Adequacy Assessment of the Idaho Power Generation System with Integrated Variable Energy Sources

As we move into the future, variable energy resources (VERs), such as wind and solar, will begin to dominate utilities resource portfolios. We see indicative signs of this in the western interconnection with utility Integrated Resource Plans (IRPs) bypassing the natural gas "bridge resource" and identifying copious quantities of wind and solar in their 20-year plans as they work to retire increasing amounts of higher energy-cost fossil-based resources – especially coal. Adequacy assessment of systems with ongoing integration of VER, has added new requirements to enhance the current methodologies and tools for computing the widely-used Loss-of-Load-Expectation (LOLE) index. This paper presents the practical experience in evaluating the adequacy of the Idaho Power Company (IPC) generation system with integrated VER such as wind and solar. In this paper the adequacy assessment includes an analysis of uncertainties associated with load, limited energy sources (hydro), variable wind and solar energy sources, and forced and maintenance outages of generating units. The transmission contingency driven constraints have not been considered. The adequacy indexes, such as LOLE and Expected Unserved Energy (EUE), are calculated by using an analytical convolution approach that considers the realistic time series of available generation produced by VER, such as hydro, wind and solar. This paper explores, compares and presents the reliability results of four top Idaho IRPs portfolios that are selected among the 24 studied portfolios based on the cost and risk. The results suggest that the portfolio that includes a new transmission line, wind, and solar resources has the highest reliability and was one selected by IPC. In addition, the case study results indicate which wind and solar resources by location will provide more value in reducing LOLE index and show the impact of Load Forecast Uncertainty (LFU) on the LOLE and EUE indexes. The capacity contributions of future VER are also evaluated by using the Effective Load Carrying Capability (ELCC) approach across five different meteorological profile years (2015-2019).