01
Source hierarchy
We prioritise legislation, government and regulator pages, formal technical standards and scheme operators. Commercial sources may help describe products but are not treated as independent performance proof.
02
Calculation policy
Every calculator shows its inputs and important assumptions. Results are indicative, are not a quotation and do not replace an on-site survey or system design.
03
Review policy
This guide was reviewed on 30 July 2026. Funding, tariffs, standards and regulations can change; follow the linked publisher to confirm the current position.