220 kW Solar + Air-Source Heat Pump Bundle — Bristol FE College, 100% PSDS Phase 4
- System size
- 220 kW
- Annual saving
- £56,000
- Payback
- 4.2 years
- Location
- Bristol, South West
Scenario
A general FE college in central Bristol, serving roughly 6,800 16-19 learners plus a substantial apprenticeship and adult provision, sat on a campus dominated by a 1960s main teaching block and a 1980s annex. Both buildings were heated by ageing gas boilers approaching end of warranted life, and the college’s 2024-25 combined gas + electricity bill ran to £710,000 against a backdrop of South West regional electricity rates that had risen 31% in real terms since 2021.
The college’s Sustainability Lead, in post since the corporation adopted its Climate Action Plan in October 2024, had been tracking the Phase 4 application window for the Public Sector Decarbonisation Scheme (PSDS) since launch. The Phase 4 brief explicitly favoured integrated heat-decarbonisation + low-carbon-generation bundles over standalone solar — and the college’s gas boilers were close enough to end-of-life that the corporation could credibly include heat decarbonisation in the same bid.
The Phase 4 application was prepared as a bundled package: a 600 kW air-source heat pump array sized to replace the main and annex boilers, plus 220 kW of rooftop solar sized to offset a meaningful share of the new electrical load created by the heat pumps. The integrated economics were materially stronger than either intervention standalone — the heat pumps reduced gas demand and lifted electrical demand, and the solar took the edge off the new electrical demand and protected the long-run economics from electricity price drift.
This case study is an illustrative composite based on representative FE college PSDS bundled-bid engagements. Specific identifying details are anonymised.
What we delivered (solar element)
Total solar system: 220 kW across two roof envelopes, designed to integrate with the heat pump load profile.
- Main teaching block (south-east aspect membrane): 140 kW (256 × 545 W panels, 14° tilt, mechanically fixed, two string inverters in main plant room shared with the heat pump cascade)
- 1980s annex (south-aspect pitched tile): 80 kW (146 × 545 W panels, single string inverter)
- No battery on this scheme — the heat pumps act as a controllable load that follows generation, so PV-direct self-consumption modelled at 86% without storage and the corporation’s capital was prioritised on extending the heat pump array coverage
The heat pump element (delivered by our heat-decarbonisation partner) was scoped, costed and submitted under the same PSDS Phase 4 bid. We led the bid authorship and the technical-design integration across both elements.
DBS-cleared install crews across both subsystems. KCSIE 2025 safeguarding induction by the Deputy Principal at programme kick-off.
Funding stack — 100% PSDS Phase 4
This is the case for PSDS Phase 4 done properly. The bundled bid cleared the funding panel on first submission:
- PSDS Phase 4 grant: £880,000 covering the full bundled capex (solar £200,000 at £909/kW; heat pumps and ancillaries £680,000)
- Solar capital cost: £200,000 at £909/kW
- Modelled annual solar energy savings: £56,000
- Modelled annual gas-displacement savings (heat pumps): £142,000
- Combined modelled annual saving: £198,000
- Corporation capital contribution: zero
- Year-one cash position: £198,000 positive (no loan service, fully grant-funded capex)
- Total 25-year nominal benefit on the bundled bid: £5.4m (real-terms model, before gas price drift)
- Solar-element-only payback: 4.2 years (notional, against the grant value — actual corporation payback is zero years because PSDS is non-repayable)
The PSDS Phase 4 application leaned on the college’s published Climate Action Plan, the integrated decarbonisation rationale (heat + generation in one bid), the boiler end-of-life timing, and the DfE Sustainability and Climate Change Strategy alignment. Salix administered the PSDS application and confirmed acceptance in 13 weeks. Corporation approval was recorded in a single board minute under the Climate Action Plan agenda item.
Programme and compliance
- Summer 2026 build window: solar scaffold up 8 July; panels live 18 August; heat pump cascade commissioned in parallel and brought on-line 28 August, ahead of the autumn term heating-season start
- G99 DNO application: the bundled load picture mattered — the application went in with the heat pump electrical demand modelled alongside the solar export, so the DNO sized the connection upgrade once. Accepted at 15 weeks
- Asbestos R&D survey clear on the 1960s main block at roof level; one Type 3 enclosed protocol penetration on the 1980s annex
- Structural engineer survey on both roofs; the 1960s main block carried sufficient capacity for the panel array without strengthening
- Heat pump plant room sized in the same programme as the solar inverter cabinets, sharing controls infrastructure
- KCSIE 2025 safeguarding induction at every contractor mobilisation
- ESFA Post-16 Audit Code: PSDS grant drawdown lodged as an auditable workpaper; corporation board minute formally records the grant agreement
Outcomes
- Year-one actual solar generation: 5% above design model
- Year-one actual solar energy savings: £58,800 versus modelled £56,000 (+5.0%)
- Year-one heat pump performance: actual SCOP 3.1 versus modelled 2.9 (favourable winter weather pattern); gas-displacement savings landed at £155,000 vs modelled £142,000
- Combined year-one actual saving: £213,800 against the £198,000 model
- EAUC Scorecard: moved the college from “Silver” to “Gold” on the Operations and Estates module
- AoC Climate Action Plan reporting integration — both solar generation and heat pump runtime feed into the corporation’s quarterly KPI pack
- DfE Sustainability and Climate Change Strategy: the project was used as a featured case study in the regional DfE south-west FE cluster meeting in November 2026
- Phase 2 conversation: the corporation has opened scoping on a 90 kW car-park canopy under the next PSDS or Salix window, drawing on the same bid team
What the Sustainability Lead said
“PSDS Phase 4 isn’t for solar-only bids. The funding panel wants integrated decarbonisation. The way we got the full £880k across the line was packaging the heat pumps and the solar as one technically integrated bid — the heat pumps create the new electrical load and the solar offsets it, so the economics hang together as one scheme rather than two unrelated capital asks. Corporations that go in with a standalone solar bid through PSDS are leaving the better grant on the table.”