Five things decide whether a roof is a good solar site: which way it faces, how steep it is, what shades it, what it is covered with, and whether the structure and the covering have twenty five years left in them. Only the last two need somebody on a ladder, and the first three can usually be settled before anybody visits.
Roof orientation for solar panels matters less than people fear
South facing is the best case in Britain and it is not the only workable one. East and west facing roofs produce meaningfully less over a year than south, but they spread generation across morning and evening rather than concentrating it at midday, which on a household that is out at lunchtime and home at six can raise the share of generation actually used. An east west split roof puts panels on both sides and flattens the curve further. North facing alone is the one orientation that is usually not worth it in the UK.
Shade is the thing that ruins a solar array
A chimney, a neighbour's conifer, a dormer or a telegraph pole can cost far more output than a poor orientation, because shading one part of a string can drag the rest down depending on how the system is wired. This is why the survey should identify shade across the day and the year, not just at the moment of the visit, and why optimisers or microinverters are a genuine answer on a partly shaded roof rather than an upsell. Winter shading is worse than summer shading because the sun is lower.
Covering and structure: what carries PV panels on roof
Concrete tile is the straightforward case. Natural slate needs care and skill because slates break and because the fixing has to be weathered properly, and a firm that is casual about slate should not be on a slate roof. Clay is similar. Fragile or old coverings and asbestos cement are separate questions about access and remaining life. Underneath all of it, the rafters and their spacing have to carry the array, and on a cut roof or an old structure that is worth a look rather than an assumption.
Remaining life: the question people skip before fitting solar panels to roof
An array is a twenty five year asset. If the covering has ten years left, the honest sequence is to re roof and install together, not to fix panels to something that has to come off. A roofer can give you the covering's remaining life in an afternoon, and it is the cheapest piece of information in the whole project. Getting it after the array is up costs a scaffold and a strip out.
Other questions people ask
Do solar panels on west facing roof slopes work?
Yes, with less annual output than south facing. The generation is shifted towards the afternoon and evening, which can suit a household that is out during the day, so the loss in output is partly offset by using more of what is produced.
What pitch is best for solar panels?
A moderate pitch in the usual British range works well and small differences matter far less than shading or orientation. On a flat roof the frame sets the angle, so the choice is a design decision instead.
Can solar panels on slate roof coverings work?
Yes, and it needs a competent roofer. Slates are brittle and the fixing has to be weathered properly, so ask specifically about experience with slate and about who makes good if a slate breaks.
How do I know if my roof is strong enough?
Have it assessed. Most ordinary domestic roofs in good condition take an array without issue, but old, altered or unusually light structures should be checked by somebody competent rather than assumed.