Solar power generation systems can be categorized into grid-connected and off-grid photovoltaic (PV) systems based on their connection to the power grid. Grid-connected PV systems refer to those that operate while connected to the power grid and are subject to grid dispatch-for example, centralized or distributed PV power plants. Off-grid PV systems, by contrast, operate independently of the power grid; examples include solar-powered streetlights and residential PV power systems for rural households.
Energy storage systems, which serve as an effective means of storing electrical energy, are classified into four categories: mechanical, battery, electromagnetic, and phase-change (thermal) energy storage. Among mechanical storage methods, pumped-hydro storage is already widely deployed, while flywheel energy storage-a newer mechanical approach-is currently in the research and demonstration phase. Electromagnetic energy storage encompasses technologies such as superconducting magnetic energy storage, supercapacitors, and high-energy-density capacitors. Thermal energy storage, which relies on the phase change of materials to store or release energy, is still in the laboratory research stage in China and has not yet seen practical application. Battery-based energy storage is a mature, widely adopted, and cost-effective technology. Off-grid PV systems utilizing lead-acid batteries have already reached the stage of commercial application. Furthermore, with the recent advancement of lithium-ion battery technology and the associated decline in costs, energy storage systems based on lithium-ion batteries have become a major focus of current research.