I have walked across more than a few roofs while helping homeowners plan their solar setup, and one thing never changes: every roof is different, and that difference decides how much power you actually get. This guide looks at on-Roof Solar Panels and in-roof solar panels from a fresh angle, using real numbers and plain talk instead of sales language. Whether you work with Sunsave, a local installer, or a group scheme like Switch Together, the goal stays the same — match the solar PV system to your home.
Pitch and Mounting Angle/ solar panels on flat roof
The pitch, or slope, of your roof sets the angle at which panels sit, and that angle decides how efficiently they catch sunlight. From what I have seen on site, the ideal pitch sits between 30° and 40°, which happens to match most UK homes with standard sloped roofs. Shallower pitches around 10° still work, and steeper pitches up to 60° remain usable too, just with output slightly lower than an installer’s expected yield would suggest.
A flat roof needs help from angled brackets to reach that optimal pitch, a topic covered fully in our flat roof solar panels guide. Getting the panel mounting angle between 30 and 40 degrees, and pointing panels due south, remains the gold standard, though wind loading changes everything once you go steeper. A sharper tilt angle demands more ballast, stronger frames, and secure fixings to handle increased wind loads.
Steeper inclinations raise the ballast requirement and put extra strain on the roof structure, adding additional load that a careful installer plans for through wider row separation, proper spacing between rows, and reduced shading. Interestingly, steeper mounting angles can produce less output per m2, while a shallower slope around 10 degrees sometimes delivers between 52% and 72% of more power per unit area simply because it uses roof space more efficiently.
Cost
Pricing varies more than people expect between in-roof solar panels and on-roof solar panels, mainly because of hardware, labour, and roof-specific work. A typical 4.9 kilowatt peak, or kWp, system paired with a 10kWh battery often lands around £12,000, and that figure climbs if roof tiles need replacing or a new roof goes in alongside the scaffolding. Choosing to integrate solar panels rather than mount on-roof solar panel tends to raise the bill further.
A flat roof solar system typically costs between £750 and £900 per kWp, which matters for commercial premises watching every pound. The yearly savings and extra income come from electricity displaced at around 27p per kWh; a system generating roughly 890 kWh for commercial sites can produce genuine savings, sometimes near £240 per year per kWp. Most owners see a simple payback time of 7 years to 9 years, against a system life of 25+ years — numbers I always encourage clients to check with a solar calculator before signing anything.
The Seven Factors at a Glance
Seven things decide whether a roof performs well: orientation (favour south-facing, then east, west, and finally north), shading (an unshaded roof beats partial shade, though optimised systems cope better than most people assume), and pitch (aim for 30–40°, with 10–60° still usable, and flat roofs needing brackets). Material matters too — avoid thatch and asbestos, treat glass carefully, and check general condition to confirm the structure is structurally sound.
Finally, planning rules under permitted development cover most homes, though listed buildings and conservation areas carry high impact restrictions compared with the medium impact rules elsewhere.
Shading
Orientation gets most of the attention, but shading quietly decides how much electricity a system actually produces. Solar PV systems that sit partially shaded for part of the day still work, though heavy shading hurts output badly. Most UK roofs deal with shadows from trees, chimney stacks, neighbouring properties, or dormer windows at different times of day — a chimney’s shadow at noon behaves very differently from one cast in the afternoon.
Even a quarter of roof left in shadow drags down a poorly designed system, which is why an optimised system using microinverters or power optimisers protects the output of individual panels. A shadow on one panel should never drag down the whole array. A good installer always checks this during the survey, and I would be wary of any honest installer who skips it, especially on a heavily shaded plot.
Roof Material
Your UK roof material shapes the mounting system and, in turn, the installation cost. Concrete tiles and clay tiles remain the most common UK roof type, while slate needs slate-specific hooks to protect the tiles underneath. Asphalt and composite roofing tend to be durable, and metal roofing usually accepts a lower-cost mounting system without much fuss.
Concrete flat roofs, along with felt, tar, and gravel surfaces, generally take a ballasted mounting system or an angled mounting system — both explained further in our flat roof guide. Wood shingles raise fire safety protocols to think about, and thatch brings a genuine fire risk worth discussing honestly. Asbestos roofs need a specialist, while glass roofs and conservatory roofs rarely suit a standard solar PV system, though in-roof solar panels or fully integrated solar panel systems sometimes still fit.
Roof Condition
Structural condition decides whether solar panels belong on your roof at all, and with panels expected to last 25–30 years, this is not something to guess at. A proper pre-installation survey from an accredited installer checks structural integrity, looks for damage, spots missing tiles, and flags early deterioration. Any needed repair or replacement work should happen before a solar array goes up, since fixing it afterward adds both cost and complexity.
How Many Solar Panels Can You Fit on Your Roof?
Roof size sets a hard limit on how many panels you can add, which then decides how much electricity you generate and how quickly the system pays for itself. A standard solar panel covers about 1.6 m², so even a minimum installation through a group scheme like Switch Together’s group-buying scheme often 4 panels across 6.4 m² — needs genuinely usable roof space.
A typical 4 kWp system aimed at a UK family home usually needs 10–12 panels across roughly 26 m² of clear roof space. Skylights, chimney stacks, roof vents, and dormer windows all eat into that number, so an installer always runs a proper survey first. Garage roofs, extensions, and outbuildings can add useful extra capacity too, provided they stay structurally sound and hold a workable orientation.
On-Roof vs In-Roof Solar Panels
Across the UK, most systems use panels mounted on top of an existing roof, which remains the most cost-effective approach for the widest range of roof types. In-roof solar panels, sometimes called integrated solar panels, replace the roof tiles directly, giving a cleaner appearance and a flush appearance that suits newer builds or a full roof replacement.
The trade-off sits between installation cost and looks, since roof material requirements differ between the two approaches. An installer can talk you through which route delivers the more integrated look for your budget.
What Are In-Roof Solar Panels?
In-roof solar panel, also called roof-integrated photovoltaics or RIPV, sit flush within the property’s roof rather than on top of it. They weigh less too — often between 10kg and 20kg less than traditional solar panels — though these lighter solar panels usually carry a shorter product warranty, around 15 years compared with the standard 25-year warranty. That trade-off between durability, performance, and upfront cost is worth discussing honestly before choosing between solar panels options.
How Do In-Roof Solar Panels Work?
In-roof solar panels work the same way as traditional on-roof panels underneath the surface. Daylight hits the solar cells, and through the photovoltaic effect, light particles called photons knock electrons loose within internal layers, generating electricity. The only real difference lies in installation and appearance, not in how the solar panel itself sits on the roof.
Are In-Roof Solar Panels Worth It?
Whether in-roof solar panels earn their keep depends on your situation. If you already plan to replace roof tiles, or you are buying a home and want to install solar from day one, the extra expense of a flush system makes sense despite the 5-10% efficiency decrease.
The economic benefit rarely beats on-roof solar panels on pure numbers, since initial cost savings favour the simpler option, but the aesthetic benefits matter to plenty of homeowners chasing long term savings goals. Providers like Sunsave can build a full battery system estimate around either choice.
Other Considerations for Flat Roof Solar Installations
Flat roof systems differ from sloping roof systems in one key way: rows of panels need real gaps to avoid shading each other, typically 0.5-1m, plus a clear border near the edge of the roof. Because most flat systems stay free-standing, the mounting frames and ballast rarely stress the roof structure, which matters greatly on commercial properties already carrying air conditioning systems or lift motor housing both health and safety concerns during installation and later maintenance.
Always check your roof warranties before fitting a free-standing ballasted solar system, since some roof types, particularly certain membranes like Bauder roofs, need a specialist fixing system to preserve water tightness. Roof condition matters here too; bolted panels on a tired sloping roof may need an upgrade first. Roof felt and general felt roofing face real punishment from summer heat, winter temperatures, and UV rays, which can cause leaks after roughly 10 years, while a proper roof membrane and maintenance-free membranes can last 15-20 years, sometimes stretching to 30 years.
Any new-build flat roofs should follow warm roof construction standards under Part L of the Building regulations, and providers like Spirit can help navigate planning applications where needed.
Frequently Asked Questions
Any alternatives to in-roof solar panels?
Yes solar roof tiles offer a genuinely discreet option covering the entire rooftop, though they run roughly 300% more expensive than traditional solar panel installations and involve a longer installation process, since it remains newer technology.
Can you replace roof tiles with solar panels?
You can replace standard roof tiles with in-roof solar panels built specifically as roofing materials, giving a polished appearance and seamless appearance far smoother than a bolted-on on-roof solar system. It suits anyone replacing roof tiles anyway or buying a property planning a refit, though it stays the more expensive option.
How do I know if my roof will support solar panels?
Ask an accredited installer to check whether your roof can genuinely support solar panels through a proper structural survey before any work begins.
Roof solar panel cost?
Costs vary by system size and roof type, so get a tailored roof solar panels cost quote from an installer.
In-roof solar panels vs on-roof: Both routes suit different budgets and different looks — compare in-roof solar panel against on-roof directly with your installer.