The Council released its last assessment of Northwest power supply adequacy for the winter of 2001-2002 in early June of this year. That assessment relied on data, assumptions and analysis largely developed over the previous month. It found that given the then-current assessments of the demands for electricity across summer and subsequent fall and winter, new generation, and hydro conditions, the probability of winter season power supply inadequacy was approximately 17 percent.1 The analysis went on to assess the efficacy of storing additional energy in Arrow reservoir in Canada in reducing winter power supply problems. It was found that storing an additional 1,500 megawatt-months of energy (in addition to 1,200 megawatt-months already planned to be stored) reduced the probability of inadequacy to about 12 percent. Additional amounts of storage did not significantly reduce the probability, largely because of restrictions on the rate at which water could be withdrawn from the reservoir. On the basis of this and other similar analyses, decisions were made to dramatically reduce spill at federal hydroelectric projects and seek additional opportunities for reducing electricity demands.
The Council recently completed a reassessment of the winter power supply situation based on updated data and analyses. This analysis found the probability of winter season power supply inadequacy to be well under the target level of 5 percent. This is attributed primarily to two factors. First, expected demands for electricity are significantly lower than estimated in the May analysis. This is attributable to several factors: efforts on the part of utilities to buy out industrial loads, particularly the aluminum industry; conservation efforts, the expected effects of retail rate increases and the general slowdown of the economy. The other major factor is improved hydro storage conditions. Instead of 1,500 megawatt-months of energy stored in Canada, 3,700 megawatt-months were stored.2 This additional storage was made possible by the drastically reduced spill this summer and by the fact that loads were lower than expected throughout the West. In addition, the constraints on the rate at which this energy could be withdrawn were relaxed, making the stored energy more effective in addressing periods of high demand.
The analysis and the results are described in more detail in the following sections.
[1] The winter season is defined as the months of December, January, February and March. A winter season was judged to have an inadequate power supply if loads exceeded available energy by a seasonal average of 10 average megawatts or more.
[2] This is in addition to the storage of 1,200 megawatt-months of energy that was already planned and was included in both the May and October studies.
