Slide 1: Additional Technical Requirements for Grid-Forming BESS and Large Inverter-Based Loads
Additional Technical Requirements for Grid- Forming Battery Energy Storage System and Large Inverter-Based Loads Connected to Elia Transmission system Updated slides after WG BU workshop 24 October 2025
Slide 2: Key Outcomes of Stakeholder Workshop on 24/10 and Elia Responses (1/2)
Key Outcomes of Stakeholder Workshop on 24/10 and Elia Responses (1/2) Stakeholders were broadly supportive of Elia’s approach to introduce interim requirements for GFM BESS & large inverter-based loads, recognizing the importance of maintaining system stability in a low-inertia context. However, se
Slide 3: Key Outcomes of Stakeholder Workshop on 24/10 and Elia Responses (2/2)
Key Outcomes of Stakeholder Workshop on 24/10 and Elia Responses (2/2) 3. System-need justification Participants requested a clearer rationale for why each capability is required and suggested market-based approaches for some services. Elia response: • Detailed system-need justifications were alread
Slide 4: Objective of this workshop
Objective of the workshop Objective of this workshop • Remind the context and present the fast-track approach principles, • Explain the technical background and motivation behind the GFM BESS and large transmission-connected inverter- based loads (LTCIBL) requirements, • Share our vision for their i
Slide 5: Workshop agenda
Workshop agenda 09:30 – 10:00 | Welcoming & Introduction 10:00 – 12:00 | Session 1: Proposal for Grid-Forming BESS Requirements 12:00 – 13:00 | Lunch Break 13:00 – 15:00 | Session 2: Proposal for Large Transmission-Connected Inverter-Based Loads Requirements 15:00 – 15:30 | Coffee & Soft Drinks Each
Slide 6: Context, motivation and scope
Context, motivation and scope 6
Slide 7: Why New Technical Requirements for GFM BESS and LTCIBL?
Why New Technical Requirements for GFM BESS and LTCIBL1? 1. Power System Evolution • Rapid integration of power electronics → more RES, flexibility, efficiency. • Reduced system strength & inertia → voltage control and frequency stability at risk. • Complex control dynamics → oscillations and smalle
Slide 8: Elia's Proposal for New Requirements
Elia’s Proposal for New Requirements 1. Target Assets o Grid-Forming (GFM) BESS o LTCIBL1 (e.g., P2G, data centers) 2. Objectives o Strengthen voltage and frequency withstand capabilities. o Capability inertia and system support from BESS and large demand units. o Ensure robust integration ahead of
Slide 9: Identifying grid users for new technical requirements
Identifying grid users for new technical requirements The grid users for implementing new technical requirements: • Type D BESS connected to ELIA transmission system* • Aggregated inverter-based demand units > 75 MW connected to ELIA transmission system *ELIA transmission system is voltage above 70k
Slide 10: Scope of application (updated)
Scope of application (updated) The requirements shall only apply to new sub-category of units, if at the EIF of the RD amending the FTR and imposing the new requirements the units: • are the subject of an application for connection, • have been the subject of a connection contract, while the owner o
Slide 11: Principles for fast-track implementation
Principles for fast-track implementation 11
Slide 12: Main principles for fast-track implementation: System security
Main principles for fast-track implementation System security: Purpose: To ensure the stability and resilience of the Belgian power system under normal and disturbed conditions. Explanations: • Type D BESS units and LTCIBL connected at transmission system are directly coupled to the transmission bac
Slide 13: Main principles for fast-track implementation: Proportionality
Main principles for fast-track implementation Proportionality Purpose: To ensure that the additional responsibilities imposed on grid users are proportionate to their impact on and benefit to system operation Explanations: • Implementing the requested capability for both Type D BESS units and LTCIBL
Slide 14: Main principles: Non-discrimination and technical maturity level
Main principles for fast-track implementation Non-discrimination Purpose: To ensure that requirements are applied consistently and fairly, without undue disadvantage to specific categories of users or technologies. Explanations: • Across Europe, several TSOs (e.g., Energinet, RTE) apply or plan to a
Slide 15: Overview of new technical requirements for GFM BESS
Overview of new technical requirements for GFM BESS
Slide 16: Definition of a converter with Grid Forming capability
Definition of a converter with “Grid Forming” capability – A Grid Forming converter is a converter whose behavior can be approximated by a voltage source behind a series impedance [ENTSO-e]. The voltage source behavior means: • No dependency on an external voltage reference • Capability to support t
Slide 17: Overview of new technical requirements for GFM BESS
Overview of new technical requirements for GFM BESS Elia additional requirements for GFM BESS Phase angle jump capability (voltage source behavior ) Voltage magnitude step capability (voltage source behavior) Phase angle jump withstand capability (withstand capability) High voltage ride-through capa
Slide 18: Detail of GFM BESS technical requirements
Detail of GFM BESS technical requirements 18
Slide 19: Overview of technical requirements for GFM BESS
Overview of technical requirements for GFM BESS – Voltage source behavior o Phase angle jump capability o Voltage magnitude step capability – Withstand capability o Voltage phase angle withstand capability o High voltage ride through capability – Inertial response capability – Black-start with soft
Slide 20: Phase angle jump capability
Phase angle jump capability (part of voltage source behavior) What is a phase jump: A sudden step change in the voltage phase angle at the point of Other TSOs practice connection due to grid reconfigurations, faults cleared, sudden loss of large generation, system split. TSO/entity Response Currentl
Slide 21: Overview of technical requirements for GFM BESS
Overview of technical requirements for GFM BESS – Voltage source behavior o Phase angle jump capability o Voltage magnitude step capability – Withstand capability o Voltage phase angle withstand capability o High voltage ride through capability – Inertial response capability – Black-start with soft
Slide 22: Voltage magnitude step capability
Voltage magnitude step capability (part of voltage source behavior) What is it about: A sudden step change in the voltage magnitude at the point of connection Other TSOs practice due to grid faults, sudden change of power flow, fault elimination, …. TSO/entity Response Currently in Elia grid: • The
Slide 23: Overview of technical requirements for GFM BESS
Overview of technical requirements for GFM BESS – Voltage source behavior o Phase angle jump capability o Voltage magnitude step capability – Withstand capability o Voltage phase angle withstand capability o High voltage ride through capability – Inertial response capability – Black-start with soft
Slide 24: Voltage phase angle jump withstand capability
Voltage phase angle jump withstand capability What is it about: A sudden step change in the voltage phase angle at the point of connection Other TSOs practice due to grid reconfigurations, faults cleared, sudden loss of large generation, system split. TSO/entity Phase angle Currently in Elia grid: E
Slide 25: Overview of technical requirements for GFM BESS
Overview of technical requirements for GFM BESS – Voltage source behavior o Phase angle jump capability o Voltage magnitude step capability – Withstand capability o Voltage phase angle withstand capability o High voltage ride through capability – Inertial response capability – Black-start with soft
Slide 26: High voltage ride through (HVRT) capability
High voltage ride through (HVRT) capability What is it about: When the grid voltage rises above nominal (e.g., fault clearance or switching Other TSOs practice surge), BESS must tolerate and stay connected during temporary over voltages. TSO/entity Response Currently in Elia grid: • For BESS units,
Slide 27: Overview of technical requirements for GFM BESS
Overview of technical requirements for GFM BESS – Voltage source behavior o Phase angle jump capability o Voltage magnitude step capability – Withstand capability o Voltage phase angle withstand capability o High voltage ride through capability – Inertial response capability – Black-start with soft
Slide 28: Inertial response capability (contribution to synthetic inertia)
Inertial response capability (contribution to synthetic inertia) What is Synthetic inertia? It refers to the ability of non-synchronous generators to emulate the inertial response of synchronous machines during frequency disturbances in the power grid. Currently in Elia grid: Other TSOs practice • T
Slide 29: Overview of technical requirements for GFM BESS
Overview of technical requirements for GFM BESS – Voltage source behavior o Phase angle jump capability o Voltage magnitude step capability – Withstand capability o Voltage phase angle withstand capability o High voltage ride through capability – Inertial response capability – Black-start with soft
Slide 30: Black start capability with soft energization
Black start capability with soft energization Back start: the capability to re-energize part of a transmission system without any electrical energy Other TSOs practice supply external to the BS source, following a system shutdown (a high impact, low probability event). TSO Response Soft energization
Slide 31: References for GFM BESS requirements
References for GFM BESS requirements – ACER recommendation for the RfG 2.0 ACER_Recommendation_03-2023_Annex_1_NC_RfG_clean.pdf – ENTSO-E GFM report phase 2 Grid forming capability of power park modules – Germany: FNN Hinweis Netzbildende Eigenschaften V2.0 – Denmark: Towards a stable and sustainabl
Slide 32: Overview of new technical requirements for LTCIBLs
Overview of new technical requirements for Large Transmission-Connected Inverter-based Loads (LTCIBLs)
Slide 33: Scope of application (1/2)
Scope of application (1/2) Demand units with the largest grid impact are prioritized to maintain proportionality The fast-track connection requirements shall apply to: New transmission-connected inverter-based demand units with an aggregated peak load above 75 MW Element Definition Justification Tra
Slide 34: Scope of application (2/2)
Scope of application (2/2) Demand units: application to inverter-connected loads and critical auxiliaries A demand unit is defined as: an indivisible set of installations containing equipment which can be actively controlled by a demand facility owner, either individually or commonly as part of dema
Slide 35: Overview of new technical requirements for LTC IBLs
Overview of new technical requirements for LTC IBLs Elia additional requirements for LTC IBLs Frequency withstand capability RoCoF withstand capability Voltage phase angle jump withstand capability Behaviour after faults High-Voltage Ride-Through (HVRT) No contribution to sub-synchronous oscillation
Slide 36: Detail of LTCIBLs technical requirements
Detail of LTCIBLs technical requirements
Slide 37: Enhanced frequency and RoCoF withstand capability
Identical to requirement from Enhanced frequency and RoCoF withstand capability NC DC 2.0 draft (for P2G) Proposal Frequency range Duration Elia requires LTCIBLs to be capable of remaining connected for: 47.5 Hz – 48.5 Hz 30 minutes • Over-frequencies up to 52.5 Hz during 10 seconds 48.5 Hz – 49.0 H
Slide 38: Behaviour after faults: post-fault active power recovery (1/2)
NC DC 2.0 Art. XX(6) FRT: exhaustive Behaviour after faults: post-fault active power recovery PFAPR: non-exhaustive (PFAPR) (1/2) Relevance for the Belgian/European system • Power Generating Modules (and storage) are required to remain connected during voltage dips resulting from grid faults, and re
Slide 39: Behaviour after faults: post-fault active power recovery (2/2)
NC DC 2.0 Art. XX(6) Behaviour after faults: post-fault active power recovery FRT: exhaustive (PFAPR) (2/2) PFAPR: non-exhaustive Proposal • Fault Ride-Through capability per se is not mandatory : what matters is that the active power is recovered as fast as technically possible. • At this stage, no
Slide 40: High-Voltage Ride-Through (HVRT)
Identical to requirement from NC High-Voltage Ride-Through (HVRT) DC 2.0, Art. XX(7) for P2G Proposal • The LTC IBL shall remain connected and maintain stable operation as long as the voltage at the PoC remains within the voltage profile as displayed in the figure. In case of unbalanced fault, the v
Slide 41: Voltage phase angle jump withstand capability
Not in NC DC 2.0, but planned by Voltage phase angle jump withstand capability multiple European TSOs Proposal • LTCIBLs within the scope shall be capable of remaining connected to the grid during voltage angle shifts up to 45 degrees, measured at the connection point, for the phase seeing the large
Slide 42: Inverter-based loads should not be a source of sub-synchronous oscillations
Inverter-based loads should not be a source of NC DC 2.0, Art. 17: non-exhaustive sub-synchronous oscillations Oscillations • Systems with a lack of sufficient damping torque can experience oscillations resulting from different sources • Inter-plant oscillations: in the same plant, units oscillate a
Slide 43: Limited Frequency Sensitive Mode – Underfrequency for Consumption (LFSM-UC)
Identical to requirement from NC Limited Frequency Sensitive Mode – Underfrequency DC 2.0, Art. XX(3) for P2G for Consumption (LFSM-UC) Proposal Within the limits of the industrial process, the LTC IBLs shall be able to reduce its consumption progressively in function of frequency decreasing. • This
Slide 44: Data and modelling requirements for LTC IBLs
Data and modelling requirements for LTC IBLs
Slide 45: Data and modelling requirements for LTC IBLs
Data and modelling requirements for LTC IBLs Proposal All demand units with an aggregated capacity equal to or above 75 MW shall provide detailed vendor models of their power-electronic connected equipment and information about other loads. Relevance for the Belgian/European system Elia requires an
Slide 46: References for inverter-based loads requirements
References for inverter-based loads requirements – ACER recommendation for the NC DC 2.0: https://acer.europa.eu/sites/default/files/documents/Recommendations_annex/ACER_Recommendation_03- 2023_Annex_2_NC_DC_clean.pdf – Germany: Requirements for the connection of electrolyser facilities – Denmark: D
Slide 47: Next steps
Sia Next steps
Slide 48: Roadmap for GFM BESS & Load Capability Requirements Implementation
Roadmap for GFM BESS & Load Capability Requirements Implementation Preparing draft proposal for public consultation Public consultation Nov - Dec Discussion with FOD & CREG 20 Nov Discussion with FOD Discussion with FORBEG Sep 29 5 Nov Discussion with FOD & CREG 27 Nov Discussion with Synergrid High
Slide 49: Executive Summary
€ia Executive Summary
Slide 50: Executive summary of the workshop
Executive summary of the workshop The rapid increase in inverter-based assets such as BESS, P2G, and data centers is impacting system strength and inertia; with EU codes (RfG 2.0 / DCC 2.0) still under development, interim national rules are required to ensure system stability and preparedness for f
Slide 51: Thank you for your attention!
Thank you for your attention! If you have questions regarding Grid-Forming BESS, feel free to contact: => Nakisa.Farrokhseresht@eliagrid-int.com For inquiries related to LTC Inverter-Based Loads, please reach out to: => Martijn.Backer@eliagrid-int.com