The Phase 1 fuel cell bus has been operated on UD's campus shuttle bus routes since May 2007, as a technology demonstration and to evaluate its performance and reliability. The bus is normally driven each day for about 2.5 hours, carrying about 100 passengers, and the data acquisition system collects a comprehensive set of data on the vehicle's operation, which is automatically stored on a server at the FCRL.
After about two years of operation, the data was analyzed, with a particular focus on fuel cell system efficiency and availability. Although the fuel cell system was not very reliable when the bus started operation, matters improved considerably over time as design problems were addressed:
Power flow in the bus was also examined to identify possible areas for improvement in efficiency. A tool called a Sankey diagram, which shows power flows as "streams" with width proportional to their magnitude, was used. It shows the large amounts of energy recovered by regenerative braking with a large battery bank to absorb the power coming from the traction motor:
The fuel cell system balance of plant consumes a significant fraction of the energy of the hydrogen supplying the stack, so efficiency gains there are potentially quite useful. Most of the balance of plant energy feeds the air compressor, so efficiency could be increased by improving air humidification to allow lower air system backpressure; additional improvements can be realized by replacing the hydrogen recirculation pump with a variable flow ejector.