Three probabilistic metrics for adequacy assessment of the Pacific Northwest power system

All regional power system entities within the bulk assessment areas in North America calculate and report probabilistic adequacy metrics that measure projected shortfall duration and magnitude to the North American Electric Reliability Corporation (NERC). While no maximum thresholds have been defined for either metric to be used as an adequacy standard, it is possible that such thresholds could be defined sometime in the future as planners gain a better understanding of the risks associated with each metric and how they interact. Therefore, it is prudent to know whether setting a threshold for one metric automatically leads to an equivalent and predictable threshold for the other. To answer this question, this paper examines mathematical relationships among these two metrics and a third metric (that measures the projected shortfall frequency) for the Pacific Northwest power supply. Results from a Monte Carlo simulation model show that although in special cases the threshold for one metric can be used to calculate unique thresholds for the other two, in general this is not the case. Hence, if these metrics are to be used to define an adequacy standard for the Northwest, threshold values for all three metrics should be defined independently.