People ask about mounting solar on a dormer because it is the flat surface they can see from the garden. It is usually the worst surface on the house for the purpose: small, often shaded by the main roof above it, and waterproofed with a membrane that nobody wants to make holes in. It is not impossible, and it is rarely the right answer.
The three problems with a dormer top
It is small, so the array is a handful of panels at best and the fixed costs of an installation are spread over very little generation. It frequently sits below the main ridge on the same elevation, so the main roof shades it for part of the day, and shading on one module can drag down a whole string unless the electronics are chosen for it. And it is a flat roof, so anything fixed to it either penetrates the waterproofing or has to be ballasted, and a dormer roof was not designed for ballast.
If it is done anyway
A flat roof array needs a mounting system designed for flat roofs, either penetrating with properly weathered upstands or non penetrating with ballast, and the structural capacity has to be confirmed rather than assumed because dormer roofs are light structures. Panels tilted up on frames catch wind, and wind uplift on a small high roof is significant. Where the membrane is under warranty, check whether the fixing method voids it before anyone drills.
Where the panels usually go instead
On a house with rear dormers the main roof slopes either side of the dormer are normally the right home for an array, and a hipped or gable slope with a reasonable orientation will out generate a dormer top many times over. An installer worth using will measure the available slopes, model the shading including the dormer itself, and tell you the dormer is not worth it if that is the answer.
Who should be doing the work
Certification under a recognised scheme matters here because it governs both the quality expectation and access to export arrangements, and the standards cover the structural survey as part of the installation. A roof penetration on a dormer is also roofing work, so it is reasonable to ask who is making the waterproofing good and what happens if it leaks afterwards.
Questions people ask about solar panels on dormer roof
Can solar panels go on a flat dormer roof?
Physically yes, with a flat roof mounting system and a structural check. Whether it is worth doing is a different question, and on most houses the main roof slopes are a far better use of the same money.
Will fixing panels to a dormer cause leaks?
It can if the penetrations are not properly weathered into the membrane, and it may affect an existing waterproofing warranty. A non penetrating ballasted system avoids the holes but adds weight a light dormer roof may not have been designed for.
Does the dormer shade the rest of my array?
It can, depending on its height and the sun path. A competent installer models the shading across the day and the year and positions the array and the electronics around it rather than ignoring it.