450 kW Solar PV on a University HPC Research Computing Facility — Cambridge

Project background

Cambridge’s role in UK high-performance computing is substantial and growing. The University of Cambridge operates several research computing facilities including the University High Performance Computing Service, and Cambridge is home to the Hartree Centre’s national HPC infrastructure (operated from Daresbury but with Cambridge-based collaborative facilities). The Alan Turing Institute, Arm Research, and Microsoft Research all maintain research computing capacity in or adjacent to the city.

This project involved a university-operated HPC research computing facility — a dedicated building providing high-performance computing infrastructure for research groups across the university and its affiliated institutes. The facility receives UKRI (UK Research and Innovation) funding and is subject to sustainability reporting requirements under UKRI’s research environment assessment framework.

The stakeholder environment for a university computing facility differs from commercial data centre projects in several important ways: governance involves multiple committees and sign-off processes, procurement must comply with OJEU/Find a Tender Service thresholds, and the installation must be coordinated with the academic calendar to minimise impact on research computing availability during term time.

The facility

The building is a purpose-built research computing facility constructed in 2017, approximately 3,800 sqm gross floor area, operating at Tier III standard. IT load averages 1.4 MW across the year, peaking to 1.8 MW during intensive computing runs (typically research simulation periods during term time). The facility runs 24/7, 365 days a year — research computing obligations do not follow a 9-to-5 schedule.

The roof is a flat, high-performance single-ply membrane (Sarnafil S327) installed during construction and in excellent condition at time of survey. Available solar PV area is 3,200 sqm — one of the more generous roof-to-building ratios in our portfolio, as the building was designed without rooftop plant beyond a small HVAC unit cluster.

The Cambridge location receives approximately 1,600 hours of sunshine annually — among the highest for any major UK city, driven by Cambridge’s position in the drier, sunnier eastern England climate zone. This is the highest irradiance site in our data centre portfolio and delivers the best annual generation per kW of installed capacity.

Procurement and governance

University procurement for a project of this value (>£524k) required compliance with the Find a Tender Service (FTS) regulations governing public sector contracts. The university’s estates procurement team ran a compliant tender process over a 12-week period. We were appointed on the basis of a qualitative submission addressing technical methodology and data centre sector experience, as well as price — it was explicitly not awarded on lowest price alone.

The internal approval process involved the university’s Sustainability Strategy Committee (which oversees net zero commitments), the IT Services Computing Management Board (which governs the HPC facility), and the Estates Division Capital Projects Committee. This is a longer and more structured approval process than commercial data centre projects, and the 12 months from initial engagement to site mobilisation reflects that governance reality.

Contractors working on the university estate must comply with the university’s Contractor Health & Safety and Environmental Policy, including the requirement for CSCS card holders for all on-site construction activities and mandatory induction for every person entering site.

System design

The 450 kW array uses 893 REC Group Alpha 505 Aa half-cut heterojunction (HJT) modules. HJT modules were selected for this project because of their superior low-irradiance performance — Cambridge receives more diffuse light days than the Thames Valley, and HJT technology produces proportionally more energy per kW in overcast conditions relative to standard PERC. The temperature coefficient of HJT is also lower (−0.24%/°C vs −0.34%/°C for PERC), which is a minor but real benefit in UK summers.

Mounting is via a SunRoof ballasted racking system in portrait orientation at 12° pitch, configured with East-West row spacing to avoid mutual shading on the low-pitch flat roof. Nine SolarEdge SE50K commercial string inverters (50 kW each) with individual panel-level SolarEdge S-Series optimisers — specified because a small area of roof runs under partial shade from an adjacent building extension for approximately 90 minutes in the afternoon during the winter months. The optimisers ensure that shaded panels do not reduce the output of the unshaded strings.

Eastern Power Networks (now UK Power Networks — Cambridge is served by the UKPN Eastern region) G99 Protection Relay application was submitted in March 2025 and approved in 44 working days.

System summary:

• Array capacity: 450 kW (893 × 505 Wp REC Alpha HJT)
• Inverters: 9 × SolarEdge SE50K + S-Series optimisers (partial shade mitigation)
• Mounting: SunRoof ballasted, 12° East-West portrait
• Grid connection: UKPN Eastern G99 (44 working days)
• Monitoring: SolarEdge monitoring + API output to university energy dashboard
• Procurement: FTS-compliant tender process

Installation scheduling — long vacation commissioning

The most important operational constraint on this project was the computing availability commitment: the facility provides research computing services to over 40 active research groups, and a planned outage during term time would directly affect grant-funded research projects, some with submission deadlines for results.

The university’s IT Services team proposed a commissioning window during the Cambridge Long Vacation (July–September), during which overall research computing demand drops to approximately 30% of peak. The project was planned so that the physical array installation (non-electrical — low risk to computing operations) could take place during any part of the year, with the electrical commissioning — the single activity requiring a planned power event — reserved for the Long Vacation window.

The physical installation (893 modules, mounting, and DC cabling) was completed in April 2025 during a 14-day period with no electrical works near live systems. The electrical commissioning — AC connection at the LV board, Protection Relay commissioning, and system energisation — was completed in 4 days during the Long Vacation in July 2025.

Installation timeline:

• February 2025: Site mobilisation, roofing contractor preparation
• April 2025: Module and racking installation (14 days)
• May–June 2025: G99 Protection Relay commissioning preparation
• July 2025: AC connection and system energisation (4 days, Long Vacation window)
• July 2025: System handover and monitoring verification

Results and Cambridge irradiance performance

Cambridge’s 1,600 hours of annual sunshine delivers the best generation yield per kW of any project in our data centre portfolio:

• Annual generation (modelled P50): 418,500 kWh (930 kWh/kW — highest yield per kW in portfolio)
• Self-consumption ratio: 97.4% (minor export on low-demand research computing periods)
• Annual electricity cost saving (year 1): £92,000 at 22p/kWh
• CO₂ avoided: 58.6 tonnes CO₂e
• Capital cost: £524,000 (ex-VAT)
• Full Expensing tax relief: Note — university is exempt from corporation tax; capital allowances claimed via the university’s HMRC-registered trading subsidiary
• Simple payback (pre-tax): 5.7 years
• Project IRR (25-year DCF): 17%

UKRI sustainability reporting contribution

The UKRI research environment assessment framework — used in REF (Research Excellence Framework) submissions — includes sustainability criteria for research infrastructure. On-site renewable energy generation backed by MCS certification and REGO issuance is directly citable in REF environment statements as a contribution to the university’s institutional net zero pathway.

The 450 kW system, generating 418,500 kWh annually, provides approximately 29% of the HPC facility’s electricity consumption from zero-carbon on-site generation. This is cited in the university’s UKRI infrastructure reporting as a verified sustainability improvement to the research computing estate.

Reference availability

DC-CAM-004 is available as a reference for university and public sector research computing facilities, UKPN Eastern grid connection, Cambridge location, HJT technology selection, and FTS-compliant procurement. Reference calls arranged under NDA.