Fleet and Fueling Systems Engineering Analysis
Hydrogen energy systems for transportation applications are at an early stage of development. The configuration and requirements for these systems are only now being defined. The INL recently performed a systems engineering analysis of hydrogen-powered transportation system defined by a fueling station and a fleet of transit buses. The analysis used a structured approach to: (a) identify the most likely system configuration, (b) provide integrated design requirements for the various component technologies, and (c) identify technology gaps and "show stoppers" that must be addressed to implement a hydrogen economy for transport buses.
The proton exchange membrane (PEM) fuel cell technology offers the best prospects for meeting bus engine performance, durability, and cost criteria. However, there are several critical issues that need to be addressed in order for the PEM fuel cell to be a viable alternative for the hydrogen fuel cell bus. Despite recent advances, several technological gaps hinder implementation of current technologies. Further, aggressive pursuit of cost goals, combined with the benefits of mass-production, will be needed to achieve a manufactured costs comparable to the low cost of internal combustion engines.
For near-term applications, on-board storage of compressed hydrogen gas is the preferred method for supplying hydrogen to the PEM fuel cell. Of the four methods considered for hydrogen storage in commercial applications, compressed gas offered advantages in its simplicity, maturity, rapid refueling capability, excellent dormancy characteristics, low infrastructure impact, and low development risk. On-site hydrogen production is preferred over onboard production; the latter option is hindered by complexity, weight, costs, and delay in start-up performance.
The engineering analysis focused on the integration of the fuel supply, vehicle, fuel storage, safety devices, economics, performance, weight, motor, maintenance, reliability, longevity, and over-the-road safety. The initial focus of the study was to identify the cross-cutting and critical-path technologies. Identification of requirements for each of the components in the system provides working parameters for subsequent research and development. Thus, the results form the basis for defining future research and development.