Office Solar Case Study
NHS Trust HQ — 580 kWp Salix PSDS-funded install
NHS Trust HQ — 580 kWp Salix PSDS-funded install
A North-West NHS Trust administrative HQ of 14,500 sqm was due for EPC renewal in 2027 with the existing 2017-issued “C” rating widely expected to slip to “D” or “E” under SAP 10.2 methodology. The Trust applied to Salix PSDS Phase 4 with our support, securing a 100% capex grant for solar PV, battery storage, and LED relighting as part of a wider decarbonisation programme. We designed the 580 kWp system to deliver the maximum EPC uplift achievable within the building’s structural capacity.
The numbers
| Metric | Value |
|---|---|
| System size | 580 kWp PV + 250 kWh battery |
| Panel count | 1075 |
| Annual generation | 534,000 kWh/year |
| Annual saving | £164,000/year |
| Simple payback | 0 years |
| Annual CO₂ saved | 122 tonnes |
| EPC uplift | D → B (12-point gain) |
| Completion | Q2 2025 |
The Salix PSDS application process
The Trust applied to Salix PSDS Phase 4 (January 2024 window) with our support. PSDS applications require: a board-approved decarbonisation pathway document, a Heat Decarbonisation Plan (HDP) prepared by a qualified assessor, a competitive procurement evidence pack for the proposed contractor, a detailed capital and operational cost-benefit analysis, and alignment with the Salix programme’s minimum CO₂ savings threshold (typically £30-£60 of grant per tonne of CO₂ saved over 20 years).
We prepared the solar-specific sections of the Trust’s PSDS application alongside their M&E consultants who handled the HDP. Our contribution covered: the PVSyst-modelled yield data and uncertainty analysis, a capital cost breakdown using NEC4 contract terms (PSDS requires NEC contract for awards over £1m), the CO₂ savings calculation in the format specified by the Salix application template, and a delivery programme aligned with the PSDS milestone payment structure (typically 25% on contract award, 25% on commencement on site, 50% on practical completion).
The application was awarded £1.2m in grant funding covering 100% of the PV and BESS capex. The LED relighting element (a further £180k) was funded separately via the Trust’s capital planning fund.
Project approach
With grant funding secured, the project design phase moved rapidly. Half-hourly meter data for the 14,500 sqm building — covering the main 8-storey administrative tower and a 2-storey annex — showed a high and stable 24/7 baseload of 95 kW, reflecting the server and comms infrastructure supporting the Trust’s clinical systems. Daytime occupancy peaks added a further 40-80 kW.
PVSyst modelling for the North-West site (latitude 53.6°N) and the specific roof geometry confirmed a 580 kWp array would generate 534,000 kWh/year with a self-consumption ratio of 88% against the building’s demand profile — the 250 kWh BESS capturing surplus midday generation and shifting it to the early-morning and evening peaks. The EPC impact was modelled at 12 SAP points under SAP 10.2 — taking the expected 2027 re-assessment rating from D to B and satisfying the Trust’s NHS Net Zero Estate target (all NHS buildings to EPC B or above by 2030).
Roof, structural, and electrical
The 8-storey administrative tower has a reinforced concrete flat roof. Structural assessment per BS EN 1991 confirmed sufficient load capacity for ballasted aluminium racking; a dedicated structural engineer’s sign-off was included in the PSDS application as required by Salix. East-west landscape arrays were specified across the tower roof; south-facing arrays on the lower 2-storey annex.
The 580 kW DC array was aggregated into six 100 kW string inverters with a centralised SCADA monitoring system — required by the Trust’s facilities management protocol for all generation assets over 100 kW. The 250 kWh BESS was installed in a dedicated plant room on the third floor, avoiding ground-floor flooding risk. G99 application was submitted to Electricity North West (ENW) with a 60 kW export limit — well within the headroom available on the Trust’s HV supply — approved in nine weeks.
Compliance, EPC and reporting
The system was installed to MCS Commercial standards under NEC4 Engineering and Construction Contract terms (required for PSDS compliance). NICEIC electrical certification and RECC documentation were provided. Commissioning followed IEC 62446 with witnessed string testing and performance documentation submitted to Salix as part of the grant practical completion pack.
Post-commissioning EPC assessment confirmed the D → B (12-point gain) outcome. The B-rated EPC was submitted to NHS England as part of the Trust’s Annual Sustainability Report and to NHSE’s Estates Return Information Collection (ERIC) database.
For NHS Scope 2 reporting, we provided a disclosure pack aligned with Greener NHS reporting requirements: GHG Protocol Scope 2 calculations (both location-based and market-based using the NHS Zero Carbon programme’s market-based conversion factors), a SECR-ready narrative, and a pre-populated Sustainable Development Assessment Tool (SDAT) entry covering the solar installation.
What the customer said
“The 100% PSDS grant meant zero capex impact on our annual budget while delivering the Trust’s largest single Scope 2 emissions reduction in the operational decarbonisation roadmap.”
Could your NHS or public sector building deliver similar results?
The economics on this project aren’t unusual for a well-designed office solar install in 2026. What varies between buildings is the specific load shape, roof area, electrical infrastructure age, tenancy structure, and applicable grant or finance routes.
The fastest way to understand your specific economics is a free desk feasibility study. Send us half-hourly meter data and a roof plan, and we’ll model your building specifically within 7 working days.