2009 State of the Market Report
Load and Resources
Generator Availability and Outages
In this section, we examine the availability of generation capacity, particularly in peak-load hours when resource availability is most important. Figure 11 shows the status of generation capacity during the peak-load hour of each month in 2009.
Figure 11: Availability of Capacity during Peak Hours 2009
150,000 140,000 130,000 120,000 110,000 100,000 90,000 80,000 70,000 60,000 50,000 40,000 30,000
Permanent Deratings Offline Outage (Planned) Offline Outage (Forced) Offline Not Committed Online Outage Deratings Online DA Deratings Online RT Deratings Emergency Range Headroom Generation Plus Reg/Spin Peak Load
Apr 6 May 27 Jun 25 Jul 28 Aug 10 Sep 10 Oct 15 Nov 30 Dec 10
85,675 80,320 75,702 66,927 70,100 96,497 82,708 90,878 80,103 70,789 76,354 87,108 Peak Load
For reference, the peak load in each hour is shown as a red diamond. Most of the load is served by Midwest ISO generation, as indicated by the bottom (blue) segment of each bar. The next two stacked segments in the figure are (1) “headroom”, which is the amount of economic capacity remaining on the committed units above their dispatch point, and (2) the emergency output range. These three segments together represent the total online capacity. The other segments comprise the remaining total capacity that cannot be dispatched for various reasons.
The figure shows that peak load was higher than the total online capacity during most months, which is consistent with the fact that the Midwest ISO relies upon imports to satisfy its demands for energy and operating reserves. The figure also shows that headroom on the highest load days was generally low and near the expected dispatch margins. However, during each of the two highest monthly peaks (June and August), headroom at the peak hour was more than 2,500 MW.