Size photovoltaic systems and calculate generation, costs, and payback for UK installations
Size a photovoltaic system for your UK property
Understanding current UK energy prices is essential for calculating solar panel savings and payback periods. Prices have stabilized in 2025 but remain significantly higher than pre-2020 levels.
Electricity Import Costs:
Smart Export Guarantee (SEG) Export Rates:
Key Insight: Every kWh you generate and use yourself saves £0.27 (not bought from grid). Every kWh exported earns £0.05-0.15. This is why maximizing self-consumption is critical for ROI.
| Home Type | Annual Usage | Annual Cost @ £0.27/kWh | Recommended Solar |
|---|---|---|---|
| Small flat/1-2 bed | 1,800-2,400 kWh | £486-648 | 2-3 kW (8-10 panels) |
| Medium house/2-3 bed | 2,700-3,500 kWh | £729-945 | 3-4 kW (10-14 panels) |
| Large house/4+ bed | 4,000-6,000 kWh | £1,080-1,620 | 5-7 kW (16-22 panels) |
| Large house + EV | 6,000-10,000 kWh | £1,620-2,700 | 7-10 kW (22-32 panels) |
Usage includes heating, hot water, appliances, lighting, and EV charging where applicable
UK solar panel installation costs have decreased significantly since 2010 while panel efficiency has improved. Here's what to expect in 2025.
| System Size | Panels Needed | Total Cost | Cost per kW | Annual Generation |
|---|---|---|---|---|
| 2 kW | 5-6 panels | £4,000-5,000 | £2,000-2,500 | 1,700-2,000 kWh |
| 3 kW | 8-10 panels | £5,000-6,500 | £1,667-2,167 | 2,550-3,000 kWh |
| 4 kW | 10-13 panels | £6,000-8,000 | £1,500-2,000 | 3,400-4,000 kWh |
| 5 kW | 13-16 panels | £7,000-9,500 | £1,400-1,900 | 4,250-5,000 kWh |
| 6 kW | 15-18 panels | £8,000-10,500 | £1,333-1,750 | 5,100-6,000 kWh |
| 8 kW | 20-24 panels | £10,000-13,000 | £1,250-1,625 | 6,800-8,000 kWh |
Prices include MCS-certified installation, scaffolding, electr ical work, and VAT at 0% (domestic only)
💰 2025 Savings: No VAT on solar panel installations for domestic properties (0% VAT). This saves 20% compared to commercial rates. Budget systems have also become more competitive.
These worked examples use real 2025 UK energy prices and installation costs to show accurate payback periods and 25-year returns.
Scenario:
Annual Generation:
4 kW × 850 kWh/kW = 3,400 kWh/year
Self-Consumption Analysis:
Assuming 40% self-consumption (typical without battery):
• Self-consumed: 3,400 × 40% = 1,360 kWh @ £0.27 = £367 saved
• Exported: 3,400 × 60% = 2,040 kWh @ £0.12 SEG = £245 earned
Total annual benefit: £612
Payback Calculation:
Installation cost: £7,000
Annual savings: £612
Payback period: 11.4 years
25-Year Return:
Annual savings: £612 × 25 years = £15,300
Minus installation: £15,300 - £7,000 = £8,300 profit
Assuming 0.5% annual degradation and flat energy prices (conservative)
✓ Result: 11.4-year payback, £8,300 profit over 25 years (119% ROI)
Scenario:
With Battery Storage:
• Self-consumed: 3,400 × 65% = 2,210 kWh @ £0.27 = £597 saved
• Exported: 3,400 × 35% = 1,190 kWh @ £0.12 SEG = £143 earned
Total annual benefit: £740
Payback vs Without Battery:
With battery: £11,000 ÷ £740 = 14.9 years
Without battery: £7,000 ÷ £612 = 11.4 years
Battery adds 3.5 years to payback but increases long-term returns
25-Year Comparison:
With battery: (£740 × 25) - £11,000 = £7,500 profit
Without battery: (£612 × 25) - £7,000 = £8,300 profit
Note: Battery may need replacement after 10-15 years (£2,000-3,000 cost)
⚡ Verdict: Battery adds comfort (power during evening) but slower ROI unless energy prices rise significantly
Scenario:
Annual Generation:
7 kW × 850 kWh/kW = 5,950 kWh/year
With Smart EV Charging (daytime):
EV charges during sunny hours (50% self-consumption possible):
• Self-consumed: 5,950 × 50% = 2,975 kWh @ £0.27 = £803 saved
• Exported: 5,950 × 50% = 2,975 kWh @ £0.12 SEG = £357 earned
Total annual benefit: £1,160
Excellent Payback:
Installation cost: £10,000
Annual savings: £1,160
Payback period: 8.6 years
25-Year Return:
(£1,160 × 25) - £10,000 = £19,000 profit (190% ROI)
✓ Best ROI: Larger systems with high daytime usage (especially EV charging) offer fastest payback
Solar photovoltaic (PV) panels convert sunlight into electricity. Even on cloudy days, UK solar panels generate power, making them a viable renewable energy solution across all regions.
Annual averages. Summer generation 3-5× winter generation.
MCS (Microgeneration Certification Scheme) is essential for UK solar installations. It ensures quality, provides consumer protection, and is required for SEG payments.
MCS is a quality assurance scheme for renewable energy installations. Only MCS-certified installers can install systems that qualify for SEG (Smart Export Guarantee) payments.
Usually Permitted Development: Most domestic rooftop solar installations don't require planning permission.
Always check with your local planning authority before installation.
Solar PV installations must comply with BS 7671 Section 712:
The Smart Export Guarantee (SEG) requires electricity suppliers to pay for renewable energy exported to the grid. All MCS-certified systems are eligible.
When your solar panels generate more electricity than you use, the excess is exported to the National Grid. Your energy supplier pays you for this exported energy.
Important: SEG rates vary by supplier. Shop around for best rates. Some tariffs track wholesale prices and can be higher during peak times.
Key principle: Using solar energy yourself saves more than exporting it.
Strategy: Use appliances during sunny hours (dishwasher, washing machine, EV charging) to maximize self-consumption. Battery storage increases self-consumption from ~30% to ~70%.
Always verify MCS certification for panels and inverters to qualify for SEG.