Fuel Cell Auxiliary Power Systems

Rogers, W., Shekhawat, D., "Processing of Diesel for Fuel Cell Auxiliary Power Systems",... 

IV.F.2 Assessment of Fuel Cell Auxiliary Power Systems for Onroad Transportation Applications... 

Identified diesel-based 5-kWe fuel cell auxiliary power unit (APU) system with >50% electrical conversion efficiency... 

Sgroi, M., Bollito, G., Saracco, G. and Specchia, S. (2005) BIOFEAT Biodiesel fuel processor for a vehicle fuel cell auxiliary power unit. Study of the feed system. J. Power Sources, 149, 8-14. 

Another important area is the use auxiliary power systems (AFU), which are expected to be one of the first niche applications for fuel cells in the transport area. Auxiliary power today represents a significant portion of the power needs for transportation. Developments of AFUs may also have an impact in the stationary area. 

The system efficiency is lower than the stack efficiency due to power requirements for auxiliary components and due to power conversion. A well-designed system should not use more than 10% of the fuel cell output power for auxiliary components. The efficiency of DC/DC or DC/AC converters is relatively high (typically >90%) but their number and configurations must be optimized for given application. 

With areal power outputs only 20-30% that of a PEFC and an energy-conversion efficiency of 30% near peak power versus 50% in the case of the PEFC, the DMFC remains of great interest because of the attractive properties of methanol fuel, a liquid of high energy density under ambient conditions, and because the DMFC enables direct conversion of this liquid carbonaceous fuel to electric power. Particularly in portable applications, these features help minimize the overall dimensions of the power system (fuel + fuel cell + auxiliaries) and achieve high system energy density. 

For energy security reasons, the presence of an auxiliary power supply unit is necessary. This unit can be preferably either a hydrogen internal combustion engine (H2 ICE) or a fuel cell of corresponding capacity to meet at least the minimum needs of the system. In this case, the system is an autonomous power plant. Figure 5.11 shows a stand-alone wind-hydrogen system that is autonomous. The dashed line in some parts of it implies that these connections may not exist as well. The DC/AC converter/controller should have the capability to operate vice versa and power up the lines through the power controller. 

The modular design of the HyPM fuel cells allows scaling for higher power requirements using a variety of configurations, such as series and parallel systems. Potential applications for the technology include vehicle propulsion, auxiliary power units (APU), stationary applications including backup and standby power units, combined heat and power units and portable power applications for the construction industry and the military. 

Therefore, methanol is the top candidate because of its low price, less toxicity, high energy density and easy handling. Although direct methanol fuel cells may need an auxiliary system to treat unoxidized or partially oxidized fuel in the exhaust gas, direct methanol fuel cells are still a very attractive system as a portable power source. 

In addition to high-profile fuel cell applications such as automotive propulsion and distributed power generation, the use of fuel cells as auxiliary power units (APUs) for vehicles has received considerable attention (see Figure 1-9). APU applications may be an attractive market because it offers a true mass-market opportunity that does not require the challenging performance and low cost required for propulsion systems for vehicles. In this section, a discussion of the technical performance requirements for such fuel cell APUs, as well as the current status of the technology and the implications for fuel cell system configuration and cost is given. 

Electric Power System Design For specific applications, fuel cells can be used to supply DC power distribution systems designed to feed DC drives such as motors or solenoids, controls, and other auxiliary system equipment. The goal of the commercial fuel cell power plant is to deliver usable AC power to an electrical distribution system. This goal is accomplished through a subsystem that has the capability to deliver the real power (watts) and reactive power (VARS) to a facility s internal power distribution system or to a utility s grid. The power conditioning... 

Develop a fuel cell system for auxiliary power units (3-30 kW) with a specific power of 150 W/kg and a power density of 170 W/L by 2010. 

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