Design of a photovoltaic electric bike battery-sharing system in public transit stations

Small off-grid solar photovoltaic (PV) systems installed in small urban public space or on the roofs of urban facilities can allow PV power stored in shared EB (electric bike) batteries for using anytime and anywhere, and make almost no side effects on original functions of the system installation locations, which is an effective and economic approach for promoting solar energy utilization in cities. However, the constraints such as limited available roof in public transit stations and limitation of EB-battery charging current, will lower the utilization efficiency of PV charging power. To address this issue, this study proposed a method to design a PV EB battery-sharing (PVEBBS) system in public transit stations. From field measurements, it was found that the charging mode of “one PV array unit to one battery” is energy-efficient in PV power utilization and simple in system operation control. The proposed design method is to calculate an optimal size of PV array unit which can provide a better energy-saving effect both in PV power and AC auxiliary charging, under the condition to ensure one battery fully-charged within 6 h using PV power from one PV array unit on a day throughout a year (when solar radiation is insufficient on a day, the unfully-charged battery will be charged to a fully-charged state from AC power). A southern city (Nanning) of China was used as a case study object to demonstrate how to design a PVEBBS and determine an optimal size of PV array unit. Analysis results show that the optimal sizes of one PV array unit are between 2 m2 and 6 m2 for the six cites (Lhasa, Kunming, Beijing, Shanghai, Nanning, Chongqing) with different climates in China.