2009 State of the Market Report
of active constraints had a pivotal supplier, up from 59 percent in 2008. In all, these results indicate that while local market power is most commonly associated with the NCA constraints, a large share of BCA constraints in 2009 raised potential local market power concerns as well.
The prior analysis showed that a supplier was frequently pivotal when a BCA constraint or NCA constraint was active. Figure 75 shows the percentage of all market intervals when at least one supplier was pivotal for such a constraint. This analysis varies from the prior analysis because it incorporates how frequently BCA and NCA constraints are active. Therefore, it measures how frequently local market power may be a problem within the Midwest ISO.
Figure 75: Percent of Intervals with at Least One Pivotal Supplier 2009
Share of Intervals
BCA Constraints WUMS NCA Constraints Minnesota NCA Constraints
There was an active BCA constraint with at least one pivotal supplier in 79 percent of the hours during 2009, up 13 percentage points from 2008. As in prior years, the regional distribution of BCA constraints varied by month, with the Central region experiencing more constraints than the other three regions. The monthly frequency ranged from 62 percent to more than 90 percent. NCA constraints had a pivotal supplier in substantially fewer hours than BCA constraints did because there were fewer NCA constraints. There was an active NCA constraint with a pivotal supplier in only 17 and 21 percent of hours in WUMS and Minnesota, respectively. These