Hybrid Power Plants (HPP), combining renewable generation units and new consumption patterns with Battery Energy Storage Systems (BESS), are becoming a cornerstone of the European power system transformation. Baring a broad and highly dynamic flexibility, BESS play a critical role in providing strongly needed system services to enable higher shares of inverter-based resources both on generation and on consumption side while supporting system stability. Reflecting this evolving role, the revisions of the European Network Codes Requirements for Generators (RfG) and Demand Connection Code (DCC) have been intended to explicitly address hybrid assets and energy storage systems as system-relevant grid users. This is an important extension as the initial Network Codes as of 2016 have not addressed storage systems at all, except for pump hydro. The revisions had been elaborated based on a European wide stakeholder involvement conducted by ACER already back in 2022/2023. A final draft had been handed over to the European Commission to conclude the legislative process, which is, however, pending since then. Recently, the Commission, has announced that the codes shall be published in 2026, hence, ending a long period of waiting for an entire industry.

This contribution discusses the anticipated technical requirements for BESS within Hybrid Power Plants as they emerge from the revised RfG and DCC drafts. Key focus areas include requirements related to frequency and voltage support, fault ride-through capability, dynamic reactive power provision, active power control, as well as observability, controllability, and communication at both plant level and point of connection.

A particular emphasis is placed on the dual nature of BESS, which can operate as both generation and demand, and the resulting implications for the applicability, interaction, and alignment of RfG and DCC provisions. The paper highlights those areas where the revisions aim at greater harmonisation of technical requirements across Europe, while also identifying aspects that are likely to remain subject to national implementation and interpretation.

In addition, the contribution addresses conformity assessment and compliance demonstration obligations under the European Network Codes. It outlines the expected requirements to provide technical documentation, simulation models, and test evidence to the responsible system operator, and discusses open questions regarding the scope of conformity assessment for hybrid configurations, including the allocation of compliance responsibilities between individual components and the hybrid plant as a whole.

Despite the technical clarity achieved in the draft Network Codes, the continued delay in their formal adoption and publication has created a prolonged regulatory limbo. For manufacturers, project developers, and system operators, this situation complicates grid connection agreements, conformity assessment strategies, and investment decisions, as projects must already be designed against requirements that are known in substance but not yet legally binding. This contribution therefore critically examines how the industry is navigating this transitional phase and which technical and procedural approaches may help bridge the gap between long-available drafts and their awaited implementation. A rough comparison with already existing technical provisions in national grid codes is demonstrated.