Plug-in vs. Wireless Charging: Life Cycle Energy and Greenhouse Gas Emissions for an Electric Bus System
Wireless charging, as opposed to plug-in charging, is an alternative charging method for electric vehicles (EVs) with rechargeable batteries and can be applicable to EVs with fixed routes, such as transit buses. This study adds to the current research of EV wireless charging by utilizing the Life Cycle Assessment (LCA) to provide a comprehensive framework for comparing the life cycle energy demand and greenhouse gas emissions associated with a stationary wireless charging all-electric bus system to a plug-in charging all-electric bus system. Life cycle inventory analysis of both plug-in and wireless charging hardware was conducted, and battery downsizing, vehicle lightweighting and use-phase energy consumption were modeled. A bus system in Ann Arbor and Ypsilanti area in Michigan is used as the basis for bus system modeling. Results show that the wirelessly 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. In the base case, the wireless charging system consumes 0.3% less energy and emits 0.5% less greenhouse gases than the plug-in charging system in the total life cycle. To further improve the energy and environmental performance of a wireless charging electric bus system, it is important to focus on key parameters including carbon intensity of the electric grid and wireless charging efficiency. If the wireless charging efficiency is improved to the same level as the assumed plug-in charging efficiency (90%), the difference of life cycle greenhouse gas emissions between the two systems can increase to 6.3%.