Model study of a fuel cell range extender for a neighborhood electric vehicle (NEV)

Abstract

Abstract Fuel cell systems have the potential to provide high-efficiency, low-cost power for Neighborhood Electric Vehicles (NEVs). Model results are presented examining the utility of placing a hydrogen PEM fuel cell on-board a Miles Electric ZX40ST work truck NEV as an “after-market add-on” range extender to the existing battery electric drive train, thereby creating a NEVx. Through the development and use of the Sandia-Miles-Altergy Range Test (SMART) model, we have examined the potential for a number of PEM fuel cell stack systems (with varying output power), combined with various hydrogen storage and electrical storage system configurations to achieve the desired range extension for a single 8-h work shift. Furthermore, we have evaluated the “well-to-wheels” (WTW) and greenhouse gas (GHG) reductions, and assessed the costs (both capital and O&M) for the different NEVx configurations and operating profiles. This analysis demonstrates that a NEVx incorporating a PEM fuel cell range extender provides a viable means of providing the desired range (or equivalently the runtime) while increasing the vehicle's versatility and maintaining its zero-emissions rating. A 5 kW fuel cell system with 2.6 kg of hydrogen stored at 2265 psi in conventional steel cylinders can meet the demands of the low-power duty cycles envisioned for the NEVx. A slightly higher powered NEVx with a 7.5 kW fuel cell offers the same advantages in operating profiles that require more power, for example with frequent starts, sustained higher speeds, or hilly routes. While currently expensive, the total cost per mile of the fuel cell range extender is comparable to conventional gasoline vehicles. The WTW GHG emissions of the NEVx are 40%–85% lower than those for a comparable gasoline powered vehicle, depending on the particular drive profile and sources of both hydrogen and electricity. The analysis shows that a fuel cell range extender can maintain the vehicle battery pack at a high state of charge (SOC) throughout the operating profile, thereby extending overall battery life and reducing charging time. The fuel cell range extender is currently envisioned as a drop-in retrofit for the existing Miles Electric ZX40ST work truck. However, with sufficient demand, a fully integrated new vehicle system could be both more efficient and less expensive. If designed into the NEVx from the start, the cost, weight, and emissions could all be reduced while increasing the payload space and versatility.