The changelog of Solar Panel Cost Calculator lists every dated change to its calculators, data and pages, newest first. No entry has been logged yet. You are looking at method version 1.0, with data last refreshed on 14 November 2026. Each entry says what changed, why, and what it did to the reference home: a 4 kWp south-facing system on a typical home.

Current version
Field	Value
Method version	1.0
In use since	14 November 2026
Data last refreshed	14 November 2026
Reference home now	Installed cost £8,400, yearly saving on bills £193.45, export income £407.81 a year, payback 14 years
Last correction	None logged

The formulas behind this version are set out in our Methodology. The fields are explained under how to read an entry.

All Changes, Newest First

No entry has been logged yet. Entries will appear here newest first, grouped by month, and each one keeps a fixed address on this page.

The first entry will record the first public version of our calculators. It will give the date, the method version, the datasets loaded with the period each one covers, and the starting figures for the reference home.

Corrections

No corrections have been logged. How we check a report and fix an error is set out in our editorial policy and corrections rules.

A correction is an entry in which we were wrong. When one is logged, this section lists its date, what was wrong, what the figure is now and the pages it touched. The corrected page also shows a "Changed on" note with the date.

Changes We Know Are Coming

Some changes have fixed dates, so we list them before they happen. The table gives five scheduled changes, each with what we will update and the body that sets the date.

Scheduled changes
Date	What changes	What we will update	Source
1 April 2027	VAT on solar panels and batteries fitted in a home rises from 0% to 5%	Every installed price, recalculated at 5%	HM Revenue and Customs (HMRC), VAT Notice 708/6
1 April 2027	The next Ofgem price cap quarter starts	The electricity unit rate and the standing charge	Ofgem
1 July, 1 October and 1 January after that	Each later price cap quarter starts	The electricity unit rate and the standing charge	Ofgem
30 June 2027	The temporary 0% VAT on household electricity in Great Britain ends	The unit rate, once HMRC confirms the rate that follows	HMRC, VAT Notice 701/19
Not announced yet	The Department for Energy Security and Net Zero (DESNZ) publishes its next yearly "Solar PV cost data"	The installed cost per kW for each size band	DESNZ. The latest release is dated 28 May 2026

Our prices use 0% today, which is the VAT rate for solar panels and batteries in a home until 31 March 2027. Each dataset's own release cycle is listed in our sources and data log. When a row's date passes, the change becomes an entry above.

How to Read an Entry

Each entry has a type, a date, the version it produced and its effect on the reference home. The table sets out the seven entry types and what each does to the method version.

The seven types of entry
Type	What it covers	Does the version change?
Method	A formula, a default or a verdict limit changed	Yes. The first number goes up
Correction	We fixed a wrong figure, date, rule or name	The second number goes up when results change
Data refresh	A dataset owner published new figures, such as a price cap quarter or a DESNZ release	No. The data stamp changes
Rule or scheme change	A tax, grant, export or grid rule changed	Only when a formula changes, as it does with a VAT rate
Page update	The answer or advice on a page changed without a formula change	No
Accuracy check	A test run of the calculator against the reference home, with its result	No
Policy, consent and partner terms	A new version of the privacy notice, the cookie policy, the consent wording or our arrangement with Leads 2 Trade	No

Each entry is written in the same order, so two entries can be compared field by field:

Date: the day the change went live.
Type: one of the seven in the table.
Method version and data stamp: both as they stand after the change.
Title: one plain line that says what changed.
What changed: the old value and the new value, with the unit and the source.
Why: the source published new data, a rule changed, or we found or were told of an error.
Effect on the reference home: installed cost, yearly saving on bills, export income and payback years, before and after.
Pages affected: the pages where a figure or the text changed.

The reference home is one fixed case that we run on the old and the new version: a 4 kWp south-facing system with no shade and no battery, on a home that uses 2,500 kWh a year and is out most of the day. It has no postcode, so it uses our stand-in yield of 968.01 kWh per kWp. An entry that leaves it untouched says "No effect on the reference home" and names the inputs that are affected.

How Our Version Numbers Work

Our method version has two numbers: the first changes when a formula, default or verdict threshold changes, the second when a correction changes results for some homes.

A data refresh keeps the version and changes the data stamp. That lets you tell "same method, newer data" from "new method". The Methodology page and this page read the method version from the same place. If the two ever differ, that is an error, and we log it.

What We Log and What We Do Not

We log every change that alters a figure, a date, a rule, a verdict or the advice on a page. Eight kinds of change always get an entry:

Formulas.
Defaults.
Verdict limits.
Dataset refreshes, every one.
Corrections, however small.
Changes to scheme rules or dates.
New pages that add a calculator.
New versions of policy and consent wording.

Three kinds of change get no entry, because they alter no figure and no meaning:

Spelling and layout fixes.
Image swaps.
Link fixes.

We never delete an entry and never back-date one. A wrong entry is corrected by a new entry that points back to it.

Report Something We Got Wrong

If a figure, date or rule on this site looks wrong, tell us and we will check it against its source. A report moves through three steps:

Email [email protected] with the page address, the figure and the source you think is right.
We check the figure against its source and reply within 2 working days.
We fix a confirmed error, add a "Changed on" note with the date to the page, and log the fix here.