2009 Scenario Reliability Assessment - NERC

Scenario Reliability Self-Assessmentsa study of the Renewable Portfolio Standard (RPS) required by the various Western states, andproduced a weighted average renewable energy use of 8.8 percent. The Scenario Case was anextension of the base case and increased the renewable energy requirement to 15 percent. Theexisting resources, both conventional and renewable, were the same in both cases, but renewableresources were added to the different cases to satisfy the RPS requirements. These cases will bereferenced in this report as the base case for the 8.8 percent RPS case, and Scenario Case for the15 percent case.WECC studied the 2009 Scenario Case with an hourly simulation of the year 2017 as part of theTEPPC 2008 study program. 104 This study used loads from the 2007 forecasts, since the 2008forecasts were not available, though there were some updates from 2008 forecasts; one of themdriven by the requirements of the hourly simulation. The load adjustments, described on thesecond page of “Attachment - WECC Study Results” (the Attachment), did not significantlyaffect the outcome of the study or the conclusions to be drawn from it. Generation was drawnfrom the data submitted for the 2008 Long Term Reliability Assessment (LTRA) data request,modified to develop a study case with 15 percent renewables penetration.It is important to note that the Scenario Case was a constructed example of one geographic andrenewables mix among a number of possible ways to meet one forecast of 2017 load levels. Justas the absolute levels of the load are not crucial to the conclusions that can be drawn from thestudy, neither are the exact specifications of the resource build out. The scenario was constructedby TEPPC to be a reasonable build out given the types of renewable generation currently beingconsidered by Western entities, taking account of likely geographic diversity and resourcequality available at different locations in the Western Interconnection.The scenario was designed to be adequate, so it is not a test of the adequacy of a high renewablespenetration scenario. Nonetheless, it was clear in the course of developing the scenario thatadequacy issues were raised that need to be addressed, and WECC has developed a process foraddressing them.Moreover, since the modeling was in hourly time steps, the operating issues raised by variablegeneration, in particular wind since it is expected to make up a large percentage of therenewables that are developed in the Western Interconnection, were not apparent from themodeling. These issues are, however, known from other studies and from the ongoing operatingexperience of Western BAs that are already experiencing high renewables penetrations.DiscussionThe renewable generation making up the 15 percent case was approximately 44 percent wind, 15percent solar, 32 percent geothermal, and nine percent biomass. Much of this generation wassited relatively near major load centers, so that the transmission requirements though significant,were not entirely large, long-distance lines. For instance, much of the solar generation waslocated relatively near the major load centers of Phoenix and Southern California. The104 A security-constrained economic dispatch model using a DC load flow, PROMOD, was used for this study. Thehourly simulation study done by TEPPC, which developed the transmission implications of the scenario, wassupplemented by an analysis of the same data with a simplified version of PROMOD to develop other aspects ofthe study.2009 Scenario Reliability Assessment Page 151