Search for the best angle for solar panels and you will find a rule of thumb repeated everywhere: tilt them at an angle equal to your latitude. In the UK that would mean somewhere between 50 degrees on the south coast and 58 in the north of Scotland. It sounds scientific. For British homes it is also wrong, and by more than you might expect.
The Answer: About 40 Degrees, Almost Everywhere
We ran PVGIS, the European Commission's free solar model, for six UK cities. It uses around twenty years of satellite weather data, so it knows how often the sky over each place is actually clear. Here is the tilt it finds produces the most electricity over a whole year for a south facing panel, along with the estimated yearly output per kilowatt of panels after normal system losses:
- Plymouth: 39 degrees, about 1,120kWh per kW.
- London: 40 degrees, about 1,025kWh per kW.
- Birmingham: 40 degrees, about 970kWh per kW.
- Manchester: 39 degrees, about 890kWh per kW.
- Edinburgh: 42 degrees, about 910kWh per kW.
- Inverness: 41 degrees, about 815kWh per kW.
Two things stand out. The ideal angle hardly moves, three degrees across the length of Britain. And in this model Edinburgh slightly out-generates Manchester, which will not surprise anyone who has spent a wet week in Manchester.
Why the Latitude Rule Gets the UK Wrong
The latitude rule assumes most of your energy arrives as a direct beam from a clear sky, so you should aim the panel squarely at the sun. That holds in Arizona. It does not hold here. Around half of the solar energy reaching the UK arrives as diffuse light, scattered through cloud from the whole of the sky rather than from the sun's disc.
A flatter panel sees more of that bright grey dome overhead. A steeper one sees more of the ground and the house opposite. So in a cloudy climate the best angle drops well below your latitude, and the further north you go, the more the extra cloud offsets the lower sun. That is why Inverness, nearly 800 kilometres north of Plymouth, wants only two degrees more tilt.
How Much Does a Different Angle Cost You?
This is the part that matters, because you cannot easily change your roof. The good news is that the curve is remarkably flat around the top. For a south facing roof, compared with the ideal angle in the same city:
- 30 to 50 degrees: within 1 to 2% of the best figure.
- 25 degrees: about 97 to 98%.
- 20 degrees: about 94 to 96%.
- 15 degrees: about 92 to 94%.
- 10 degrees: about 89 to 91%.
- Completely flat: about 80 to 84%.
- 60 degrees: about 95 to 97%.
- Vertical, such as a south facing wall: about 71 to 75%.
Most pitched roofs in Britain sit somewhere between 30 and 45 degrees, which puts them inside that top band. If your roof is in that range, the angle question is answered, and you can spend your attention on the things that matter more: direction, shading and what you are quoted.
Steep Roofs Win in Winter, Shallow Roofs Win in Summer
The yearly totals hide a seasonal trade. A steep panel faces the low winter sun more squarely. A shallow one faces the high summer sun. For a 4kW south facing system in Birmingham, comparing a 20 degree roof with a 50 degree one:
- December: the 50 degree roof makes about 50% more.
- November to February combined: about 735kWh against 535kWh.
- June: the 20 degree roof makes about 13% more.
- Across the whole year: the steeper roof comes out roughly 4% ahead.
One result we did not expect: a vertical south facing wall produces more in December and January than a 20 degree roof does, because it faces the low midwinter sun almost head on. It loses badly in summer, so its yearly total is lower, but it is a useful fact if most of your demand is in winter.
Does this mean you should prefer a steep roof? Usually not deliberately. Winter generation is small whatever the angle, as our guide to how solar panels perform in winter explains, and a few extra kilowatt hours in January will not change the economics. But it does explain why two neighbours with identical systems can see quite different winter figures.
East and West Roofs Prefer a Shallow Pitch
Everything above assumes the roof faces south. Turn it east or west and the logic flips: the steeper the roof, the more it leans away from the sun for half the day. In London an east facing roof at 15 degrees produces about 83% of the best south figure, but at 45 degrees it drops to about 77%. If you have an east and west roof, a shallow pitch is genuinely helpful. More on that in our east and west facing roof guide.
Flat Roofs: Why Installers Use 10 to 15 Degrees
If panels can be tilted to any angle, why not set them at 40 degrees on a flat roof? Because a steep panel casts a long shadow, so rows have to be spread far apart, and it catches the wind like a sail, which means heavier ballast or fixings. A tilt of 10 to 15 degrees gets around 89 to 94% of the ideal output, lets far more panels fit on the same roof, and keeps the frames low. On a small flat roof, more panels at a modest angle nearly always beats fewer panels at the perfect one. Our guide to solar panels on flat roofs goes into the detail.
How to Find Your Roof Pitch
You do not need a ladder. The easiest method is in the loft: rest your phone along a rafter and use a spirit level or inclinometer app, many of which are free and some of which come built into the phone. If you cannot get into the loft, stand square on to the gable end of the house, take a photograph, and measure the angle of the roof line on screen with a protractor app. Plans from when the house was built or extended will often state the pitch too.
If all of that sounds like too much effort, it is worth remembering the conclusion above: for a south facing roof between 30 and 50 degrees, the answer will not change anything.
What About the Best Angle for My Postcode?
People often search for the best panel angle by postcode, expecting a different answer for Cornwall and Caithness. As the figures above show, the ideal tilt varies by only a few degrees across the whole of Britain. What changes from one address to the next is not the ideal angle but your actual roof: which way it faces, how steep it is, and what shades it. Enter your postcode in our free tool to see your roof direction on a satellite map and an estimate of what panels there could generate.
See what your own roof could generate
Our free tool reads your roof from aerial data and gives an estimated yearly output that already allows for its direction and slope.
Check your roof for freeWhat is the best angle for solar panels in Scotland?
Slightly steeper than in southern England, but only just. Our figures put the ideal at about 42 degrees for Edinburgh and 41 for Inverness, against 39 to 40 for Plymouth and London. Anything between 30 and 50 degrees gets within a couple of per cent of the best figure in either country.
Is 45 degrees too steep for solar panels?
No. A south facing roof at 45 degrees produces essentially the same yearly total as one at 40, and a little more in winter. Very steep roofs of 60 degrees still get about 95% of the best figure. Steepness only becomes a real problem on roofs facing east, west or north.
What angle should solar panels be in winter?
For winter output alone, steeper is better: around 60 degrees or more faces the low midwinter sun most squarely. But home panels are fixed at one angle for the whole year, and since winter generation is small whatever you do, it makes sense to choose the angle that maximises the yearly total rather than the winter figure.
Does a flat roof need panels at 30 to 40 degrees?
No. Most flat roof installations use 10 to 15 degree frames, which give around 89 to 94% of the ideal output while letting more panels fit and keeping wind loading down. Panels laid completely flat lose more, around 16 to 20%, and also collect dirt because rain does not run off.
