Cell design capital costs

Capital costs for fuel cell power systems vary with production rates, peak power voltage conditions, and hydrogen source (reformate vs. direct). As with most manufactured products, the cost of materials, manufacturing, and assembly decrease with increasing annual production volumes. Designing the fuel cell stack to operate at lower voltages at peak power (0.6 V/cell vs. 0.7 V/cell) offers capital cost savings at the expense of system efficiency. 

Producers have developed specific cell configurations to optimise electricity consumption, cell capital, and operating costs. Pacific Engineering Corp., Kerr-McGee Chemical Corp., Chedde Pechiney, Cardox Corp., Electrochemie Turgi, American Potash and Chemical, and I. G. Earbenindustrie each has a unique cell design. 

A simple cell design is required to reduce capital costs. The cost of the raw materials, HF and electricity, are not negligible, but they are minor. The pilot plant cell design shown in Fig. 16 is derived from the callandria cell developed for the Phillips ECF process.14 The cell body and internals are of mild steel pipe selected to be resistant to hydrogen embrittlement. Figure 17 is a horizontal section through the working part of the cell. 

The design and optimization of a fuel cell power system is very complex because of the number of required systems, components, and functions. Many possible design options and trade-offs affect unit capital cost, operating cost, efficiency, parasitic power consumption, complexity, reliability, availability, fuel cell life, and operational flexibility. Although a detailed discussion of fuel cell optimization and integration is not within the scope of this section, a few of the most common system optimization areas are examined. 

The designer has the ability to increase the overall utilization of fuel (or the oxidant) by recycling a portion of the spent stream back to the inlet. This increases the overall utilization while maintaining a lower per pass utilization of reactants within the fuel cell to ensure good cell performance. The disadvantage of recycling is the increased auxiliary power and capital cost of the high temperature recycle fan or blower. 

Oxidant Utilization In addition to the obvious trade-ofFbetween cell performance and compressor or blower auxiliary power, oxidant flow and utilization in the cell often are determined by other design objectives. For example, in the MCFC and SOFC cells, the oxidant flow is determined by the required cooling. This tends to yield oxidant utilizations that are fairly low (-25%). In a water-cooled PAFC, the oxidant utilization based on cell performance and a minimized auxiliary load and capital cost is in the range of 50 to 70%. 

The Rolls-Royce plan was mapped out at the Seventh Grove Symposium (Agnew 2001), and is based on optimisation of the current, all-ceramic design as part of a gas turbine hybrid. The Rolls-Royce gas turbine will be optimised for hybrid service. The potential of its fuel cell, for cheapness via mass production, is stressed in its patents. Capital costs could come down to 300/kWe. There are no signs up to 2005 of a Rolls-Royce ITSOFC waiting in the wings. 

Accurate cost figures for processes early in development are impossible to project. However, it is possible to roughly estimate the power and capital requirements to assess viability. The power consumption is overwhelmingly due to tile cell current, which is near stoidtiometric. Cell voltage, as shown earlier, can be estimated with reasonable accuracy. Capital costs can be estimated by analogy with MCFC stacks, whose design these membrane cells will mimic. 

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