A comprehensive review of sustainable energy systems in the context of the German energy transition—part 2: renewable energy and storage technologies

As a continuation of part 1, which examined the development status and system foundations of sustainable energy systems (SES) in the context of German energy transition, this paper provides a comprehensive review of the core technologies enabling the development of SES. It covers recent advances in photovoltaic (PV), wind energy, geothermal energy, hydrogen, and energy storage. Key trends include the evolution of high-efficiency solar and wind technologies, intelligent control systems, sector coupling through hydrogen integration, and the diversification of electrochemical and mechanical storage solutions. Together, these innovations are fostering a more flexible, resilient, and low-carbon energy infrastructure. The review further highlights the importance of system-level integration by linking generation, conversion, and storage to address the intermittency of renewable energy and support long-term decarbonization goals.