How many solar panels do I need?
Start from how much electricity you actually use. We convert that into a system size, a panel count and the roof space it needs — adjusted for which way your roof faces and how much shade it gets.
Figures checked October 2026 Estimate
Based on an estimated UK yield of ~850kWh per kWp per year for a well-sited system, and modern 430W panels. Real yield varies by region — Scotland and northern England get a little less, the south coast a little more.
The maths behind “how many panels”
The calculation most installers use is simple: divide your annual electricity use by the expected yield per kilowatt of panels. In the UK that yield is an estimated 850kWh per kWp per year for a decent south-facing roof — so a home using 2,900kWh needs around 3.4kWp to generate the same amount across the year. With modern panels rated at 430W, that’s about 8 panels. Each panel is roughly 2m², so you need around 16m² of usable roof — most semi-detached and detached houses have that on one slope; many terraces do too.
Two adjustments matter. Direction: an east- or west-facing roof still produces around 80% of a south-facing one, and actually matches morning/evening demand better; a north-facing roof drops to roughly 60% and rarely justifies itself. Shading: even partial shading from a chimney or tree can cut output noticeably, because shaded cells drag down a whole string of panels — that’s why we derate shaded roofs and why optimisers exist.
Should you cover 100% of your usage?
Not necessarily. Solar generates most in summer, when you use least, so a system sized at 100% of annual use still exports a lot in June and imports on December evenings. Many households find a system covering 70–90% of annual use the sweet spot, especially without a battery. If you’re adding a battery, an electric vehicle or a heat pump later, sizing up now is cheaper than extending later — panels are the cheapest part of the install. Run your result through the cost calculator and payback calculator to see the full picture.
Panel count questions
How many panels for a 3-bed house?
For a typical 3-bed home using ~2,900kWh a year: an estimated 8–10 panels (3.5–4.3kWp) on an unshaded south-facing roof. East/west roofs need one or two more panels for the same generation.
How much roof space does that take?
About 2m² per panel including gaps, so roughly 16–20m² for a typical system. Installers also need margins from the ridge, eaves and edges, which is why a survey matters more than a tape-measure guess.
My bill is monthly over winter — is the conversion reliable?
It’s a rough estimate. Winter bills are higher than summer ones, so multiply an average month, not your January bill. Your annual statement or smart meter app gives the real kWh figure, which is always the better input.
Ready for real prices?
Calculators give you the ballpark. Get free, no-obligation quotes from MCS-certified UK installers and compare them against these numbers.