Quick answer: how many panels?
For a typical UK 3-bedroom home using ~3,400 kWh/year, you need 10–12 solar panels (a 4 kW system) using standard 400W panels. That covers most of your annual electricity usage in southern England. In Scotland, where sun hours are lower, you may need 12–14 panels for the same coverage.
The exact number depends on four things: your annual electricity usage, your region's sun hours, the wattage of the panels you choose, and your roof direction. Below is a practical breakdown for every common scenario.
Panel count by house size
Most people think in terms of house size rather than kWh usage. Here's the translation — but remember, your actual electricity bill matters more than your bedroom count.
| House type | Typical usage (kWh/yr) | System size | Panel count (400W) | Annual generation |
|---|---|---|---|---|
| 1-bed flat / small house | 1,800–2,500 | 2–3 kW | 5–8 | 1,700–2,550 kWh |
| 2-bed terrace | 2,500–3,200 | 3 kW | 7–8 | 2,550 kWh |
| 3-bed semi (most common) | 3,200–3,800 | 4 kW | 10 | 3,400 kWh |
| 4-bed detached | 3,800–4,800 | 5 kW | 12–13 | 4,250 kWh |
| 5-bed / large detached | 4,800–6,000 | 6 kW | 14–15 | 5,100 kWh |
| Large home + EV / heat pump | 6,000–8,000 | 8 kW | 20 | 6,800 kWh |
Source: Ofgem typical domestic consumption values 2026, MCS Standard MIS 3002 generation estimates, Energy Saving Trust. Panel count assumes 400W monocrystalline panels at 35° pitch, south-facing.
Important: these are averages. If you work from home, have a heat pump, charge an EV, or run multiple appliances during the day, you'll use more electricity and may benefit from a larger system. Check your actual annual usage on your electricity bill before deciding.
The formula (calculate yourself)
If you want to work out the exact panel count for your specific situation, here's the formula every MCS-certified installer uses:
panels needed = annual usage (kWh) ÷ (panel wattage (kW) × sun hours × 0.7)
Where:
- Annual usage — from your electricity bill (look for "kWh used" over 12 months)
- Panel wattage — in kilowatts (400W = 0.4 kW)
- Sun hours — your region's annual peak sun hours (see table below)
- 0.7 — performance ratio (accounts for inverter losses, temperature, dust, wiring — the MCS standard assumption)
Worked example: 3-bed semi in London
- Annual usage: 3,400 kWh
- Panel wattage: 400W (0.4 kW)
- London sun hours: 1,015 hrs/year
- Performance ratio: 0.7
3,400 ÷ (0.4 × 1,015 × 0.7) = 3,400 ÷ 284 = 11.97 → 12 panels
So a London 3-bed semi needs 12 panels (round up, not down). That's a 4.8 kW system — slightly larger than the "typical 4 kW" because we're matching actual usage rather than using averages.
Our panel count calculator does this instantly — enter your annual usage and region to get your exact panel count, system size, roof area and estimated cost.
What panel wattage to choose
In 2026, residential solar panels come in three common wattages. Higher wattage means fewer panels — but higher cost per panel.
| Panel wattage | Panel count (4 kW system) | Cost per panel | Best for |
|---|---|---|---|
| 400W (standard) | 10 | £100–£150 | Most homes — best value |
| 450W | 9 | £130–£180 | Limited roof space |
| 500W | 8 | £160–£220 | Very limited roof space |
For most UK homes, 400W monocrystalline panels from tier-1 brands (JA Solar, Trina, Jinko, Aiko) offer the best balance of cost, efficiency and roof space utilisation. Premium brands (SunPower Maxeon, REC Alpha) cost 50–100% more but offer slightly higher efficiency and longer warranties (25–40 years vs 25).
Panel wattage has been creeping up — in 2020, 350W was standard; by 2026, 400W is the baseline. Don't buy panels below 400W in 2026 — they're outdated and the cost saving is negligible.
How much roof space do you need?
A typical 400W panel measures roughly 1.9 m × 1.1 m (about 1.9 m²). But you can't tile them edge-to-edge — installers need spacing for mounting rails, roof edges and maintenance access.
| System size | Panel count | Panel area | Recommended roof area |
|---|---|---|---|
| 3 kW | 7–8 | ~15 m² | 20–25 m² |
| 4 kW | 10 | ~19 m² | 25–30 m² |
| 5 kW | 12–13 | ~25 m² | 30–35 m² |
| 6 kW | 14–15 | ~29 m² | 35–40 m² |
| 8 kW | 20 | ~38 m² | 45–55 m² |
The "recommended roof area" is larger than panel area because of: edge margins (200mm minimum), spacing between rows, chimney/dormer obstructions, and access for maintenance. A typical UK semi-detached roof has 25–35 m² of usable south-facing space — enough for a 4–5 kW system.
What if your roof is too small?
- Use higher-wattage panels (450W or 500W) — fewer panels, same output
- Use both roof faces (east-west split) — generates slightly less but uses more of your roof
- Accept partial coverage — a 3 kW system still saves £400–500/year, just doesn't cover 100% of usage
- Consider ground-mounted if you have garden space — costs ~20% more but no roof constraints
Does your region change the count?
Yes — significantly. The UK has a 20%+ difference in sun hours between the sunniest and least sunny regions. The less sun you get, the more panels you need for the same electricity.
| Region | Annual sun hours (PVGIS) | Panels for 3,400 kWh (400W) | System size |
|---|---|---|---|
| South East | 1,077 | 11 | 4.4 kW |
| South West | 1,113 | 11 | 4.4 kW |
| East of England | 1,040 | 12 | 4.8 kW |
| London | 1,015 | 12 | 4.8 kW |
| East Midlands | 986 | 12 | 4.8 kW |
| West Midlands | 960 | 13 | 5.2 kW |
| Yorkshire | 967 | 13 | 5.2 kW |
| Wales | 931 | 13 | 5.2 kW |
| North West | 942 | 13 | 5.2 kW |
| North East | 902 | 14 | 5.6 kW |
| Northern Ireland | 931 | 13 | 5.2 kW |
| Scotland | 840 | 15 | 6.0 kW |
Source: PVGIS 5.2 (European Commission, 2005–2020 baseline), verified July 2026. Panel count rounded up to nearest whole panel. Assumes 400W panels, 35° pitch, south-facing, 0.7 performance ratio.
The gap is real: a Scottish home needs 4 more panels than a South East home for the same electricity. But every UK region generates enough to make solar worthwhile — even Scotland exceeds 800 kWh/kWp.
Does roof direction matter?
Yes, but less than most people think. South-facing is optimal, but east-west roofs are genuinely viable in the UK.
| Roof direction | Generation vs south-facing | Panel count adjustment | Best for |
|---|---|---|---|
| South | 100% (baseline) | — | Maximum generation |
| South-east / South-west | ~95% | +0–1 panel | Almost as good as south |
| East / West | ~80–85% | +1–2 panels | Better morning/evening match |
| North-east / North-west | ~70% | +3–4 panels | Marginal — consider ground-mount |
| North | ~60–65% | Not recommended | Avoid unless no alternative |
East-west roofs have a hidden advantage: they generate more in the morning and evening, which better matches when most households actually use electricity. A south-facing roof peaks at midday when many homes are empty; an east-west split serves breakfast and dinner usage better.
Can you have too many panels?
Yes — and this is a common mistake. Adding panels beyond your usage doesn't save you more money; it just creates more surplus to export at low SEG rates.
The maths is simple: every kWh you self-consume is worth 26p (the electricity you don't buy). Every kWh you export is worth 3–15p (SEG rate). So generating surplus is worth 2–8× less than generating what you use.
Without a battery, self-consumption is typically 45%. That means if your panels generate 4,000 kWh, you use ~1,800 kWh (saving £468) and export ~2,200 kWh (earning £66–£330 at SEG). The export income is nice but much less valuable than self-consumed savings.
Rule of thumb: size your system to generate roughly 100–120% of your annual usage. The extra 20% covers export at SEG rates and gives you buffer for future usage growth (EV, heat pump). Beyond that, add a battery rather than more panels.
Frequently asked questions
How many solar panels do I need for a 3-bed house?
A typical 3-bed UK home needs 10–12 solar panels (a 4 kW system) to cover most of its electricity usage. This assumes ~3,400 kWh annual consumption, 400W panels, and average UK sun hours. In Scotland you may need 12 panels; in southern England 10 may suffice.
How do I calculate how many solar panels I need?
Divide your annual electricity usage (kWh) by the annual generation of one panel (panel wattage in kW × your region's sun hours × 0.7 performance ratio). Example: 3,400 kWh ÷ (0.4 kW × 1,015 hrs × 0.7) = 12 panels for a London home using 400W panels.
How much roof space do I need?
A typical 400W panel is about 1.9 m². A 10-panel (4 kW) system needs roughly 19 m² of usable roof space. Allow extra for spacing — most installers recommend 25–30 m² of total roof area for a 4 kW system.
Can I have too many solar panels?
Yes. If your panels generate more than you use and export, you're selling surplus at SEG rates (3–15p/kWh) while buying back at 26p/kWh. Oversizing without a battery wastes value. Match panel count to your daytime usage, or add a battery to capture surplus.
What wattage solar panel should I buy?
In 2026, 400W is the standard residential panel. 450W and 500W panels are available and reduce panel count, but cost more per watt. For most UK homes, 400W monocrystalline panels from tier-1 brands offer the best balance.
Do solar panels work on east-west roofs?
Yes. East-west roofs generate about 15–20% less than south-facing, but produce more evenly across the day — better matching morning and evening usage. You typically need 1–2 extra panels to match a south-facing system's output.