Commercial Solar PV ROI Calculator 2025/26
Calculate the return on investment for a commercial rooftop solar PV installation in 2025/26. Enter system size, roof orientation, self-consumption rate and local electricity price to see annual generation, savings, SEG income and payback period.
Key Inputs
- Roof area available (m²) and orientation (south-facing optimal; east/west reduces output by ~20%)
- System size (kWp) — approximately 5-6 m² per kWp of panels
- Installation cost per kWp (£700-£900 for commercial installations)
- Self-consumption percentage (typically 30-50% for commercial premises)
- Export percentage (50-70% of generation exported to grid)
- Current electricity buy price (p/kWh)
- SEG export rate offered by your supplier (p/kWh — ranges 3-15p)
What You'll Get
- Annual generation estimate (kWh) — south-facing: 850-1,000 kWh/kWp/year in England
- Annual self-consumption saving (£) — units generated and used onsite
- Annual SEG export income (£) — units exported to grid at SEG rate
- Total annual benefit (£)
- Simple payback period (years)
- CO2 saved per year (tonnes)
Important Notes — 2025/26 Rates & Caveats
UK commercial solar benchmarks 2025: 4kW residential system £4,000-£6,000; 50kW commercial system £25,000-£40,000; 250kW industrial system £100,000-£150,000. Generation: a south-facing roof in England generates 850-1,000 kWh per kWp per year. East/west facing reduces output by approximately 20%. Smart Export Guarantee (SEG) rates vary by supplier from 3p to 15p/kWh — Octopus Agile and similar variable tariffs can exceed this. Commercial solar attracts standard 20% VAT (residential solar is 0% VAT from April 2022). Corporation Tax capital allowances can significantly improve the commercial return.
Frequently Asked Questions
How much electricity does a 50kW commercial solar system generate per year?
Approximately 42,500-50,000 kWh/year on a south-facing roof in south England — enough to power a small retail unit or office building. Generation is lower for east/west-facing roofs (typically 34,000-40,000 kWh). A north-facing roof is generally not economically viable for solar in the UK. Output is also affected by shading, pitch angle and local weather patterns.
What is the Smart Export Guarantee (SEG)?
The Smart Export Guarantee (SEG) is the UK government scheme that requires licensed energy suppliers with more than 150,000 customers to offer a tariff for electricity exported to the grid from small-scale renewable generators (up to 5MW). SEG rates are set by suppliers and range from approximately 3p to 15p/kWh depending on the supplier and tariff type. Variable tariffs linked to wholesale prices can pay significantly more during peak demand periods.
Is commercial solar installation VAT-exempt?
No — commercial solar installations attract standard 20% VAT. Residential solar (on domestic properties) qualifies for 0% VAT from April 2022. However, commercial businesses can reclaim the VAT on their solar installation as input VAT through their VAT return, provided the system is used for business purposes. This effectively makes the VAT cost neutral for VAT-registered businesses, improving the economics compared to non-VAT-registered organisations.
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