Start from your electricity bill, not your roof
A typical UK home uses around 2,700 to 4,100 kWh of electricity a year, and your annual figure is on your bill. In the UK climate, each kilowatt of panels facing somewhere sensible generates roughly 850 to 1,000 kWh a year. Divide your usage by that and you have the system size that would notionally cover it: a 3,400 kWh household points at around a 4kW system.
At today's panel sizes of around 430W each, 4kW is ten or eleven panels, needing roughly 20 square metres of roof. A two bed terrace often takes 6 to 8 panels, a three bed semi 10 to 12, and a detached house with a big roof can go to 14 or more if the usage justifies it.
What your roof changes
South-facing at a 30 to 40 degree pitch is the textbook best, but an east-west roof loses only around 15% across the year and spreads generation into morning and evening, when you are actually home to use it. North-facing pitches are usually left alone. Shading matters more than orientation: a chimney or tree that shades panels for part of the day drags the whole string down unless the design accounts for it with optimisers.
Flat roofs take panels on tilted frames, angled and spaced so rows do not shade each other, which uses more area per panel. All of this is what the survey establishes, and it is why a quote given without anyone seeing your roof, even on satellite imagery, deserves caution.
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Compare solar quotesWhy bigger is not automatically better
Panels you cannot use export to the grid at a rate well below what you pay to import, so a system dramatically bigger than your usage has a longer payback per panel. The exceptions that justify going larger: a battery to soak up the surplus, an EV arriving on the driveway, or a heat pump in the plan, each of which turns excess generation into avoided import.
Whether a battery is worth adding is its own calculation, covered in is battery storage worth it. For the system itself, a 4kW installation runs to about £8,400 fitted, and you can compare solar quotes from MCS-certified installers sized to your actual usage rather than a standard package.
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Up to three trusted, MCS-certified installers quote for the work. Free, no obligation.
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