2009 State of the Market Report
Load and Resources
This raises a potential concern regarding over-commitment in the peak hours which can suppress peak pricing. We evaluate this topic later in Section IV of the report. Due to the mild conditions during the summer, there were no situations that required the Midwest ISO to call for load interruptions or demand response curtailments during the summer peak periods.
Finally, this figure also shows changes in total generation capacity. The most notable change is the 6 GW increase in September associated with the additions of MidAmerican and Muscatine. Other monthly differences in total capacity are due to the variability of intermittent generation in each peak hour (unavailable intermittent capacity is not shown). To better depict the unavailable capacity in the peak hours, Figure 12 shows only deratings, outages, and other offline capacity.
85,675 80,320 75,702 66,927 70,100 96,497 82,708 90,878 80,103 70,789 76,354 87,108
Figure 12: Capacity Unavailable during Peak Hours 2009
Offline Outage (Planned)
Offline Outage (Forced)
Offline Not Committed
Online Outage Deratings
Online DA Deratings
Deratings in the day-ahead market (shown in bright blue) were higher during summer months, which may be attributable to high ambient temperatures that reduce the capability of some types of generators. The figure shows large quantities of uncommitted generation in every month (exceeding 30 GW on average), due in part to the decline in peak monthly demand in 2009. Also, planned outages are lowest in the summer and, as a result, the larger universe of units in service adds to the total non-outage deratings. In addition, over 7.6 GW of capacity is