Free tool · Updated 12 May 2026

Commercial solar payback calculator

Free interactive UK commercial solar payback calculator. Input your system size, current electricity rate, expected self-consumption and ownership structure — see instant year-1 savings, post-tax effective cost, and payback period.

Last reviewed 12 May 2026 2 min read By Donovan Fawcett Tool

Solar payback calculator

System size (kWp)

Capex £/Wp

Import rate (p/kWh)

Self-consumption %

SEG rate (p/kWh)

CT rate %

Your projected economics

System capex	£90,000
Year-1 tax relief	-£22,500
Net effective cost	£67,500
Annual generation	95,000 kWh
Annual self-consumption saving	£15,960
Annual SEG income	£3,040
Total annual savings	£19,000
Post-tax payback	3.6 years
25-year cumulative saving	£475,000

Indicative only. Real-world economics depend on roof type, DNO connection, system specification, and current SEG market rates. Use the free eligibility check for a personalised projection.

How to use this calculator

Five inputs drive the maths:

System size (kWp): Your planned system size. UK commercial typically 50-1,000 kWp.
Capex £/Wp: 2026 prices range £0.55-£1.20. Smaller systems higher; larger systems lower.
Import rate (p/kWh): Your current commercial electricity rate. Typical UK commercial 22-32p/kWh.
Self-consumption %: The fraction of generation consumed on-site. Hotels and factories 75-95%; warehouses 20-30%.
SEG rate (p/kWh): Current SEG tariff. 2026 range 3p-15p/kWh.
CT rate %: Your tax rate. Limited companies 19-25%; partnerships use partner's marginal IT rate.

Assumptions and caveats

The calculator uses these standard assumptions:

950 kWh/kWp annual generation (UK average)
100% Full Expensing / AIA in year 1 (instant tax relief)
Constant import and SEG rates over 25 years (real-world rates trend upward)
No system degradation (real systems degrade 0.5-0.7%/year)
No battery storage or REGO sales (additional revenue streams)
No O&M costs (typical £8-£15/kWp/year)

For a personalised projection accounting for your specific roof, DNO connection, location and ownership structure, use the free eligibility check.

Donovan Fawcett · Director, SEO Dons Ltd Twelve years in UK commercial solar SEO and grant advisory. Editorial policy & independence.

Want a personalised payback projection?

Free 60-second eligibility check returns a personalised funding shortlist plus indicative capex, payback and grant stack for your specific business.

Free eligibility check