Most people researching solar panels focus first on how many panels they’ll need and what it will cost. But one factor that gets less attention, and can make a real difference to how much electricity a system actually generates, is which way your roof faces.
South-facing roofs (the ideal). In the UK, a roof facing due south receives the most consistent sunlight throughout the day, which means panels mounted there generate the most electricity for a given system size. This is why installers often quote their best-case savings figures based on a south-facing example, even though plenty of homes don’t have that exact orientation.
East and west-facing roofs. These aren’t far behind. A roof facing east or west typically loses somewhere around 10-15% of the output you’d get from a due-south roof, since the panels catch strong sun for only part of the day rather than the full arc. For many households, this difference is small enough that installing on an east or west roof is still very worthwhile, particularly if it’s the only usable space available.
North-facing roofs. This is where output drops off more significantly, sometimes by 30% or more compared to south-facing, since the roof receives mostly indirect light. Panels can still be installed here, but the economics are weaker, and it’s worth discussing with an installer whether a different roof section, or a mix of orientations, makes more sense for your property.
Splitting a system across two roof faces. Many homes don’t have one large south-facing roof plane, but instead have east and west sections, such as a semi-detached property with panels split across the front and back. Splitting a system this way can actually be a smart choice, since it captures sunlight earlier in the morning and later in the afternoon, spreading generation more evenly across the day rather than concentrating it all around midday when a household may not even be home to use it.
Shading matters as much as direction. Even a perfectly south-facing roof can underperform if it’s regularly shaded by a chimney, a neighbouring tree, or a taller building nearby. A proper site survey will usually flag this, and it’s one of the reasons online calculators based on postcode alone can only ever give a rough estimate rather than an exact figure for your specific property.
Why this matters when sizing a system. Roof direction affects how many panels you’ll actually need to hit a given output target, since a less favourably angled roof needs more panels, or panels with a higher wattage rating, to produce the same amount of electricity as a smaller system on an ideal south-facing roof. If you’re trying to work out roughly how many panels your home might need, there’s a straightforward guide that walks through the maths based on average household usage, from GSM’s solar panel installation guide, a useful starting point before getting a proper site assessment done.
Roof direction isn’t something you can change, but understanding how it affects your system means you can go into conversations with installers already knowing what questions to ask and why two similar-looking quotes might differ.
