An in roof array replaces a patch of tile or slate rather than sitting on top of it, so the panels become the weathering layer for that part of the roof. It looks considerably better and it introduces a detail that an on roof system does not have, which is a junction between a manufactured tray and a traditional covering that has to shed water for twenty five years.
In roof against on roof solar panels: how the two systems differ
An on roof array stands on brackets fixed through the covering into the rafters, with the tiles doing the weathering as they always did. An in roof array removes the covering over its footprint and sits in a proprietary tray or flashing kit that carries water around and under the panels to the covering below. The visual difference is obvious from the ground. The construction difference is that the array is now part of the roof, so the flashing detail, the ventilation behind the panels and the junction with the surrounding tiles are what keep the house dry.
What integrated PV panels cost and why
In roof usually costs more than on roof for the same generation. The tray or flashing kit is an extra material, removing and setting aside the covering is labour, and the detailing takes longer and needs somebody who understands roofs rather than only arrays. On a new build or a re roof the gap narrows sharply, because the covering is coming off anyway and there is less tile to buy. That sequencing is the single biggest lever on the price, which is why in roof is a natural choice when the roof is being replaced and an expensive one when it is not.
Solar panel tiles and a solar slate roof are a different product again
Solar tiles, solar slates and solar shingles replace individual units of covering rather than a whole panel sized area. They are the most discreet option and the most expensive per unit of generation, they use many more electrical connections, and the product range in the UK is narrower. They earn their place on a listed building, in a conservation area or where a planning officer has views, and they are hard to justify on cost alone elsewhere.
What to ask local solar roof installers before choosing in roof
Who is detailing the junction with the surrounding covering, and are they a roofer. Whether the panels are ventilated behind, because an in roof array runs hotter than one with air moving under it and heat costs output. What the roof covering's remaining life is, since taking an in roof array out later is a bigger job than lifting an on roof one. And who carries the leak risk in writing, because the array and the roof are now the same thing.
Questions people ask about in roof solar panels
Are in roof solar panels less efficient?
They can run slightly warmer than an on roof array because there is less air movement behind them, and warmer panels produce a little less. A well ventilated in roof system narrows the gap. It is a real effect and usually a small one compared with orientation and shading.
Can in roof panels be retrofitted?
Yes, but it means stripping the covering over the array's footprint and fitting the tray, which is why retrofitting costs more than an on roof system. The natural moment is during a re roof or on a new build.
Do inset solar panels leak more often?
Not inherently, but the risk sits in the detailing rather than in the panels, so the competence of whoever does the flashing matters more than with an on roof array. Ask who details it and get the leak responsibility in writing.
Are solar tiles worth the extra?
On appearance and planning grounds they can be, particularly on a listed or protected building. On generation per pound they are not, so the decision is usually aesthetic or regulatory rather than financial.