, not slipped in silently. Typos and
formatting are fixed without ceremony. If you spot an error, the
contact page goes straight to the person who wrote it.
7. Independence
No advertiser, manufacturer or retailer sees content before publication, influences a ranking, or
pays for a mention. The site does not yet earn anything: it carries no advertising and no affiliate
links. How it is intended to make money, when it does, is explained on
how we make money. Where a conclusion is against our commercial
interest — for example, telling a reader that a plug-in kit will not pay on their shaded north-facing
balcony — we publish it anyway, because a site that cannot do that is worth nothing to read.