How Many Solar Panels Do I Need?
A simple UK sizing guide by property type, energy use and EV — written by working MCS-registered electrical contractors in Devon.
The 1kW per 1,000 kWh rule
As a fast estimate: every 1kW of solar on a south-facing UK roof produces around 900–1,000 kWh per year. Match that to your annual usage on your last electricity bill.
Sizing by property
| Home | Typical use | System size | Panels (405W) |
|---|---|---|---|
| 1-bed flat | 1,800 kWh | 2 kW | 5 |
| 2-bed | 2,500 kWh | 3 kW | 7–8 |
| 3-bed | 3,200 kWh | 4 kW | 10 |
| 4-bed | 4,200 kWh | 5–6 kW | 12–15 |
| 5-bed / large | 5,500 kWh+ | 7–8 kW | 17–20 |
| + Heat pump | + 3,000 kWh | + 3 kW | + 7–8 |
| + EV (8k miles) | + 2,000 kWh | + 2 kW | + 5 |
Things that change the answer
- Roof orientation — east/west splits need ~20% more panels than due-south
- Shading — chimneys, trees and dormers reduce yield significantly
- Pitch — 30°–40° is best in Devon; flat roofs need ballast frames
- Battery — without storage you only use 25–35% of generation directly
- Smart Export Guarantee tariff — Octopus Outgoing pays for what you export
- EV charger — surplus diversion to a Zappi, Hypervolt or Ohme adds value
Want a proper sizing — not a guess?
Free in-person survey across Devon. We measure the roof, model your usage and quote fixed-price.
Frequently Asked Questions
How many solar panels do I need for a 3-bed house?
A typical UK 3-bed home uses 2,700–3,500 kWh of electricity per year and needs a 4kW system — that's 10 modern 405W panels. South-facing roofs in Devon need fewer panels than east/west splits.
How many solar panels do I need to run a house off-grid?
A fully off-grid Devon home typically needs 8–12kW of solar (20–28 panels) plus 15–25kWh of battery storage and a back-up generator for winter. Most homes go partial off-grid with grid as backup — far more cost-effective.
How many panels do I need for an EV?
A typical EV doing 8,000 miles/year uses about 2,000 kWh — so add 2kW (5 panels) on top of your household calculation. Pair with a solar-aware EV charger like Zappi, Hypervolt or Ohme to charge directly from surplus.
How much roof space do solar panels need?
A 405W panel measures roughly 1.7m × 1.1m (1.9m²). A 4kW (10-panel) array needs about 19m² of unshaded roof. South, south-east or south-west pitches between 15° and 50° are ideal in Devon.