The ongoing energy transition towards high shares of converter-based generation and storage calls for a fundamental shift in power system stability management. Traditional synchronous plants historically provided essential grid-forming functions, such as voltage and frequency stabilization and short-circuit current contribution. With their phase-locked, grid-following behavior, conventional inverter-based systems cannot inherently deliver these system services, creating challenges for a stable, low-inertia network. To address these challenges, German stakeholders have recently advanced two key regulatory frameworks for grid-forming (netzbildende) converters and battery storage integration.

The VDE-FNN “Technical Requirements for Grid-Forming Properties including the Provision of Instantaneous Reserve” provides the first comprehensive national guideline specifying both functional and demonstrative requirements for grid-forming units across voltage levels as a prerequisite to contribute to an upcoming market of momentary reserve power. This guideline defines technical capabilities such as controlled voltage source behavior, provision of instantaneous reserve, and system support functionalities that mirror the stability contributions of synchronous machines. Importantly, it also outlines measurement-based and simulation-based test procedures to support certification and market participation, thereby aligning with the national System Stability Roadmap.

Complementing this, the 4-TSO paper on requirements for grid-forming converters, developed by Germany’s four transmission system operators (ÜNB), articulates a harmonized set of basic and optional grid-forming capabilities. These capabilities, rooted in international studies such as ENTSO-E’s HPoPEIPS report, are classified into mandatory functions essential for safe grid operation and additional features that may be required depending on local grid conditions. It also provides a link to the upcoming unified technical basis in terms of the expected revisions of European network codes and, hence, respective national technical application rules in other European Member States.

This contribution presents an integrated overview of both the technical requirements and the evidence-based compliance mechanisms emerging in Germany for grid-forming inverters and battery storage systems. It examines the state of certification practices according to the FNN regulation for the eligibility of such installations to participate in the newly establised instantanious reserve power market as well as the required simulation studies to proof conformity to the TSO requirements. It discusses practical challenges in demonstrating compliance through tests and modeling, and highlights early certification efforts in the industry. By synthesizing recent regulatory progress and implementation status, the paper elucidates how these frameworks support the broader objective of enabling secure and resilient power system operation with high inverter-based generation.