**2. Rule-Based Design Process Assumptions**

Here we review rule-based design logic from a prior study [8] for fuel cell-powered trucks. In the U.S. Department of Energy, all vehicles are classified based on the gross vehicle weight rating (GVWR), ranging from class 1 to class 8 [17]. We focus on a class 4 delivery van and a class 8 linehaul truck as shown in Table 1 for conventional vehicle simulations. Control algorithms and component sizes determine whether the vehicles are charge-sustaining or range-extended hybrids. There are two powertrain architectures. One is a battery-powered electric vehicle with a fuel cell range extender, called a FCREx. The other is a fuel cell-dominant system with a battery for peak acceleration events, which is known as a fuel cell hybrid electric vehicle (FCHEV). In FCRExs, the electric machine is sized to match baseline vehicle performance. The fuel cell meets the demands of continuous loads. The battery can assist on a road with a 6% grade for 18 km and is sized to drive 50% of daily driving range in electric vehicle (EV) mode, using only electric power. The hydrogen storage is sized to extend this range. The electric range assumption may not be optimum in this case, but it serves as the FCREx baseline for this analysis.


**Table 1.** Conventional vehicle simulations.

Likewise, FCHEVs are also evaluated for performance. Fuel cells are sized to meet continuous loads for cruise and grade. The electric machine is sized for performance. The battery is sized for both performance and regenerative braking. Hydrogen storage is sized to satisfy daily driving requirements. We see that this sizing approach results in fuel cell-powered trucks that can match or outperform conventional vehicles, with no sacrifices in payload. More information is found in [8]. One limitation of this study was that it did not consider the cost of building or operating the truck. In this paper, we propose an optimum sizing process for fuel cell-powered trucks that will minimize ownership cost while ensuring that performance goals are met.
