Flexible solar-rechargeable energy system

Renewable energy generation/storage devices are promising solutions to address the current energy dilemma and global environmental degradation. Solar energy harvesting, especially photovoltaic (PV) systems, are attracting ever-increasing attention because of the abundance of renewable solar energy. However, the unstable and intermittent nature of sunshine requires the integration between PVs and energy storage systems, which has promoted the development of solar-rechargeable energy systems (SESs). Flexibility and portability are two key features that need to be considered when designing next-generation wearable and portable energy devices, especially for SESs. In this review, we firstly focus on the recent development of flexible SESs based on a range of PV systems aiming at revealing the limitations of state-of-the-art technologies. Then, we discuss the fundamental principles which determine the key performances of flexible SESs, such as energy efficiency, matching between PVs and ESSs, and flexibility issues. Finally, we provide the current challenges and outlook for the future of flexible SESs.