Indicative outputs
- System size
- — kWp
- Panel count
- —
- Capex estimate
- £—
- Annual generation
- — kWh/year
- Annual saving
- £—
- Simple payback
- — years
- 25-year NPV (7% discount)
- £—
- EPC uplift
- —
- Annual CO₂ saved
- — tonnes
- MEES 2030 status
- —
Indicative only. We replace this with a full half-hourly meter data model in our free feasibility study.
How the calculator works
The model uses standard UK commercial solar PV economics and reasonable defaults:
- Sizing: system kWp = (sqm × 240 kWh/sqm/year × 0.75) / 920 kWh/kWp/year — covers ~75% of typical office annual demand
- Panels: 450W per panel, so kWp × 2.22 = panel count
- Capex: tiered cost-per-kWp (£1,000/kWp under 100, £900/kWp 100-500, £800/kWp 500+)
- Self-consumption: 78% (Mon-Fri offices), 85% with battery
- Annual saving: (self-consumed kWh × day rate) + (exported kWh × 9p/kWh SEG)
- NPV: 7% discount rate, 0.5% panel degradation/year, 2.5% electricity price escalation
- EPC uplift: 4-12 SAP points depending on system kWp:sqm ratio
- CO₂: 0.21 kg CO₂e per displaced grid kWh
The actual numbers for your building depend on roof geometry, shading, electrical infrastructure age, half-hourly load shape, and the specific finance structure chosen. Our free feasibility study uses 12 months of half-hourly meter data and PVSyst yield modelling — typically within 2-4% of the eventual measured performance.