The PORTAL GREEN project, carried out from 1 January 2018 to 31 December 2020, produced a comprehensive, unified guide for the design, approval, construction and operation of Power‑to‑Gas (PtG) plants. The guide integrates technical and regulatory requirements into the existing DVGW rule set, thereby providing a single reference for operators and manufacturers. A key technical outcome was the development of a reference plant that illustrates the layout, system boundaries and component specifications for a typical industrial‑scale PtG installation. This reference plant serves as a benchmark for performance assessment and for the identification of critical safety and environmental parameters. The project also produced a detailed questionnaire for plant operators, which captures operational data and facilitates the evaluation of plant performance against regulatory thresholds. In addition, the guide defines specific requirements for PtG plants that incorporate power injection into the grid, addressing the unique challenges of bidirectional flow and grid stability. The technical documentation includes a systematic classification of safety inspections, monitoring obligations and licensing conditions in accordance with German occupational safety regulations (BetrSichV) and the Energy Industry Act (EnWG). By consolidating these requirements, the guide reduces the time and cost associated with compliance checks and accelerates the approval process for new PtG projects. The regulatory component of the guide was developed through close collaboration with authorities, resulting in a clear outline of the environmental assessment (UVP) procedure, including the necessary documentation, deadlines, and the integration of natural protection measures. The guide specifies the sequence of environmental impact studies, the required data on surrounding habitats, and the mitigation measures for potential adverse effects, thereby ensuring that PtG projects meet the stringent environmental standards set by the German Environmental Impact Assessment Act (UVPG). The project’s collaborative framework involved five partners: the Gesellschaft für Anlagen‑ und Reaktorsicherheit (GRS), the Bergische Universität Wuppertal (BUW), the Deutsche Verein des Gas‑ und Wasserfaches (DVGW), DBI Gas‑ und Umwelttechnik GmbH, and Uniper Energy Storage. GRS coordinated the consortium, organized workshops, and led the development of the reference plant and specific industrial requirements. DBI was responsible for drafting the regulatory guide, gathering feedback from authorities, and creating the operator questionnaire and system‑boundary overview. DVGW focused on the technical guide and its integration into the DVGW rule set, while BUW contributed expertise on electrical components and the regulatory aspects of power‑injection PtG systems. Uniper Energy Storage participated in the consortium, providing industry perspective and contributing to the practical relevance of the guide. Each partner submitted independent funding applications, and the consortium’s cooperation agreement governed confidentiality and data sharing. The resulting guide, now part of the DVGW rule set, offers a structured, evidence‑based framework that streamlines the approval process, mitigates economic risk, and supports the competitive deployment of PtG technology in Germany.