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Solar PV Array Calculator
Calculate solar panel array size, annual energy yield and installation costs based on UK regional irradiance, roof orientation and panel specifications.
Panels in the array
30-35° is optimal for UK
Supply cost per panel
Typical: 0.3-0.5% per year
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How We Calculate This
This calculator estimates solar PV array output using UK regional irradiance data drawn from the MCS solar PV standard (MIS 3002) and SAP Appendix H, which bundle a 0.8 performance ratio into the kWh/kWp figure.
The formula
Annual yield = System kWp × Regional yield × Orientation × Pitch × Shading
- Regional yield: 850-1050 kWh/kWp depending on UK location (MCS MIS 3002 / SAP irradiance data; UK average ≈ 950)
- Orientation factor: south 100%, south-east/south-west 95%, east/west 80%, flat 85% (per SAP Appendix H orientation data)
- Optimal pitch: 30-35° for UK latitude
- Panel degradation: ~0.3-0.5% per year (crystalline silicon, NREL); the 25-year average applies compound degradation
- CO₂ saving uses the UK grid electricity factor of 0.131 kgCO₂e/kWh (DESNZ/DEFRA 2026 GHG conversion factors, published June 2026)
Frequently Asked Questions
A typical 400W solar panel produces approximately 380-420 kWh per year in the UK, depending on location, orientation and shading. South-facing panels at 30-35° pitch in southern England produce the most. A 10-panel (4 kWp) system typically generates 3,500-4,200 kWh/year.
A typical UK household uses 3,500-4,500 kWh/year. A 4 kWp system (10 panels) covers most of this but you won't use all generation directly. With a battery, you can store excess for evening use. Oversizing slightly (5-6 kWp) is common to maximise self-consumption and export income.
Modern 400W panels are approximately 1.75m² each. A 4 kWp system (10 panels) needs about 17.5m² of roof space. A 6 kWp system (15 panels) needs about 26m². Allow extra space for setbacks from roof edges (typically 300mm).
Yes, significantly. South-facing is optimal (100% yield). South-east/south-west reduces yield by about 5%. East or west facing reduces yield by about 20%. East-west split arrays can be worthwhile for self-consumption as they spread generation across the day.
Modern solar panels have a design life of 25-30 years with performance warranties guaranteeing at least 80% output at 25 years. Actual degradation is typically 0.3-0.5% per year. Inverters last 10-15 years and may need replacing once during the panel lifetime.
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Last updated: June 2026
Verified against UK standards · estimates only, confirm with your supplier.