Delivering 1.33 GWh of Annual Renewable Energy for a Major UK Distribution Centre

System Size	JA Solar 500 W	Solis 110K-5G	Annual Generation
1.824 MWp DC	3,648 Modules	12 Inverter	1,326 MWh/yr

Project Overview

This case study outlines our design and engineering of a 1.824 MWp DC/1.320 MW AC rooftop solar PV system installed on a large-scale distribution centre in Livingston, United Kingdom. 

The project involved 3,648 JA Solar 500 W modules mounted across approximately 81,814 m² of roof space, with 12 × Solis-110K-5G inverters providing AC conversion.

The system was designed using an East-West ballasted mounting arrangement at a 10° tilt angle. A configuration we chose specifically to maximise available roof area while working within the constraints of a busy operational facility.

The challenges

The site was drawing 6,663.5 MWh of grid electricity annually. Costly, carbon-heavy, and with over 81,000 m² of roof sitting largely unused. Skylights, rooftop plant, access routes, and live operational constraints meant our design had to work around the building.

• So the primary goals driving this were straightforward:
• Deliver a system built to comply fully with UK grid connection requirements.
• Reduce the site’s reliance on grid electricity and lower its carbon footprint.
• Make the best possible use of a large, underutilised rooftop.
• Integrate cleanly with the site’s existing electrical infrastructure.

The Solution 

1. Roof Structural & Construction Design

The roof layout had to accommodate a range of real-world constraints. Working around these, we developed a PV layout that maintained all required safety clearances while achieving strong module density:

• 1.2 m perimeter setbacks around all roof edges.
• 600 mm maintenance walkways between designated array sections.
• Clear access routes to rooftop equipment and services.
• Adequate clearances around skylights, vents, and other obstructions.

East-West Mounting Configuration

The ValkPro+ East-West ballasted mounting system with a 10° tilt angle was selected because it offered reduced row spacing and higher module density compared to a conventional south-facing arrangement. Both important factors given the scale of the roof.

Cable Routing & Roof Infrastructure

Routing 192 strings across such a large roof area was one of the more complex logistical challenges of the project. The solution was a dedicated rooftop cable tray network, designed to:

• Follow the defined maintenance pathways to keep routes accessible.
• Avoid roof obstructions and minimise unnecessary crossing points.
• Provide a structured, inspectable cable management system for the long term.

Eight cable trays (220 mm × 25 mm) were installed across the roof, each accommodating twelve strings. So 96 strings per roof section. 

All string connections used 6 mm² DC solar cables.

2. Electrical Design Engineering

DC Cable Routing

DC cable routes were optimised to reduce cable lengths and maintain clear access pathways across the roof. All string connections used 6 mm² DC solar cables, routed through the dedicated rooftop cable tray network for structured cable management and ease of future inspection.

Inverter & AC Collection Design

We adopted a centralised AC collection approach to aggregate the outputs of all 12 inverters before connection to the Main LV Switchboard. Conductor sizing was designed to balance efficiency, voltage drop, and practical installation constraints:

• Inverter AC feeders: 70 mm² conductors.
• Main AC collection circuits: 300 mm² conductors.
• Dedicated earthing conductors throughout the rooftop and electrical infrastructure.

Voltage Drop Optimisation

The cable routing strategy and conductor sizing were optimised to achieve an average voltage drop of approximately 1.8%. All circuits were comfortably below the recommended 3% maximum design limit.

Protection, Control & Monitoring

We implemented a G99 Protection Scheme to ensure compliance with UK grid requirements, for automatic disconnection in the event of abnormal grid conditions. An Energy Monitoring System was also incorporated for real-time performance tracking, fault detection, and operational reporting, giving the site team clear visibility of system performance from day one.

System results

System Summary

Key Engineering Achievements

• Delivered a high-density East-West rooftop layout across 81,814 m² while meeting all fire safety, maintenance, and operational requirements.
• Achieved an average voltage drop of ~1.8% across all circuits. Well within the 3% design limit.
• Modelled Performance Ratio of 86.72%, demonstrating a well-optimised system design.
• Integrated G99 protection and real-time energy monitoring for long-term operational reliability.
• Designed with scalability in mind to support future grid export functionality.

PVsyst Performance results

PVsyst modelling of the completed design produced the following annual performance projections:

Loss Analysis

• The modelled loss breakdown is as follows:
• Inverter Operational Loss: 2.3%
• Near Shading Loss: −0.9%
• Soiling Loss: −1.0%
• IAM Loss: −4.1%
• Irradiance Level Loss: 2.3%
• Temperature Loss: 0.6%
• Mismatch Loss: 1.1%
• DC Wiring Loss: 0.7%

This project allowed us to showcase our expertise in RF planning, municipal coordination, and performance optimization. Where urban density is the problem, smart network design makes it an opportunity. 

The Outcome

This rooftop solar system was designed to deliver meaningful energy savings while meeting all applicable UK standards and site requirements. The East-West mounting configuration was particularly effective at this scale, enabling strong roof utilisation without compromising access or safety.

The system is expected to generate approximately 1.33 GWh of renewable electricity annually, with a Performance Ratio exceeding 86%. It reflects the care taken throughout the design process in optimising cable routing, conductor sizing, and system configuration.

We’ve built this design also with scalability in mind. The infrastructure is in place to support future grid export functionality as the site’s requirements evolve.