2010 Report - Pennsylvania Public Utility Commission

Figure 16 Pennsylvania non-coincident peak load and annual growth10Annual Growth86Forecast33,00031,00029,000Percent Change420-2-4-6-8-10Peak Load27,00025,00023,00021,00019,00017,00015,000Megawatts-1213,000Trends in Forecast AccuracySince electricity use is a function of several forces outside the control of the utilities, forecasts offuture electricity requirements cannot be any more certain than the forecasts of those externalforces. Although all utilities have had some degree of difficulty in adjusting to the dramaticchanges in electricity use, some utilities have fared better than others. This may, in part, beattributable to the stability (or volatility) of each utility’s service territory.During the 1970s and early 1980s, forecast deviations from actual figures quickly becameexcessive. Forecasts of peak load made three years in advance were, on average, 10 percent higherthan actual demand. Forecasts made five years in advance were 20 percent higher. Over the lastfew years, however, forecast deviations have shown no appreciable difference as to whetherforecasts are made one, two or even five years in advance. Peak load forecast deviations havevaried only slightly, from 4.7 percent to 5.7 percent, based on the average of forecast deviations foreach company. Deviation magnitudes have diminished over time. See Figure 17. (Available datapoints decrease from 10 for forecasts made one year in advance to six for forecasts made five yearsin advance.)Energy demand forecast deviations have also diminished over time. Unlike the peak loadforecasts, however, there is a definite pattern of increasing forecast deviation magnitudes as theforecasts advance into the future. Figures 18-20 show the absolute deviations from actual for theresidential, commercial and industrial sectors, for forecasts made one to five years in advance.Electric Power Outlook for Pennsylvania 2009-2014 29