Photovoltaics, Storage, Direct Current, and Flexibility in Building Energy Systems: A Review of Technologies, Coordination, and Grid Interaction

Buildings are increasingly required to accommodate distributed renewable generation while providing flexible demand and supporting power system operation. However, the existing review literature remains fragmented across photovoltaic (PV) systems, energy storage, direct current (DC) distribution, building energy flexibility, and energy management research. This review uses photovoltaics, storage, direct current, and flexibility (PSDF) as a building-centered analytical framework for synthesizing international research conducted under diverse terminologies. Following a PRISMA-based screening process, the selected literature was analyzed through bibliometric and thematic synthesis. The literature is organized through a three-layer framework comprising component technologies, coordination mechanisms, and interaction/application pathways. The review shows that PV and conventional battery storage are comparatively mature at the building scale, whereas DC system standardization, protection, interoperable converters, and scalable flexible load integration remain important engineering barriers. Demand-side management, demand response, and energy management systems are identified as the coordination layer that converts physical flexibility into economic, operational, and grid-support services. At the application level, coordinated buildings can contribute to renewable self-consumption, peak management, voltage regulation, resilience, and community energy sharing, although reported quantitative benefits are strongly case-dependent. Future research should prioritize interoperable and safety-oriented DC architectures, uncertainty-aware and cyber-resilient coordination, life cycle and multi-objective assessments, occupant-centered flexibility, and validation from single-building demonstrations to building–community–grid applications. These findings position PSDF as an integrative framework for flexible and grid-interactive building energy systems rather than as a fixed combination of four technologies.