The PCC Reliability Subcommittee is initiating a process to revise the methodology of its power supply assessments to better ensure data consistency and to develop a metric appropriate for assessing resource adequacy in the Northwest, an energy-constrained, hydro-dominated system. The development of a new metric is scheduled for implementation in 2004. Currently, WECC is undertaking efforts to ensure that the data reported for the ?2003 Loads and Resources (L&R) Report? is consistent.
The purpose of the following questions and answers is to provide specific descriptions of the hydro data requested for the L&R Report to allow for consistent collection of information in 2003.
QUESTION #1: WECC defines ?adverse hydro? as ?Runoff and storage regulation which reflect operation under the most critical stream flow conditions that have occurred during a specified period, usually the period of historical record,? which historical year is reflective of the most critical stream flows in the Northwest?
ANSWER #1: It should be noted that the Northwest is currently discussing the appropriate definition of adverse hydro for this region. For the purposes of the 2003 report, however, the runoff and/or hydroelectric capability associated with the year 1937 meets the WECC definition for?adverse hydro?. Canada has a different ?adverse hydro? year (1940) because the data in Canada for that year is deemed more reliable. Rather than strictly using historical flows, the stream flow for 1937 is modified to reflect the current level of development, i.e. stream flow accretions and depletions are adjusted for agricultural, urban and environmental water usage associated with a recent historical year such as the year 2000.
QUESTION #2: What is the appropriate capability to report for hydroelectric power plants under adverse hydro conditions?
ANSWER #2: In order to achieve consistency for the 2003 report, the appropriate capability to report is sustained weekly peaking capacity for the month of August in the summer assessment and for the month of February in the winter assessment associated with 1937 modified water conditions and forecasted reservoir storage releases. Sustained peaking capacity is defined as that amount of capacity that can be supported by 50 hours of energy per week (10 hours per day for 5 consecutive days) during the most critical month of the season. It is assumed that energy is returned in light load hours. Capacity is reduced from installed capacity to reflect the weighted average head in the reservoir during the appropriate time period. The month of August is the peak load summer month and therefore the most critical month for the Western Interconnection's summer assessment. Although February is not the peak load month in the Northwest, i.e. the Western Interconnection's winter peaking sub-region, the combination of load, low hydroelectric stream flows and the potential for cold snaps make February the most critical month for the Northwest in the winter season.