TABLE OF CONTENTS As seen in Chapter 3, the fuel cell electrochemical reactions result in theoretical cell potential of 1.23V, and the actual potential in operation is lower than 1V. If a single cell were required to generate 1kW of power, it would need to generate electrical current higher than 1000 Amperes. Such a current could be generated only with a large active area (>1000cm 2), and it would require very thick cables between the fuel cell and the load in order to minimize the resistive losses. A more practical solution would be to have multiple cells electrically connected in series. The cell active area and the cross-sectional area of the connecting cables would decrease with a number of cells connected in series. For example, 1kW power output may be accomplished with as many as 40 cells connected in series, each cell operating at 0.6V and 1A/cm 2. Total current would be about 42 Amperes at 24 Volts.
The first step in designing a fuel cell stack is to determine its active area and number of cells in the stack. When a stack is designed for an application, the design inputs come from the application requirements, such as desired power output, desired or preferred stack voltage or voltage range, desired efficiency, and volume and weight limitations. Some of these requirements may conflict each other, and the stack sizing and design process often results in a compromise solution that meets the key requirements (such as...
