65 Operating Parameters

Fuel cell performance is affected by operating parameters such as temperature, pressure, reactant gas concentrations, reactant utilizations, and current density. These parameters determine the ideal cell potential as well as the magnitude of the losses described above. There is a wide variety of operating points that can be selected for a specific design, and the modification of oper ating parameters can have beneficial effects on system performance in one case and detrimental effects in the other.

To illustrate just one of the design considerations, Figure 6.7 presents the typical relationship between voltage and power levels for a fuel cell. One would typically desire to operate a fuel cell at its maximum current density to reduce the required size and potentially reduce the cost of the fuel cell. However, as Figure 6.5 indicates, this leads to operation at lower voltage levels which lowers the available voltages and cell efficiency as indicated above. Typically, fuel cells are designed to operate at a point that yields a good compromise of low operating cost (higher cell efficiency at higher voltages and lower power densities) and low capital cost (less cell area due to higher power densities and lower voltages). This is further complicated by the fuel cell system requirements, which may dictate overall volume limitations or require certain levels of heat generation within the stack to provide the fuel reformer with sufficient heat to overcome the endothermic reforming reactions.

In the following paragraphs, further considerations are made for the effects of operating conditions such as temperature and pressure on fuel cell performance.

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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