BESS Harmignies

Introduction

Energy Solutions Group (ESG) has developed one of Belgium’s largest Battery Energy Storage System (BESS) projects in Harmignies. The 76 MW / 300 MWh installation, built around 82 Tesla Megapack 2XL units and connected directly to the Elia 150 kV grid, will play a major role in providing flexibility, balancing services, and supporting renewable integration into the Belgian electricity network.

Enersynt was appointed as Owner’s Engineer for the electrical systems, supporting ESG through all project phases, from early design review to commissioning and grid compliance.

Project Background

As Belgium accelerates its energy transition, large-scale storage assets like the BESS in Harmignies are essential for grid stability and accommodating growing volumes of renewable energy. The system enables fast-acting services to the transmission system operator Elia, including frequency regulation, congestion management, and peak load support.

The project required the integration of multiple suppliers and contractors, including SPIE as EPC contractor and Tesla as battery supplier, along with extensive interfacing with Elia for the grid connection, control & protection systems, and grid compliance validation.

After nearly two years of design, construction, and testing, the project successfully passed hot commissioning and reached its official opening in September 2025.

Role of Enersynt

As Owner’s Engineer, Enersynt acted as ESG’s technical representative throughout the project, ensuring quality, safety, and compliance while facilitating clear technical interfacing between all parties.

Engineering Review and Technical Follow-up

• Follow-up of the basic and detailed engineering of the plant.
• Review of electrical designs, HV systems, protection philosophy, and integration between Tesla, SPIE and Elia requirements.
• Continuous feedback to ensure the proposed solutions remained robust and aligned with project expectations.

Power System Studies

• Carried out power system calculations, including load flow, short-circuit, cable ampacity and RAMS-related analyses, to validate key design assumptions and support progress when needed.
• These calculations complemented the EPC’s engineering work and provided ESG with an additional layer of assurance regarding the system’s performance.

Factory Acceptance & On-Site Testing

• Witnessing of key factory tests, including the main power transformer FAT at the manufacturer’s facilities.
• Follow-up of SCADA and automation systems integration, verifying correct operation of control, protection, and communication functions.
• Support during on-site testing, including Elia interface tests, verification of protection schemes, energisation activities, and hot commissioning of the grid connection and battery systems.
• Participation in performance validation to confirm that the operational behaviour matched contractual and technical expectations.

Grid Compliance Support

• Review of the grid compliance documentation prepared for Elia, ensuring technical consistency and clarity.
• Support to ESG in technical discussions with Elia, helping align expectations on grid code requirements, control behaviour, and commissioning steps.
• Ensured that all electrical and control interfaces between the BESS and the 150 kV grid were correctly implemented and validated during site testing.

Conclusion

The Harmignies BESS is a milestone for Belgium’s evolving energy system, delivering large-scale flexibility and enabling greater penetration of renewable power. As Owner’s Engineer, Enersynt ensured technical quality, regulatory alignment, and secure integration of the asset into the 150 kV grid.

We are proud to have supported Energy Solutions Group throughout this flagship project and to have contributed to the successful delivery and commissioning of one of Belgium’s most significant storage installations to date.

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