The short answer
Use a desktop estimate to shortlist a layout, then have the roof, structure and electrical installation assessed. The outline of a roof in an aerial image is not the same as usable installation area.
Record what the image cannot confirm
Take ground-level photographs of each roof face and note rooflights, chimneys, vents, valleys and access constraints. Do not climb onto the roof to collect them.
Ask the surveyor to identify maintenance access, the mounting arrangement and any roof work needed before installation. For a shared building, establish who can authorise the work.
Compare layouts with consistent inputs
Consider two illustrative layouts using 440 W modules. Eight modules total 3.52 kWp; ten total 4.40 kWp. Those ratings describe nominal capacity, not the annual electricity either layout will produce.
Request a generation estimate for each actual layout using the same weather dataset and loss assumptions. Do not scale one estimate by panel count if the extra panels occupy a different roof face or shaded area.
Review the timing of generation
Orientation and shading affect the pattern of output as well as its total. Consider when the home and battery can use the output, and review the estimated monthly profile.
Ask how nearby trees, chimneys and neighbouring buildings have been represented, and which uncertainties remain for the survey.
Use SolarIQ as a starting point
SolarIQ screens available roof data and explains its layout assumptions. Its 400 mm roof-edge clearance is a model setting, not a universal statement of installation compliance.
The installer must confirm the final layout and applicable requirements. A missing desktop estimate is a reason for an assessment, not proof that solar is impossible.
Before your assessment
Bring these questions with you.
- Roof photographs taken safely from ground level.
- A marked layout with obstructions and access requirements.
- Separate capacity and annual-generation figures.
- Written confirmation of any roofing work needed.