PacifiCorp 2007 Integrated Resource Plan (May 30, 2007)

PacifiCorp – 2007 IRPChapter 4 – Resource Needs AssessmentAs can be seen from the average annual growth rates at the bottom of the Table 4.2, the easternsystem continues to grow faster than the western system, with an average annual growth rate of3.2 percent and 0.8 percent, respectively, over the forecast horizon.System-Wide Coincident Peak Load ForecastThe system peaks are the maximum load required on the system in any hourly period. Forecastsof the system peak for each month are prepared based on the load forecast produced using themethodologies described in Appendix A. From these hourly forecasted values, forecast peaksfor the maximum usage on the entire system during each month (the coincidental system peak)and the maximum usage within each state during each month are extracted.The system peak load is expected to grow from the 2005 peak of 8,937 megawatts at a faster ratethan overall load due to the changing mix of appliances over time. Table 4.3 shows that for thesame time period the total peak is expected to grow by 2.6 percent. The system peak, which previouslyoccurred in the winter, has switched to the summer as a result of these changes in appliancemix. The change in seasonal peak is due to an increasing demand for summer space conditioningin the residential and commercial classes and a decreasing demand for electric relatedspace conditioning in the winter. This trend in space conditioning is expected to continue. Therefore,the disparity in summer and winter load growth will result in system peak demand growingfaster than overall load. However, once the demand in space conditioning equipment stabilizes,the total load and system peak growth rates should equalize.Table 4.3 – Historical and Forecasted Coincidental Peak Load Growth RatesAverage AnnualGrowth Rate Total OR WA WY CA UT ID1995-2005 1.9% (1.1)% (1.0)% (0.9)% 1.9% 7.3% 5.8%2007-2016 2.6% 1.2% 1.2% 5.8% 1.2% 2.9% 1.2%Again, PacifiCorp’s eastern system peak is expected to continue growing faster than its westernsystem peak, with average annual growth rates of 3.2 percent and 1.2 percent, respectively, overthe forecast horizon. This is similar to historical growth patterns as Table 4.3 reflects. East systempeak growth during this time has been faster than west system peak growth. Of course, peakgrowth is somewhat masked in Table 4.3 if you consider that the peak has shifted from wintermonths to summer months.Table 4.4 shows the average annual coincidental peak growth occurring in the summer monthsfor 1995 through 2005. This shows that some of what appears to be a decrease in peak load inmany states is due to the shift from winter to summer, and that growth in peak is truly occurring.It also shows that faster growth is continuing to occur in the eastern portion of the system whereaverage historical growth has been 2.8 percent, while the western portion of the system grew at1.1 percent on average. This pattern is expected to continue as discussed previously.64