South East or South West: Which Roof Is Better for Solar Panels?

Very few British roofs face exactly south. Streets were laid out to suit roads, rivers and the shape of a field, not the sun, so most homes with a good roof have one that faces somewhere between south east and south west. If yours is one of them, you may have wondered whether the side of south you landed on matters. It does, a little, but probably not in the way you think.

Over a Year, It Is Close to a Tie

We modelled both directions in PVGIS, the European Commission's solar model, for six UK cities at a typical 35 degree pitch. Compared with the best possible south facing roof in the same city, a south east roof produced about 93 to 95% and a south west roof about 93 to 94%.

In Plymouth, Edinburgh and Inverness the two came out level. In London, Birmingham and Manchester the south east roof was a point or two ahead. That runs against what many people assume, and the likely reason is the British weather. Cloud tends to build through the day, so afternoons are a little greyer on average than mornings, and panels also run slightly more efficiently in the cooler morning air.

Either way, the difference is small enough to ignore. On a 4kW system in Birmingham, our model put the yearly totals at about 3,670kWh for south east and 3,620kWh for south west. That is a gap of about 50kWh, worth perhaps £5 to £10 a year.

The Real Difference Is the Clock

Where the two roofs differ sharply is in when the electricity turns up. We ran the hourly figures for 2019 to 2023 in Birmingham and split each roof's output by time of day, on UK clock time:

• Before 11am: about a third of a south east roof's output, against about 14% for south west.
• Between 4pm and 7pm: about 9% of a south east roof's output, against about 21% for south west.
• For comparison, a due south roof makes about 23% of its energy before 11am and about 15% between 4pm and 7pm.

In plain numbers, a 4kW south west system produces something like 775kWh a year in the 4pm to 7pm window, while a south east one produces around 330kWh. A south east roof front loads the day. A south west roof keeps going into the early evening, and in high summer, when the sun sets in the north west after 9pm, it is still generating usefully after most people get home from work.

Why Timing Is Worth Money

Electricity you use in the house as it is generated saves you the full price of a unit, currently around 25p. Electricity you do not use is exported, and on a good export tariff earns around 12p. So every kilowatt hour that lands while you are home and running something is worth roughly twice as much as one that goes back to the grid.

For a household that is out from eight until five and does its cooking, washing and television in the evening, a south west roof lines up better with real life. For a household with someone working from home, or one that runs the dishwasher and washing machine in the morning, a south east roof does the same job.

How much is that worth? Less than the hourly figures suggest, because a lot of daytime electricity goes on things that run regardless, like the fridge. For a typical household that is out during the day, a south west roof might let you use an extra 150 to 250kWh a year yourself rather than exporting it, which is roughly £20 to £30 a year. Useful, but not a reason to choose one house over another.

Shade Matters More Than the Compass

If there is one thing that should decide between two roughly southern slopes, it is shade. A tall tree, a chimney stack or a neighbour's extension to the west will take a bite out of a south west roof's best hours, while the same obstacle to the east will barely touch it. Stand in the garden on a sunny afternoon in late spring and look at where the shadows fall. That ten minute check will tell you more than any compass reading.

What About Export Tariffs That Pay More in the Evening?

Some suppliers offer export tariffs with a higher rate between 4pm and 7pm, when the grid is under most strain. At first glance that seems to favour a south west roof. In practice these tariffs are generally designed for, and limited to, homes with a battery, and once you have a battery you can choose when to export regardless of which way the panels face. Rates and eligibility change often, so check the current terms with the supplier before you factor them in.

If You Have Both

Plenty of homes, particularly those with hipped roofs or L shaped extensions, have both a south east and a south west slope. Using both is perfectly sensible: you get a longer, flatter generation curve across the day, which suits most households well. The installer will need an inverter that can handle two separate strings of panels, which most modern units do. Our guide to east and west facing roofs covers split arrays in more detail.

The Verdict

A south east roof and a south west roof are both very good homes for solar panels, within a few per cent of a due south roof and of each other. South west suits people who are out all day. South east suits people who are home in the mornings, and in much of the country it generates fractionally more. A battery evens the two out, and shade beats both considerations. If you are not sure which side of south your roof sits, check your roof direction with our free tool, which gives the bearing in degrees. For how the other directions compare, see our guide to whether a roof needs to face south.