In 2021 and 2022 the Clean energy for EU islands secretariat (the secretariat) conducted a study on the regulatory barriers affecting the clean energy transition of islands. This provided significant insights into the operation of the islands’ electricity systems and formulated recommendations to overcome existing challenges. Grid constraints and the lack of security of supply were identified as two of the key barriers to the decarbonisation of EU islands’ energy systems. Building on that study, the secretariat has been focusing its recent work on the connection policies of renewable energy power plants and the management of energy systems under conditions of asynchronous generation, specifically in non-interconnected islands. The goal of the study is to develop key recommendations and guidance to support the integration of increased renewable energy production and storage while ensuring system stability and security of supply. The study deepens the understanding of the existing grid regulatory and operating constraints in 10 representative islands and groups of islands.