Almost everything else about a solar installation can be revisited later. You can add a battery, change your export tariff, even swap the inverter. What you cannot sensibly do is move the panels. Where they go determines how much electricity you generate every day for the next twenty five years, so it deserves more thought than it usually gets, and it is worth understanding the principles before an installer proposes a layout.
Start With the Roof Slope That Faces the Right Way
In the UK, a roof slope facing south collects the most sunlight across the year. South east and south west come close behind, typically giving up only 5% or so. East or west facing slopes produce roughly 15% to 20% less than south, which is still enough for a worthwhile system, and splitting panels across both east and west slopes spreads generation usefully across morning and evening, when most households actually use electricity. We look at that arrangement properly in our guide to east west roof installations.
North facing slopes are the weak case. They produce perhaps 30% to 40% less than south in the UK and are usually only worth panelling when no other slope exists and expectations are set accordingly. If you are not certain which way your roof actually faces, and many people are a surprising 45 degrees out when they guess, you can check it in seconds with our free tool, or read our guide to working out your roof direction.
Pitch: The Angle Under the Panels
The ideal tilt for year round generation in the UK is around 35 degrees, and most British pitched roofs sit conveniently between 30 and 45, so for the majority of homes the pitch takes care of itself. Steeper roofs slightly favour winter output, shallower ones slightly favour summer. The differences within that normal range are small, a few percent, and are not worth engineering around. Flat roofs are the exception: panels there are mounted on angled frames, usually at 10 to 15 degrees, with their own spacing and ballast considerations, which we cover in our flat roof guide.
Shade Changes the Numbers More Than Direction Does
A perfectly south facing roof in the shadow of a large tree can be a worse site than a west facing roof in clear sun. Shade is the quiet deal breaker in solar design. Chimneys, dormer windows, satellite dishes, neighbouring buildings and trees all cast moving shadows through the day and the seasons, and because panels are wired in strings, shade on one panel can drag down several others.
Walk around your garden at different times of day and look at where shadows fall on the roof, remembering that the winter sun sits much lower than the summer sun. A good installer will model shading properly during the survey. Where partial shade is unavoidable, panel level optimisers or microinverters let each panel perform independently, at an added cost of a few hundred pounds that is only worth paying when shade genuinely exists.
How Many Panels Will Fit
A modern residential panel measures about two square metres, and installers need to keep a margin of roughly 30 to 40 centimetres from roof edges and the ridge. As a rough rule, a typical semi detached roof slope of 25 to 30 square metres accommodates nine to twelve panels, which at current panel sizes is a 4kW to 5kW system. Obstacles like roof windows and vent pipes claim their own space. This is another reason the layout drawing in a quote deserves scrutiny: it shows whether the installer has actually measured your roof or estimated from the street.
Beyond the Main Roof: Garages, Extensions and Gardens
Panels do not have to live on the house. A garage or single storey extension with a well oriented roof can host several panels, though the structure needs to be sound and the roof covering suitable, which a survey will confirm. Ground mounted systems in the garden are increasingly popular where space allows: they sit at the perfect angle, stay easy to clean, and avoid scaffolding entirely. In England, a single ground mounted array of up to nine square metres generally falls under permitted development, with conditions around siting; anything larger needs planning permission. The full rules are in our guide to planning permission for solar panels.
Where the Hardware Goes Inside the House
The panels are only half the layout question. The inverter prefers somewhere cool and ventilated: garages and utility rooms are ideal, lofts are common but run hot in summer, which shortens inverter life somewhat. If a battery is planned, it needs a suitable location too, ideally not a bedroom or an escape route, and current practice favours garages, utility spaces or outside walls. Think also about the cable route from roof to inverter to consumer unit, since a tidy internal run is easier to agree before installation day than during it.
Do the Desk Work Before the Doorstep Work
You can settle most of the placement question before any installer visits. Check which way your roof faces, look at the slopes with fresh eyes for shading, and form a rough view of how many panels might fit. Ten minutes of this puts you in a far stronger position to judge the layouts you are quoted. Our free tool gives you the orientation and estimated solar potential for your postcode as a starting point.
Check your roof orientation now
Use our free tool to find out which way your roof faces and whether it is suitable for solar.
Check your roof for freeCan solar panels go on a north facing roof?
They can, and in the UK they will typically produce 30% to 40% less than the same panels facing south. That changes the economics rather than eliminating them. If a north slope is genuinely the only option, a smaller system sized to your daytime usage may still be estimated to pay back, but it is essential to run the numbers with realistic output figures rather than brochure ones.
Is it better to split panels across two roof slopes?
Sometimes. An east west split produces a flatter generation curve across the day, which suits households that use electricity in the morning and evening. A single south facing array produces more in total. Splitting across slopes needs either two inverter inputs, optimisers or microinverters, which most modern equipment handles without difficulty.
Can panels be mounted on a wall instead of a roof?
Vertical wall mounting exists and a south facing wall does generate, but output is typically 25% to 30% below an optimally tilted roof array across the year, with a bias towards winter when the sun is low. It is occasionally the right answer for properties with unusable roofs, and estimates should be treated with extra caution because so much depends on the specific wall and its shading.
