Commercial Solar Worked Examples
Modelled scenarios — illustrative, not real projects — showing system size, financing route, payback and outcome bands by property type.
300 kW rooftop scenario — Tier-1 automotive supplier, West Midlands (modelled)
A precision-engineered components plant running double shifts six days a week. Annual electricity demand 1.4 GWh against escalating £140k-plus quarterly bills. The scenario models the existing 4,500 sqm composite roof from drawings, assumes a structural recalculation against the original 1998 design, and sizes a 300 kW system at 92% self-consumption for a 4.8-year payback.
- System
- 300 kW
- Modelled annual saving
- £68,000
- Payback
- 4.8 years
Modelled outcome: Modelled: installation over a four-week shutdown; first-year output within the forecast band; a second-phase 200 kW battery is the natural follow-on where evening load grows. Illustrative — not a real project.
120 kW roof scenario — multi-academy trust secondary school, East Midlands (modelled)
An 1,100-pupil secondary school within a six-academy MAT, modelled with a Phase-4-era Public Sector Decarbonisation Scheme award covering 100% of capital (PSDS has had no open window since November 2024; a new project would use capital budget, a PPA or a lease). A 120 kW classroom-block array with curriculum-integrated monitoring, term-time-only working over a five-week summer window.
- System
- 120 kW
- Modelled annual saving
- £21,500
- Payback
- 0 years
Modelled outcome: Modelled: fully grant funded in the scenario; live monitoring data usable in physics, geography and design technology; the model scales to further sites. Illustrative — not a real project.
650 kW PPA scenario — logistics distribution centre, South East (modelled)
A 12,000 sqm regional distribution centre on a 22p/kWh five-year fixed contract due to expire. The owner wants zero capital, no balance-sheet treatment and a fixed energy rate below grid. The scenario models a 20-year PPA — an installer-owned 650 kW rooftop system with an 11p/kWh fixed rate to the host plus a profit share on export.
- System
- 650 kW
- Modelled annual saving
- £72,000
- Payback
- 0 years
Modelled outcome: Modelled: zero capital, a fixed 11p/kWh energy rate for 20 years, and around 130 tonnes/year of carbon reduction reportable in the ESG report from year one. Illustrative — not a real project.
How these worked examples are built
Every scenario above is modelled — this site is an independent publisher and does not install, so it holds no customer data and claims no measured results. Each example takes the sector's typical demand profile, this site's published cost-per-kWp and yield bands, and a stated tariff, and works the arithmetic through to saving and payback. Labels say "modelled" because they are.
Use them to calibrate expectations before you read an installer's proposal: if a quote promises a payback well inside the band for your sector, ask what self-consumption ratio and tariff it assumes. The four-to-seven-year range across these scenarios reflects typical UK conditions on capital purchase, not best-case modelling — and a grant-funded scenario is labelled as such.