Plug-in vs. Wireless Charging: Enhancing Sustainability of Urban Electric Bus Systems
Wireless charging is an alternative method for charging battery electric vehicles (BEVs) in contrast to the conventional method of plug-in charging. Wireless charging allows BEVs to charge either in motion or in stationary status through electromagnetic resonance, and can be especially advantageous for BEVs with fixed routes. This study utilizes an integrated life cycle assessment and life cycle cost (LCA-LCC) model to provide a comprehensive framework evaluating charging options for enhancing urban bus transit sustainability. The life cycle energy, greenhouse gas (GHG) emissions and costs associated with a stationary wireless charging all-electric bus system are compared to a plug-in charging all-electric bus system.
The transit bus system operating in Ann Arbor, Michigan is used as the basis for a case study. The bus fleet is assumed to be all-electric and two charging scenarios are compared: (1) the plug-in charging scenario and (2) the wireless charging scenario. Detailed inventory analysis of wireless and plug-in chargers is conducted. Results show that the wireless charged battery can be downsized to 27-44% of a plug-in charged battery. The associated reduction of 12-16% in bus weight for the wireless buses can induce a reduction of 5. 4-7. 0% in battery-to-wheel energy consumption. The integrated LCA-LCC model highlights the tradeoffs of BEV wireless charging. Although there are higher initial infrastructure burdens from off-board wireless chargers deployed across the service region, the wireless charging bus system results in lower use-phase energy consumption, GHG emissions and costs due to the lightweighting benefits of onboard battery downsizing. Overall, wireless charging system is comparable with plug-in charging system in terms of life cycle energy, GHG emissions and costs. Further sensitivity and uncertainty analyses are conducted. To further improve the life cycle performance of the wireless charging bus system, it is important to consider the key parameters identified by further sensitivity analysis, such as carbon intensity of the electric grid, wireless charging efficiency, unit price of lithium-ion battery pack, cost of off-board wireless charging infrastructure and day or night electricity price.