Studies of Energy Consumption by a City Bus Powered by a Hybrid Energy Storage System in Variable Road Conditions

This article analyzes various configurations of Hybrid Energy Storage Systems consisting of batteries only, combinations of batteries and supercapacitors, and supercapacitors only. For the presented configurations, mathematical models that were used in research in terms of energy consumption and carbon dioxide emissions were developed, employing a 12-m city bus as a test bed. The tests were carried out using standard test cycles for heavy vehicles as well as routes developed on the basis of actual road conditions. The obtained test results confirmed that the lowest energy consumption is characterized by the system supplied exclusively by batteries (855 Wh/km), followed by a hybrid system of a large battery with a small supercapacitor (941 Wh/km), a hybrid system with a large supercapacitor and a small battery pack (1087 Wh/km), and finally a system with a supercapacitor only (1091 Wh/km). In comparison with the conventional diesel power system (3967 Wh/km), the CO2 emission reductions ranged from 27% to 43%, depending on the source of electrical energy.