Practical experience in evaluating adequacy of generating capacity in the Western interconnection

Paper presents practical experience in evaluating adequacy of generating capacity by different regions in the Western interconnection. This includes analysis of uncertainties associated with load, intermittent energy sources and forced and maintenance outages on generating units and transmission facilities. The paper is a joint effort by the utility industry and Western Electricity Coordinating Council (WECC). Adequacy assessment of systems with ongoing integration of variable resources such as wind and solar has added new requirements to enhance the present methodologies and tools for computing the known Loss-of-Load-Expectation (LOLE) index. The LOLE index is influenced by load, generation, export/import, generation and transmission forced and maintenance outages, transmission operating constraints and various uncertainties related to load, generation and system operating conditions. Application of probabilistic approaches has already been used by industry and is accepted by a number of WECC member utilities. Adequacy indexes such as LOLE and Expected Unserved Energy (EUE) allow the meaningful assessment of the effective generating capacity margin and help utilities to determine if new resources are needed to meet reliability standard. This paper reviews the probabilistic approaches presently used by utilities in Western Interconnection in regard to planning and operating generating resources.