PhD Thesis - Energy Systems Research Unit - University of Strathclyde

varies with the type of electrolyte being used, and its required working
temperature, although scaling the same fuel cell design up or down has little
effect on the efficiency.
Interestingly, the efficiency of a fuel cell stack alone increases at lower loads, as
shown in Figure 5.18 [23]. This increase in efficiency, however, varies
substantially with the overall plant design, and some fuel cell generating sets can
show efficiency values that increase, decrease or stay reasonably constant at
lower loadings [24]. This can be seen in the overall curve in Figure 5.18, which
shows the fuel in to electricity out efficiency of an overall fuel cell
configuration.
Figure 5.18 Typical Efficiency of a Fuel Cell Under Partial Loading [23]
5.6.3 Multiple Fuel Cell Generation Sets
As the efficiency of a fuel cell may increase under partial load, this must be
taken into consideration when deciding the optimum share of load between
multiple fuel cells when more than one is specified in a generating set. If
efficiency decreases with partial load, the load share is determined as described
for multiple engine sets in Section 5.2.5. If efficiency increases with decreasing
load, as shown in Figure 5.18, a different approach must be taken. This is
outlined below, and shown graphically in Figure 5.19. Again, it has been
assumed that it is more efficient to run a number of fuel cells at the same
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