180 kW Sixth Form College Solar — Cambridge / East of England, Salix-Funded
- System size
- 180 kW
- Annual saving
- £39,000
- Payback
- 6 years
- Location
- Cambridge, East of England
Scenario
A standalone sixth form college on the southern edge of Cambridge, serving roughly 1,250 students across A-level and Level 3 BTEC programmes, was approaching a contract break point on its electricity supply in October 2026. The Principal and Finance Director had jointly chaired a working group through the spring term tasked with returning a Climate Action Plan to corporation in line with the AoC and EAUC Climate Action Roadmap (Nov 2024) and the DfE Sustainability and Climate Change Strategy.
The college’s 2024-25 electricity bill had landed at £448,000 — a 38% rise on the 2021-22 baseline once contract rollovers and CCL increases were stripped out. 16-19 base rate funding had not moved to compensate. The corporation’s reserves position was strong but the board’s Resource Committee had been clear it would not approve unfunded capital outflow for an energy project when external financing was available.
A 280 kW feasibility study commissioned by the working group had returned a mixed picture — three of the four candidate roof slopes carried good orientation and modern membrane, but the fourth (an early-1990s pitched-tile teaching block) failed structural sign-off without strengthening that would have pushed the project outside payback bounds.
This case study is an illustrative composite based on representative sixth form college engagements. Specific identifying details are anonymised.
What we delivered
Total system: 180 kW across two roof envelopes on the main teaching campus, sized to fit the constrained roof inventory without compromising payback.
- Main teaching block (south-east aspect membrane): 110 kW (202 × 545 W panels, 14° tilt, mechanically fixed, 1 string inverter in adjacent plant room)
- Sports hall (south-west aspect standing seam): 70 kW (128 × 545 W panels, 5° tilt, clamp-mounted no roof penetration, 1 string inverter in sports-hall plant cupboard)
- No battery — the load profile is heavily aligned with generation (07:30-17:00 weekday teaching) so self-consumption modelled at 89% without storage; battery payback failed to clear the corporation’s 8-year hurdle
- Live-generation dashboard in main reception and a secondary kiosk in the LRC, with weekly CSV exports for A-level Environmental Science and BTEC Applied Science cohorts
DBS-cleared install crews. KCSIE 2025 safeguarding induction delivered by the Deputy Principal at programme kick-off. Single point of contact across both sub-systems.
Funding stack
100% Salix Decarbonisation Loan, sized to the full capex with no corporation cash contribution:
- Capital cost: £165,000 at £917/kW (single-college unit rate, reflecting the smaller programme scale vs the £880/kW achieved on multi-site group bids)
- Loan term: 8 years
- Annual repayment: £20,625
- Modelled annual energy savings: £39,000
- Net year-one cash position: £18,375 positive
- Total 25-year nominal benefit: £620,000 (real-terms model with modest electricity inflation; £790,000 at mid-case)
The Salix bid leaned on the college’s published Climate Action Plan and the DfE Sustainability and Climate Change Strategy alignment as the rationale, with energy savings auditable against historic half-hourly data from the contract holder. Salix returned an accepted decision in nine weeks. Corporation approval was recorded in the May 2026 board minute under a single agenda item.
Programme and compliance
- Summer 2026 install window: scaffold up 8 July, panels live and commissioned 21 August, three days before A-level results day and ahead of induction week
- G99 DNO application submitted at design lock — accepted at 14 weeks with the DNO requesting only a minor export-limiter setting on one inverter (set to 70 kW)
- Asbestos R&D survey clear on the main teaching block; sports hall is post-2000 and cleared on documentation alone
- Structural engineer survey on both roofs — main teaching block accepted as-built; sports hall standing-seam required no strengthening with the clamp-mount approach
- KCSIE 2025 safeguarding induction at every contractor mobilisation
- ESFA Post-16 Audit Code: Salix energy savings calculation lodged as an auditable workpaper; corporation board minute formally records the loan agreement
Outcomes
- Year-one actual generation: 4.2% above design model
- Year-one actual energy savings: £40,600 versus modelled £39,000 (+4.1%)
- Featured in the college’s first Climate Action Plan progress update as the lead capital action
- EAUC Scorecard: moved the college from “Bronze” to “Silver” on the Operations and Estates module on first re-submission
- AoC Climate Action Plan reporting integration — generation and avoided-emissions figures fed directly into the corporation’s quarterly KPI pack from go-live
- Open-evening uptake on Environmental Science A-level rose 18% the September after install — the Curriculum Manager attributed part of this to the visibility of the generation dashboard and the live data feed into lessons
- Phase 2 conversation opened in autumn 2026 around adding a 40 kW carport canopy over the main staff car park, drawing on the same Salix relationship
What the Sustainability Lead said
“What sold this to the Resource Committee wasn’t the kWh number — it was the funding stack. Salix put up 100% of the capex, the loan repayments came in under our modelled savings, and from day one the project was cash-flow positive against the budget. We didn’t have to touch reserves and we didn’t have to bring it back to corporation for a second sign-off. That’s what makes solar the unlock for sixth form colleges that don’t have a multi-campus parent to spread risk across.”