We compare the job a system must do before comparing products. Every model claim should trace to a current maker document, an official source or a clearly identified independent reference.
Our evidence order
We prefer regulations and official scheme pages for rules; current technical sheets and installation manuals for product specifications; and established independent energy organisations for general guidance. Retailer summaries do not establish a technical fact.
How calculators work
Inputs are visible and editable. We avoid hidden national averages where a reader can use their own tariff or demand. Results state what is excluded and should never be read as a quote or savings guarantee.
What “best” would require
A best-product comparison must name its criteria, verify current availability and use comparable test conditions. Until that work is complete, we publish a buying method rather than a ranking.
Corrections
If evidence changes, we update the page date and source record. Material corrections will be explained on our corrections page.