420 kW Solar PV on a Tier IV Hyperscale Facility — London Docklands, E14

Project background

The London Docklands campus cluster — Telehouse North, Telehouse North Two, and the Equinix LD facilities in E14 — represents the highest density of critical Tier III and Tier IV infrastructure in the UK. The site on this project is a fully redundant 2N Tier IV facility: every component of its power infrastructure is doubled, from the DNO import feeders through the UPS systems and distribution boards to the PDUs on every rack. At Tier IV, downtime is not a risk to be managed — it is an engineering condition to be eliminated.

The challenge for solar PV installation at Tier IV facilities is fundamentally different to Tier III. The AC connection of any new electrical system to a 2N facility must be accomplished without reducing the redundancy of the live power path. This means that the standard approach — connecting a new generation source to the main LV board during a planned window — is not available without significant risk analysis and, in most configurations, not acceptable at all.

Our work on this project centred on engineering an AC connection methodology that maintained full Tier IV power redundancy throughout commissioning.

The facility

The building is a seven-storey purpose-built hyperscale facility commissioned in 2008 and progressively expanded. Total IT load capacity is 18 MW across the building’s two independent power paths (9 MW per path), each supported by multiple diesel generator sets and a 2N UPS system. The facility holds Uptime Institute Tier IV Constructed certification.

Roof area available for solar was significantly constrained by rooftop cooling plant — the facility relies on direct expansion (DX) cooling plant which occupies substantial roof area. Our structural survey identified approximately 2,200 sqm of available solar PV area on the eastern and southern roof sections, capable of accommodating a 420 kW array.

Grid rates at this E14 location ran at approximately 26p/kWh on half-hourly metering — among the highest in our data centre portfolio, reflecting the premium-priced London distribution network.

The Tier IV connection challenge

In a 2N Tier IV facility, every circuit has a twin. Power path A feeds half the racks; power path B feeds the other half. Under normal operation, both paths are live simultaneously, providing instant failover if any single component fails. A Tier IV facility under design standards can tolerate any single failure, including complete loss of one power path, without any impact on load.

This architecture creates a genuine opportunity for solar AC connection: the connection can be made to power path B while power path A remains fully live under normal operating conditions. If any issue arises during connection work on path B, path A carries the entire facility load automatically — this is precisely what Tier IV redundancy exists to provide.

Our commissioning plan was reviewed and approved by the facility’s operations director and their Uptime Institute-accredited consultant before any on-site work began. The plan specified:

1. Solar array installation on roof (non-electrical — low risk)
2. DC wiring from array to inverters (low risk — no live AC involved)
3. Inverter installation adjacent to path B LV board (no energisation at this stage)
4. AC connection to path B LV board during planned maintenance window, with path A carrying 100% of IT load
5. Protection Relay commissioning with UKPN engineer in attendance
6. System energisation and monitoring verification
7. Documentation pack issued to operations team

At no point during electrical commissioning was Tier IV redundancy reduced below 2N.

System design

The 420 kW array uses 833 Canadian Solar HiKu7 CS7N-500MS half-cut PERC modules at 505 Wp each. Ballasted mounting on a single-ply PVC membrane roof using K2 System’s CrossFix profile — chosen for its extremely low roof penetration footprint (zero penetrations for the main array).

Five Fronius Symo GEN24 80.0 Plus inverters (80 kW each, with one spare capacity inverter as cold standby) connect to the dedicated solar generator sub-board on power path B. The path B LV board already carried the appropriate fault level capacity for a 420 kW addition — this was confirmed in our electrical design calculations reviewed by a chartered electrical engineer.

The UK Power Networks G99 Protection Relay — a Woodward BE1-50/51 — was installed in a dedicated cubicle adjacent to the path B incomer. The UKPN G99 formal application was submitted under the complex connection route (>50 kW) and approved in 38 working days.

An important nuance for this project: the UKPN grid substation serving this part of E14 operates under a constrained export regime. The system was configured with an export limitation relay set to zero export — all generation is consumed on-site. With 18 MW of continuous IT load, 420 kW of solar generates a self-consumption ratio of 100% under all operating conditions.

System summary:

• Array capacity: 420 kW (833 × 505 Wp Canadian Solar CS7N)
• Inverters: 5 × Fronius Symo GEN24 80.0 Plus
• Mounting: K2 CrossFix ballasted on PVC membrane
• Grid connection: UKPN G99 (38 working days), zero-export configuration
• Monitoring: Fronius Solar.web + EnergyTag GC API integration
• Tier IV validation: Uptime Institute-accredited review pre-commissioning

EnergyTag Granular Certificate integration

The operator’s sustainability team is targeting 24/7 carbon-free energy matching under the EnergyTag Granular Certificate (GC) framework. Unlike REGOs — which are annual certificates — EnergyTag GCs represent energy in one-hour intervals, enabling operators to demonstrate that their consumption was matched by zero-carbon generation at the specific hour it occurred.

The Fronius Solar.web monitoring platform has been configured to output half-hourly generation data to the EnergyTag certificate issuer via their API integration. This gives the operator hour-by-hour attribution of solar generation, directly feeding into their 24/7 CFE dashboard alongside the corporate wind PPA they hold for overnight hours.

This is the most granular sustainability accounting available to UK data centre operators — and it was available on this project because the monitoring hardware was specified to support it from the outset, not retrofitted.

Results

The system has been operational since commissioning (Spring 2025) and has completed its first full operational year:

• Annual generation (measured): 369,600 kWh (P50 modelled: 362,000 kWh — 2.1% above model)
• Self-consumption ratio: 100% (zero export events)
• Annual electricity cost saving (year 1): £96,096 at 26p/kWh
• CO₂ avoided: 51.7 tonnes CO₂e
• Capital cost: £516,000 (ex-VAT)
• Full Expensing tax relief (25% CT): £129,000 in year of expenditure
• Net capital cost after tax: £387,000
• Simple payback (pre-tax): 5.4 years
• Post-tax payback: 4.0 years
• Project IRR (25-year DCF): 19%

The 26p/kWh grid rate (among the highest in our DC portfolio) drives the above-average IRR despite the London Docklands location having slightly fewer solar hours than the Thames Valley.

Scope 2 and EnergyTag outcome

The operator holds 369,600 kWh of annual REGO issuance (market-based Scope 2 zero on the solar fraction). In parallel, EnergyTag GCs are issued hourly across the generation year — approximately 3,500 GC-hours in the first operational year. These feed directly into the operator’s 24/7 CFE dashboard, reducing the gap between their renewable energy volume and their hourly CFE achievement metric.

Reference availability

DC-LDN-002 is available as a reference for Tier IV facilities, London Docklands / E14 / UKPN grid, hyperscale scale (>10 MW IT load), and EnergyTag GC integration projects. Reference calls arranged under NDA — contact us with your project context.