Optimizing the photovoltaic-assisted electric bus network with rooftop energy supply

Abstract

As a clean and renewable resource, solar energy has demonstrated its potential to alleviate the energy vulnerability and grid strain for electric bus systems. In this study, we investigate the optimal design of an electric bus network in which rooftop solar panels are equipped to provide en-route photovoltaic assistance. A continuous-based model is proposed to optimize critical network design variables, including time-varying headway, stop spacing, and deployment of depot chargers. Introducing rooftop solar photovoltaics can significantly reduce range anxiety for electric buses. Compared with conventional electric bus systems, 4.2%–7.8 % daily in-operation time can be extended, while at most 5.7 % fleet size can also be saved per day. The proposed system demonstrates much more advantages in regions where hourly solar irradiance exceeds 1000 W/m2. Sensitivity tests indicate that (1) with a 10 % improvement in energy conversion efficiency, 1.2 % daily fleet size and 7.5 % depot chargers can be reduced; (2) every 50-kWh increase in bus battery capacity would bring a 1.8 % increment in system cost. Increasing the installation area of solar panels can help reduce battery capacity and lower the system cost. A real-world-based case in Panjin City, China is further designed to validate the application of the proposed system.