PacifiCorp 2007 Integrated Resource Plan (May 30, 2007)

PacifiCorp – 2007 IRPChapter 4 – Resource Needs AssessmentLOAD AND RESOURCE BALANCECapacity and Energy Balance OverviewThe purpose of the load and resource balance is to compare the annual obligations for the firstten years of the study period with the annual capability of PacifiCorp’s existing resources, absentnew resource additions. This is done with respect to two views of the system, the capacity balanceand energy balance.The capacity balance compares generating capability to expected peak load at time of systempeak load hours. It is a key part of the load and resource balance because it provides guidance asto the timing and severity of future resource deficits. It was developed by first determining thesystem coincident peak load hour for each of the first ten years (2007-2016) of the planning horizon.The peak load and the firm sales were added together for each of the annual system peakhours to compute the annual peak-hour obligation. Then the annual firm-capacity availability ofthe existing resources was determined for each of these annual system peak hours. The annualresource deficit (surplus) was then computed by multiplying the obligation by the planning reservemargin, and then subtracting the result from the existing resources.The energy balance shows the average monthly on-peak and off-peak surplus (deficit) of energyover the first ten years of the planning horizon (2007-2016). The average obligation (load plussales) was computed and subtracted from the average existing resource availability for eachmonth and time-of-day period. This was done for each side of the PacifiCorp system as well as atthe system level. The energy balance complements the capacity balance in that it also indicateswhen resource deficits occur, but it also provides insight into what type of resource will best fillthe need. The usefulness of the energy balance is limited as it does not address the cost of theavailable energy. The economics of adding resources to the system are addressed with the studiesand results of those studies described in Chapters 6 and 7 respectively.Load and Resource Balance ComponentsThe capacity and energy balances make use of the same load and resource components in theircalculation. The main component categories consist of the following: existing resources, obligation,reserves, position, and reserve margin. This section provides a description of these variouscomponents.Existing ResourcesThe firm capacities of the existing resources by resource category are summed to show the totalavailable existing resource capacity for the east, west and for the PacifiCorp system. A descriptionof each of the resource categories follows:● Thermal – This includes all thermal plants that are wholly-owned or partially-owned byPacifiCorp. The capacity balance counts them at maximum dependable capability at time ofsystem peak. The energy balance also counts them at maximum dependable capability, butderates them for forced outages and maintenance. This includes the existing fleet of 11 coalfiredplants, four natural gas-fired plants, and two co-generation units. These thermal re-76