Evaluation of individual cell voltages in stack Sample Clauses

Evaluation of individual cell voltages in stack. In order to assess the precision in data used for calculation of degradation rates and lifetime prediction, more than one measurement is required. Optimally, a population of identical stacks running under identical ambient and operational conditions should be available for statistical evaluation. This is rarely the case. For a single stack, the individual cell voltages can be utilized in order to evaluate the variance. More interesting than the average cell voltage and its corresponding standard deviation is the distribution of the population. Stack geometry will affect the distribution of individual cell voltages. From a design point-of-view, it is of interest to evaluate individual cell degradation rates in order to verify stack design. From evaluation of individual cell voltages in the stack, deviation in the end cells were observed. Therefore, the two outermost cells at each end of the stack were excluded from further cell voltage evaluation. So, in this particular exercise, 43 cells were used to evaluate the population distribution. In order to improve distribution assessment, 1 Hz data was used where 200 seconds of individual cell voltages were used to create voltage populations. At Beginning of Test (BoT), the distribution is best described normally, as shown in Figure 5. Figure 5. Probability density (left) and probability (right) plots for BoT data (November 2011). Figure 6. Probability density (left) and probability (right) plots in June 2012.