Public sector · NHS · PSDS

NHS Trust PSDS Phase 4 application strategy — bundles that win

Update, 10 September 2026: Phase 4 was the final PSDS phase and closed to applications in November 2024, so no new bids can be made. The bundling logic below still applies to any successor scheme; for what NHS trusts can do now, see our guide to public sector solar funding routes.

Published 2026-04-22 · 10 minute read · By Commercial Solar Finance editorial team See our East Midlands NHS Trust PSDS case study for a worked example of a successful bundled portfolio application.

NHS Trust PSDS Phase 4 applications consistently outperform on cost-per-tonne when bundling solar with heat pumps and fabric efficiency across multi-site estate. Trust-level portfolio bids with 5+ sites consistently outscore single-site bids. We walk through the application strategy that wins.

PSDS Phase 4 was the final round and the NHS application pipeline was heavy. PSDS closed to new applications in November 2024 and Phase 4 is its final phase. We're seeing recurring patterns separate winning Trust applications from losing ones — and the patterns have less to do with technology choice than with how the application is framed and what scope it covers. Here's the strategy that consistently wins.

The cost-per-tonne metric is everything

Phase 4 scoring is dominated by cost-per-tonne CO₂ saved over project lifetime, with a soft cap that's landed around £350/tonne in current windows. Solar-only NHS Trust applications struggle here because hospital electricity demand is partly already-decarbonised on-grid — solar offsets grid imports that average ~0.18 kg CO₂/kWh, producing cost-per-tonne in the £400–£500 range that doesn't clear the soft cap.

Bundled applications win. Heat pump installations replace direct gas heating (CO₂ factor ~0.21 kg/kWh) where carbon savings per pound spent are stronger. Solar combined with heat pumps and fabric efficiency typically scores £200–£320/tonne — comfortably below the soft cap.

The multi-site portfolio approach

NHS Trusts have major advantages from portfolio-level bidding that single-site applicants don't. Combine multiple estate sites in a single bid:

  • Acute hospital — large continuous-load site, strong solar self-consumption, partial heat-pump opportunity
  • Community hospitals — typically 2–6 per Trust, smaller scale, heat-pump opportunity often substantial (gas-heated buildings)
  • Ambulance HQ + ambulance stations — operational estate with day-and-night demand profiles
  • Mental health units — variable demand, strong fabric and BMS opportunities
  • Corporate offices and admin sites — daytime demand, easier solar deployment

Why portfolio outperforms: cost-per-tonne metric averages across the bundle. Sites with strong economics (community hospitals with heat-pump bundles) pull down the average. Single-site applications are evaluated alone; portfolio applications averaging across diverse sites typically score 30–50% better on the cost-per-tonne metric.

The bundled-package recipe

Winning Phase 4 NHS applications consistently combine four interventions:

  1. Air-source heat pumps on community hospital and gas-heated estate

    Highest cost-per-tonne benefit. Replaces gas heating with electricity-driven heat. Combined with solar PV creates substantial Scope 2 reduction.

  2. Solar PV across acute hospital and rooftop-suitable estate

    Provides electricity for heat pumps and broader site demand. Strong continuous self-consumption on 24/7 hospital sites.

  3. LED relighting across the entire estate

    Smaller individual saving but very low cost-per-tonne. Lifts the bundled metric.

  4. Building management system upgrades

    Optimises heat pump and solar performance. Provides demand-management capability for winter peak periods.

Application timeline and resource intensity

Trust-level Phase 4 applications are substantial undertakings:

  • Pre-application work: 6–10 weeks for site surveys, demand modelling, and intervention specification across multi-site portfolio. Typically requires both internal Trust energy team and external technical adviser.
  • Application drafting: 4–6 weeks for full application document including technical specification, financial modelling, carbon savings calculations, procurement strategy, and 25-year operational plan. Trust finance team plus external Salix-application specialist.
  • Salix application window: Typically 8 weeks open. Application must be submitted within window.
  • Assessment timeline: 12–16 weeks from application close to award notification.
  • Delivery timeline: 18–24 months from award to commissioning.

Total Trust resource: 200–400 hours of internal time across application + delivery; £25k–£60k of external advisor cost. Successful applications typically deliver 50–100× this in grant value, but the application is genuine work.

What's causing rejections in 2026

  • Single-site solar-only applications. Cost-per-tonne too high; consistent decline.
  • Insufficient demand modelling. Applications relying on annual consumption rather than half-hourly modelling fail at first-pass review.
  • Missing operational plan. Phase 4 weights post-installation operational support more than Phase 3. Applications without 25-year O&M plan score lower.
  • Underestimated delivery resource. Trust applications without named delivery resource and credible engagement-to-completion plan being deferred for re-application with stronger delivery framework.

For Trusts without applied PSDS Phase 3 experience

Trusts that haven't previously applied to PSDS face a learning curve. Recommended approach:

  • Engage external technical adviser with Phase 3 application experience early. The application requires specialist methodology beyond standard Trust energy management.
  • Cross-reference with peer Trusts. Several Trusts publish their PSDS application strategies through CIBSE NHS sustainability events and HFM journal articles — useful template.
  • Engage Salix's pre-application support service. Salix provides indicative scoring against draft applications before formal submission. Useful pre-flight check.

Frequently asked questions

What is the Public Sector Decarbonisation Scheme Phase 4 and when does it open?
PSDS Phase 4 is the continuation of the DESNZ grant programme funding heat decarbonisation and energy efficiency in public sector buildings. Phase 3c closed in early 2025; Phase 4 is expected to open for expressions of interest in late 2025 or early 2026, with full applications in mid-2026. NHS Trusts, Local Authorities, blue-light services, and schools are the primary eligible body types. Solar PV is eligible where it supports a heat decarbonisation package or reduces grid dependency for electric heat pumps.
How do NHS Trusts calculate cost-per-tonne of CO2 for a PSDS application?
DESNZ assesses PSDS bids primarily on £/tCO2 abated over the project lifetime. For solar PV, calculate lifetime generation (25 years × annual yield in kWh), apply the grid carbon intensity factor (currently ~0.233 kgCO2/kWh), then divide total project cost by total tonnes abated. A 200kWp system generating 180,000 kWh/year abates around 1,050 tCO2 over 25 years. At £200,000 installed cost, that is £190/tCO2 — competitive if the portfolio blend brings the average below DESNZ's informal £250/tCO2 threshold.
Should NHS Trusts bundle multiple sites in a single PSDS application?
Yes, bundling almost always improves success rates. Bundled applications achieve lower average £/tCO2 by including high-impact, low-cost sites alongside more complex ones, while single-site applications on difficult buildings often exceed cost-per-tonne thresholds. Bundles also demonstrate estate-level strategic intent, which assessors value. The practical challenge is procurement: bundled projects need a single contractor or a pre-agreed consortium to deliver across multiple sites simultaneously.
What is the typical grant size for an NHS Trust solar project under PSDS?
NHS Trust PSDS grants for solar-inclusive projects have ranged from £500k to over £10m depending on scope. Pure solar-only projects rarely secure the largest grants — the highest grant values go to integrated heat-and-power packages where solar reduces grid load for heat pumps. A 500kWp solar portfolio across five Trust sites might attract a £600k–£900k grant (covering 40–60% of capital cost) when bundled with LED and controls upgrades that improve the overall cost-per-tonne metric.

Get your written finance comparison

Tell us about your project and we'll reply within 1 working day with a written comparison: the two or three funding routes that fit your situation, indicative monthly costs for each, and the capital allowances you'd keep.

What we won't do: no marketing lists, no unsolicited calls, and we never pass your details to installers or lenders without your permission. We're an independent editorial advisory — not an installer, not a broker taking commissions.

We ask for these details because they decide which routes fit — company profile drives the credit view, project type drives the structure. See our privacy notice for how your details are handled.

Need this analysis applied to your specific project?

Send postcode, half-hourly data file, and accounting year-end. We come back inside five working days with the after-tax model across all relevant finance structures.

Request a finance review