2009 State of the Market Report
levels by mid-year, although volumes in ISO-NE declined once more in the second half of 2009 due to a general reduction in congestion and arbitrage opportunities. Virtual load as a percentage of actual load in the Midwest ISO declined by more than one-third from the 2007-2008 levels and remained near 5 to 6 percent of actual load throughout 2009. Virtual supply volumes declined by almost half from previous years, averaging only 3.8 percent of actual load. This is substantially less than in the other markets. As noted above, the high RSG cost allocation rate applied to virtual supply beginning in November 2008 contributed to the decline in virtual supply quantities.
Our next analysis examines the Midwest ISO’s day-ahead forecasted load. Figure 24 shows the percentage difference between the day-ahead forecasted load and real-time actual load for the peak hour of each day in 2009.
Figure 24: Daily Day-Ahead Forecast Error in Peak Hour 2009
Average Peak Load Forecast Error Avg DA Forecast Minus Avg RT Load
DA Forecast Minus RT Load (% of RT Load)
Apr-09 May-09 Jun-09 Jul-09 Aug-09 Sep-09 Oct-09 Nov-09 Dec-09
Day-ahead load forecasting is a key element of an efficient day-ahead commitment process. The accuracy of the day-ahead load forecast is particularly important for the Reliability Assessment