Integrating transmission into IRP part II: case study results

This is Part II of a two paper set dealing with transmission and integrated resource planning. Part I described an analytical approach to integrating transmission into the IRP framework and set forth the Comprehensive Electrical Systems planning Model (CESPLAN). The model, a mixed integer, nonlinear, stochastic programming formulation of the planning problem is solved using the generalized Benders decomposition algorithm with importance sampling to couple the contingency state space. The primary objective of this paper is to report a series of case studies performed with the model. Three sets of case study results are reported. The first set illustrates that optimal resource plans created from the commonly used utility approach of two-step planning, i.e., first planning generation and demand-side resources and then determining the set of transmission resources that “best matches” the generation and demand-side plan, can lead to higher costs than when a more comprehensive, integrated planning approach is adopted. A second set of case studies illustrates the use of “importance sampling”, a procedure for reducing the number of sample configuration states of the system that must be simulated when estimating the effects of equipment outages on future system operating costs. The third set of studies illustrate not only the optimal generation plan but also the optimal transmission plan is sensitive to planning uncertainties such as emissions allowance costs, customer outage costs, and future natural gas prices