2009 Scenario Reliability Assessment - NERC

Regional Reliability Scenario Self-AssessmentsWECC conclusions are based primarily on the 15 percent Scenario Case and corresponding basecase, rather than a comparison to the 2008 Long-Term Reliability Assessment case. Because thesecases are constructed to meet study goals, they are not directly comparable to Long-TermReliability Assessment cases since they consist, on the resource side, of a recounting of utilityplans and expectations for independent generation development with varying levels ofconfidence.For the study cases, WECC constructed a resource build-out based on RPS and 15 percentrenewables penetrations, with additional resources submitted by utilities for the 2008 Long-TermReliability Assessment and from generic resources needed to meet load-plus adequacy margins.WECC believes its approach would yield the most useful information for NERC about theconsequences of high renewables penetrations in the Western Interconnection.DemandThe loads for the scenario, including the weather and economic assumptions, are based on theloads submitted for the 2007 Long-Term Reliability Assessment. This data was used since the2008 Long-Term Reliability Assessment load data was not available at the time the TEPPC studyprocess commenced. WECC does not believe that the key findings of the study werecompromised by this decision. The peak loads are based on normal weather conditions with a 50percent exceedence probability. The economic assumptions built into the load forecast werebased on submittals by the utilities. WECC does not collect these economic assumptions nordoes WECC create independent forecasts of economic conditions or loads.The base case and the Scenario Case were based on the 2007 Long-Term Reliability Assessmentloads. The difference between the scenario forecast and the 2009 Long-Term ReliabilityAssessment forecast for total WECC loads in 2017 is 7,580 MW. The primary differencebetween these two is the effect of the current recession on expectations for 2017 loads.Additionally, the demand reported in the 2009 Long-Term Reliability Assessment is a noncoincidentalpeak demand whereas the demand reported in the scenario is coincidental demand.The WECC scenario used only renewable generation to meet the scenario target, and did not relyon the various demand management programs that are allowed by the scenario definition. Ingeneral, however, WECC would not expect any of these demand side programs to be adverselyimpacted due to high renewables penetration comparable to the penetrations in the ScenarioCase. On the contrary, some of these programs — such as interruptible demand and directcontrol load management — offer significant benefits to utilities faced with the balancing andregulation problems posed by large amounts of variable generation (a prominent subset ofrenewable generation) in their BA areas. More details on demand management programs can befound in the NERC Special Report: Accommodating High Level of Variable Generation. 110GenerationA vital metric used by NERC in its reliability assessment compares resources and projected peakinternal demand. To increase the visibility and transparency of supply-side resource optionsbeing considered by Regions and subregions for this scenario assessment, NERC requiresadditional information regarding projected resources along with a comparison between theReference Case and the scenario submittals.110 http://www.nerc.com/files/IVGTF_Report_041609.pdf2009 Scenario Reliability Assessment Page 163