Solar Panels on a North Facing Roof: The Honest UK Numbers

Look along any British street from above and you will spot a pattern. The panels sit on one side of the roofs and the moss grows on the other. That is not a coincidence. The north facing slope is the one that stays damp and shaded, and it is the one installers quietly steer people away from.

But steering away is not the same as ruling out. If the only roof you have faces north, you deserve a straight answer about what it would produce, rather than a polite "not really suitable". So we ran the numbers.

The Short Answer

On a typical UK roof pitch of around 35 degrees, north facing panels produce roughly 52 to 56% of what the same panels would make facing south at the best angle. On a shallow north roof of 15 degrees or less, that figure climbs to around 70%. On a steep north roof of 45 degrees or more, it falls below half.

So a north roof is not useless. It is a roof that does the same job for roughly half the reward, and whether that is worth paying for depends almost entirely on how steep it is.

Where These Figures Come From

We used PVGIS, the free solar model published by the European Commission, which combines nearly two decades of satellite weather records with the geometry of a roof. We ran it for Plymouth, London, Birmingham, Manchester, Edinburgh and Inverness, at every common pitch and every compass direction, with standard allowances for wiring and inverter losses. The percentages below compare each roof with a south facing roof at the ideal angle in the same city.

• North facing at 10 degrees: about 72 to 76%.
• North facing at 15 degrees: about 68 to 72%.
• North facing at 25 degrees: about 60 to 64%.
• North facing at 35 degrees: about 52 to 56%.
• North facing at 45 degrees: about 43 to 48%.
• North east or north west at 30 degrees: about 63 to 67%.

What surprised us was how little the city mattered. A north roof in Plymouth and a north roof in Inverness lose almost exactly the same share of their potential. The pitch, on the other hand, matters enormously.

Why the Pitch Changes Everything

Picture a sheet of card lying flat on a table in the garden. It catches light from wherever the sun happens to be. Now tilt it so it leans away from the sun. The steeper you tilt it, the more it turns its back on the light. A north facing roof is exactly that: a surface leaning away from the sun, and the steeper it leans, the less it sees.

A shallow north roof, on the other hand, is not far off flat, and flat panels in the UK still collect over 80% of the best possible figure. That is why a low pitched north facing extension, garage or bungalow roof can be a perfectly reasonable place for panels, while the steep north slope of a Victorian terrace usually is not.

Summer Is Fine. Winter Is Where It Falls Apart.

Here is the part most quotes leave out. A north roof does not lose a steady half of its output all year. It loses very little in summer and almost everything in winter.

In June the sun rises in the north east, climbs high overhead and sets in the north west, so for the first and last few hours of a long day it is actually shining on the north side of your house. For a 35 degree north roof in Birmingham, June output comes to about 82% of a south roof. In December, when the sun barely clears the rooftops across the road and stays in the southern sky all day, the same roof manages about 20%.

• June: about 82% of a south roof at 35 degrees, and about 97% at 15 degrees.
• April and August: about 52 to 64% at 35 degrees.
• October and March: about a third at 35 degrees.
• November to January: about a fifth to a quarter, whatever the pitch.

That pattern matters because summer is when you are least likely to use the electricity yourself. Long evenings, no heating, people away on holiday. A north roof produces most of its energy in exactly the months when a larger share of it gets exported for a modest payment rather than used in the house at full price.

What That Does to the Money

Take a 4kW system that would generate about 3,400kWh a year on a good south facing roof. Put the same panels on a north roof and you get roughly:

• At 35 degrees: about 1,800kWh a year.
• At 15 degrees: about 2,400kWh a year.

The cost, though, does not shrink with the output. Scaffolding, panels, inverter, wiring and labour come to much the same figure whichever slope they go on, typically £5,500 to £8,000 for 4kW. Using the same assumptions as our tool (electricity used at home valued at the current price cap rate, surplus exported at 12p), a south roof like this saves an estimated £600 or so a year and pays back in roughly 9 to 13 years. The 35 degree north roof saves an estimated £340 a year and takes somewhere around 16 to 24 years. The 15 degree north roof sits in between at about 12 to 18 years.

Panels are usually warranted to keep producing for 25 years or more, so even the slow case does eventually come out ahead. But a 20 year payback leaves very little room for the things that go wrong in real life, such as an inverter that needs replacing, a roof repair that means taking the panels off, or a house move. These are estimates, and your own figures will depend on your usage, your tariff and what you are quoted, but the gap between the two roofs is real.

North East and North West Are a Different Conversation

A roof that faces north east or north west is not a north roof with a slightly different label. It catches the early morning or the evening sun properly for half the year, and at 30 degrees it produces around 63 to 67% of the best figure, which is closer to a west facing roof than to a due north one. If your compass says your back roof faces somewhere around 300 or 60 degrees, it is worth a proper quote rather than an automatic no.

Better Options When Your Best Roof Faces North

Before deciding on the north slope, it is worth checking whether there is a better surface you have overlooked.

• The other slopes. Hipped roofs have four sides, and on a house whose front and back face north and south, the side slopes face east and west. An east and west split often beats a single north array comfortably.
• A flat roof on an extension, garage or dormer. Panels can be tilted towards the south on frames, which turns a north facing house into a south facing installation. Our flat roof guide covers how this works.
• The garden. A ground mounted array or a small frame on a south facing wall or fence avoids the roof question entirely, subject to planning limits.
• Plug-in solar. If the problem is cost rather than space, an 800W plug-in kit on a south facing balcony, wall or patio is now legal in Great Britain and costs a fraction of a roof system.

Our guide to solar panels on flat roofs explains the frame option, and our article on plug-in solar versus rooftop solar sets out where a small kit makes more sense than a full installation.

When a North Roof Can Still Make Sense

There are situations where we would still look seriously at it. If the pitch is shallow, under about 20 degrees. If you are re-roofing anyway, so the scaffolding is already paid for. If someone is at home through the day in summer, running a heat pump for hot water or charging an electric car, so more of that summer output gets used rather than exported. Or if you plan to stay in the house for a long time and simply want to make some of your own electricity, accepting that it will take a while to pay for itself.

Any MCS certified installer has to give you a written performance estimate that reflects your roof direction, pitch and shading. If an installer quotes a north roof without one, or with a figure that looks like it belongs to a south roof, go elsewhere.

Many people who think their roof faces north are actually looking at a slope that faces north east or north west, which is a much better proposition. Check your roof direction with our free tool before you write it off, and if you want the wider picture, our guide to whether a roof needs to face south covers every direction.