What the figures are, and what they are not

Estimates, not guarantees

Generation, savings, payback and every other result are estimates. They are not a guarantee of performance, of savings or of a financial return, and should not be read as one. A system's real output will be different from year to year.

What the yield depends on

The predicted energy is only as good as what it is built on:

• Weather data — measured or modelled sunshine and temperature for the site. Real years are sunnier or cloudier than the record.
• Losses — soiling, shading, wiring, temperature, inverter efficiency, degradation and availability, each set as an assumption.
• Inputs — the roof, orientation, equipment data, consumption and tariff entered for the project. Wrong inputs give a confident answer that is wrong.

Because of this, designs show the uncertainty in the yield as well as the central figure: a P50 value, which the yield is expected to exceed in half of all years, and a P90 value, which it is expected to exceed in nine years out of ten. The open estimator is simpler still and says so on the page.

Every number comes from the calculation engine

The figures are calculated by a rule-based engineering engine, the same way every time. AI is used only to read documents, draft wording and give a second opinion. It never produces a figure, and it is not allowed to change one. See how the tool uses AI.

Preliminary until an engineer approves it

A design is preliminary until a qualified engineer has reviewed and approved it in the tool, and a proposal can only be issued from an approved design. Even then it is a design for quotation. The final construction design, including the structural and electrical checks, is prepared and signed off by a qualified engineer before anything is ordered or installed.

What still applies

An approved design does not replace any of these:

• Local codes and standards for electrical installations, structures and fire safety where the system is built.
• Utility approval — connection, export limits, protection settings and metering are set by the network operator, and the tool does not encode country-specific rules.
• A site survey to confirm the roof, its structure, shading, cable routes and the existing electrical installation.

Known limits of the model

Shading is entered from a survey rather than modelled in three dimensions, the structural check is a load sanity check only, and cable ratings are reference values for one installation method. The full list of assumptions is printed in every design report.

These points form part of the Terms of Use. Questions go to [email protected].