Methodology

Current status of the calculation engine

The figures currently returned by our calculators are illustrative. They are produced by a placeholder model so that the interface, the presentation of ranges and the explanation of sensitivities can be designed and reviewed before a verified engine is connected.

Illustrative output is labelled as such wherever it appears. When the verified engine goes live, each result page will state the model version and the date its inputs were last refreshed.

How we intend to source inputs

Consumption modelling starts from your own annual kilowatt hours where you provide them, and from published domestic consumption bands where you do not. Half-hourly shape is inferred from occupancy, heating type and EV charging behaviour.

Generation modelling uses regional irradiance, roof orientation and shading, with conservative performance-ratio assumptions and annual degradation applied over the modelled life.

Tariff modelling uses your own rates where you enter them. Where you do not, we use conservative national reference rates and widen the published range accordingly.

Why we publish ranges

Two identical houses with identical hardware can differ by a wide margin in annual savings, driven mostly by occupancy, tariff choice and how the system is controlled. A single-point payback figure conceals that variation.

Every result therefore shows a low and a high case, and names the specific inputs most responsible for the spread. Where our confidence is low, the range is wide, and we say why.

Review and correction

No guide on this site has yet been independently reviewed, and the author and reviewer lines currently say so. Once the editorial process is running, each guide will be written by a named author, checked by a named reviewer before publication, and carry the date it was last updated. The intended cycle is at least twice a year, and immediately when prices, grants, standards or tariffs change materially.

When we get something wrong we will correct it in place, note the correction and the date, and not quietly delete the original claim.

What this analysis is not

It is not regulated financial advice, and it does not account for your personal tax position, credit terms or finance costs unless you tell us about them.

It is not an installation specification. Sizing figures are a starting point for a conversation with an installer, and every installation requires a survey covering the electrical supply, structure, hydraulics and, where relevant, planning constraints.