2009 State of the Market Report
As described above, intermittent resources cannot currently be dispatched by the real-time market when output reductions are needed to prevent a transmission constraint from being overloaded. Instead, the Midwest ISO operators manual dispatch the wind resources to reduce their output as needed to manage overloaded transmission constraints. Figure 48 shows all of the Midwest ISO’s manual dispatch actions.
Average Amount Curtailed per Interval (MW)
Figure 48: Manual Redispatches 2009
Negative (Non-Wind) Positive (Non-Wind) Negative (Wind)
The vast majority of manual redispatches were of wind units. On average, 25 MW of wind was curtailed per interval in 2009. Wind units were curtailed in 36 percent of intervals, with an average of 70 MW per interval. During certain intervals, as much as 600 MW was manually redispatched. The manual redispatch of non-wind units was exceedingly rare, averaging less than 1 MW per interval.
The manual curtailment of wind units is not generally an efficient means to manage congestion. Additionally, it does not allow congestion to accurately reflect the marginal costs incurred to manage the congestion. The Midwest ISO is currently working on an initiative to allow wind units to be dispatchable through the real-time market and to set LMPs. This initiative will create a new resource category called Dispatchable Intermittent that allows wind resources to respond