Planning to install solar panels at home but not sure how many you need? The answer depends on your household’s energy use, roof size, and future plans. While most UK homes require around 10–14 panels, this guide will help you estimate the right system size for your property and understand what factors to consider before installation.
Real-Life Example
The Davies family from Llandeilo have a four-bedroom detached home using 4,800 kWh per year. After installing a 13-panel solar system, they now cover 92% of their annual electricity needs. Their battery stores excess energy for evening use, so they only buy electricity during the coldest winter months.
Step-by-Step Calculation for Wales
1. Find Your Annual Electricity Usage (kWh)
This is the most important starting point — you’ll find it on your electricity bill.
UK averages (Ofgem 2024):
- Small, energy-efficient flat: 1,800–2,000 kWh per year
- Typical 3-bedroom house: 3,100–4,200 kWh per year
- Large home with electric heating or EV: 8,000–12,000+ kWh per year
For this example, let’s use a typical 3-bedroom Welsh home consuming
3,600 kWh per year.
2. Estimate Your Ideal System Size (kWp)
We can estimate system size using this simplified formula, adjusted for Welsh solar conditions:
System size (kWp) = Annual electricity use (kWh) ÷ (Annual sunlight hours × System efficiency)
- Average annual sunlight hours in Wales: 3.0 hours/day × 365 = 1,095 hours
- System efficiency: typically 85% (0.85), accounting for inverter and temperature losses
Calculation:
3,600 ÷ (1,095 × 0.85) = 3,600 ÷ 930 = ≈ 3.9 kWp
3. Calculate How Many Panels You Need
Modern high-efficiency panels in the UK range from 350W–450W.
Number of panels = System size (kW) ÷ Panel wattage (kW)
Using a 415W (0.415 kW) panel:
3.9 ÷ 0.415 = ≈ 9.4 panels
You’d therefore need around
10 panels to meet this household’s annual electricity needs — forming a 4 kWp system.
Result Summary
| Description |
Value |
| Annual usage |
3,600 kWh |
| Average Welsh sunlight |
1,095 hours |
| System size |
~3.9 kWp |
| Panel size |
415W |
| Panels needed |
10 |
| Roof area required |
18–20 m² (approx.) |
In short: A typical three-bedroom home in Wales would need around 10 high-efficiency panels (≈4 kWp) to meet its annual energy needs, depending on roof orientation and lifestyle.
Recommended System Size by Property Type
| Property Type |
Recommended System |
Panels (440–450W) |
Roof Space Needed |
| 1–2 bed terraced |
2.5 kW |
6 |
10–12 m² |
| 3 bed semi-detached |
4 kW |
9 |
16–18 m² |
| 4 bed detached |
5.5 kW |
13 |
23–26 m² |
| 5+ bed detached |
8 kW+ |
18+ |
32 m²+ |
Expected Annual Energy Generation
| Property Type |
Annual Generation |
| 1–2 bed terraced |
2,125–2,250 kWh |
| 3 bed semi-detached |
3,400–3,600 kWh |
| 4 bed detached |
4,675–5,000 kWh |
| 5+ bed detached |
6,800–7,200+ kWh |
UK & Wales-Specific Considerations
1. Roof Orientation Matters
- South-facing (ideal): Generates the most electricity.
- East or West-facing (good): Expect around 15–25% lower efficiency — you may need one or two extra panels.
- North-facing: Usually not cost-effective for solar PV.
2. Smart Export Guarantee (SEG)
Under the UK’s SEG scheme, you’re paid for the surplus electricity your system exports to the grid.
- Typical rates: 1p–15p per kWh exported
- Grid import cost: around 28p per kWh
It’s therefore more beneficial to use your solar energy in real time — for example, by running appliances during daylight hours.
Enhance Your System with Battery Storage
“Adding battery storage was the best decision we made. During an October storm, our lights stayed on while neighbours were in the dark. The system paid for itself that week alone.”
— The Morgan Family, Brecon (8.2kW system with 13.5kWh storage)
Battery Benefits
- Use solar energy at night and during peak times
- Charge your EV from stored solar power
- Backup during power cuts
- Optimise costs using smart tariffs
Your Action Plan
- Check your energy bills – find your exact annual kWh usage.
- Use a UK calculator – the Energy Saving Trust offers reliable solar sizing tools.
- Get local quotes – trusted Welsh installers can:
- Use satellite data to assess your roof’s tilt, direction, and shading
- Provide accurate generation forecasts for your location
- Advise on the best SEG tariffs and battery options
Choosing the right solar panel setup isn’t about guessing — it’s about understanding how your home uses energy and what your roof can deliver. Taking time to match your system size to your real needs means better performance, lower costs, and a smoother path to long-term savings. Whether you’re just starting your research or ready to plan, understanding your ideal system size is the best first step towards making solar work for you.
