Roof suitability and shading
How roof orientation, pitch, shade, roof condition and layout affect solar generation and payback.
Key takeaways
- Annual generation depends on roof direction, pitch, shading, location and system design.
- PVGIS can help sense-check annual kWh estimates.
- Roof repairs are best sorted before panels go up.
What makes a strong solar roof
A strong solar roof has enough usable space, limited shading, a sensible pitch and a direction that catches useful daylight. South-facing roofs often produce the highest annual output, but east-west roofs can still be useful because they spread generation across the day.
The right layout depends on your household too. If you use more power in the morning and late afternoon, an east-west split can sometimes fit your demand better than a single midday peak.
Shade is expensive
Shade from trees, chimneys, dormers, aerials or nearby buildings can reduce output. It can also make one part of an array perform worse than another. That doesn't automatically rule out solar, but it means the design needs to be honest.
Ask the installer how shade has been modelled. If the estimate assumes a clean roof and you can see shade across the proposed array, challenge it.
Use PVGIS as a sense check
PVGIS from the European Commission gives location-based solar radiation and PV performance estimates. It won't know every detail of your roof unless you enter good inputs, but it's a useful independent check against a quote.
If an installer's annual kWh estimate is far above a sensible PVGIS case, ask why. Sometimes there's a good reason. Sometimes the quote is just too optimistic.
Roof condition and access
Panels are long-life equipment, so don't ignore the roof under them. If tiles, felt, battens or flat-roof coverings are near the end of life, sort that before installation if you can.
Scaffolding and access also affect cost. A cheap panel price can be swallowed by a tricky roof, awkward cable route or extra electrical work.
Sources checked
- Energy Saving Trust solar panel guideConsumer guidance on costs, payback, savings and maintenance.
- European Commission PVGISSolar radiation and PV performance estimates by location.