Divide your annual usage by ~900, then by panel wattage. A typical 3-bed using 3,500kWh wants ~4kWp — nine to ten 435W panels and about 18m² of roof.
1) Annual kWh ÷ 900 (UK yield per kWp) = target kWp. 2) Target kWp ÷ panel size (modern panels ~420–450W) = panel count. 3) Panels × ~2m² = roof area needed. Orientation adjusts step 1 — east/west roofs need ~20% more capacity for the same output.
Low-use flat/1-bed (2,000kWh): 5–6 panels. Typical 3-bed (3,500kWh): 9–10. High-use/4-bed (5,000kWh): 12–13. EV or heat-pump home (7,000kWh+): 16+ where the roof allows — and oversizing for export pays at current SEG rates.
Shading, pitch and inverter choice move real output more than one extra panel. Run the savings calculator, then let a survey finalise count.
Facts checked 21 August 2026. We link to official sources and show when facts were last verified. If a scheme changes, we update the page.
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