Solar Panel System Size Guide (UK)
How many panels do you need? A practical guide by house type, usage, and roof conditions.
System Size by House Type
Based on average UK electricity consumption and standard 400–420W panels (2026). These are starting points — actual sizing depends on your specific usage and roof.
1-Bed Flat
2-Bed Terrace
3-Bed Semi-Detached
4-Bed Detached
Assumes 400–420W monocrystalline panels. Standard panel wattage in 2025–2026. Sources: Which?, Energy Saving Trust, MCS.
How Roof Direction Affects Panel Numbers
| Roof Direction | Relative Output | Adjustment |
|---|---|---|
| South-facing | 100% (optimal) | Baseline — no extra panels needed |
| East or West | ~85% of south | Add 1–2 extra panels |
| North-facing | ~70% of south | Add 2–3 extra panels |
Roof Pitch
30–40° is ideal (matches most UK roofs). Shallower or steeper pitches reduce efficiency by 10–20% — adjust system size up by 10–25%.
Shading
Less than 20% shading is best. Over 80% shading cuts output by 50% — may need double the panels or microinverters/optimisers.
How to Calculate Your System Size
Step 1: Find your annual usage
Check your electricity bills. Average UK household: 2,700–4,200 kWh/year.
Step 2: Estimate local yield
Each kWp generates 900–1,000 kWh/year in the UK. Southern England: ~1,000+. Northern areas: 800–900.
Step 3: Apply the formula
System size (kWp) = Annual kWh needed ÷ Local yield (kWh/kWp)
Example: 4,000 kWh/year in south-east (950 kWh/kWp) → 4.2 kWp (10–11 × 400W panels)
Step 4: Factor in losses
Add 20–30% for inverter efficiency, dirt, and degradation over time.
Get a Properly Sized Solar Quote
An MCS-accredited surveyor will assess your roof and usage for a precise system design.
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