Optimization of Hybrid Energy Storage Systems for Electrified Istanbul-Bus Rapid Transit System

Fossil fuel–driven climate change in the transportation sector has contributed to natural disasters worldwide, prompting a shift toward electric buses (e-buses). While batteries are the primary energy storage systems (ESS) in electric vehicles, their high cost and limited lifespan hinder widespread adoption. This study investigates hybrid energy storage systems (HESSs), which combine batteries with alternative ESS components such as ultracapacitors (UCs), flywheels, or fuel cells (FCs), to improve performance and reduce costs. The study optimizes both the dimensional design and energy management of battery-only, passive, semi-active, and fully active HESS configurations. Optimization criteria include cost reduction, extended battery life-cycle, and minimized overall weight. The results show that, compared to a battery-only system, the optimized HESS configuration increases battery life by 2.55 years at an additional cost of $39,626. In the long term, the optimized HESS system costs $106,694, representing a 44% higher expense than the battery-only configuration. However, when applied to the entire fleet of buses on Istanbul’s Metrobus line, the total cost of the ESS system could be reduced by $1,600,410. This research highlights the potential of HESSs to improve the sustainability, energy efficiency, and cost-effectiveness of electric public transportation networks.