2009 Scenario Reliability Assessment - NERC

Regional Reliability Scenario Self-Assessmentsthe necessary ramping capacity. In addition, the curtailment of the variable generation duringthese times would likely increase.The low-load/high-variable generation poses the risk that variable generation would drop offduring off-peak when much of the flexible generation is off-line. This is the least risk toreliability and operations since there are often other generation resources available to ramp-up.However, with an increase in the level of variable generation, situations may arise where thelevel of variable and must-run generation exceeds load. As with the previous case, this situationoften coincides with periods of high hydro generation.WECC expects that a number of additional standards, guidelines, and rules would emerge fromstudies of the increase in variable generation and its impact on operations and reliability.Specifically, these would directly address the need to better forecast and control the fleet ofvariable generators in the Western Interconnection. In addition, changes to business practices andtechnologies that would enable higher levels of variable generation are anticipated. Theseinclude sub-hourly scheduling of energy and transmission, increased dynamic schedulingcapability, and the expansion of ancillary service markets.Currently, some entities in the Western Interconnection are making changes to their LargeGenerator Interconnection Agreements to address the controllability of large wind generatingstations. These include provisions that range from forecasting requirements to enabling the BA todirectly control output of the generator. 113Renewable/Variable Generation Studies in WECCA large number of variable generation - mostly wind - integration studies have been performedby entities in the Western Interconnection. Although the focus and intent of the studies are notidentical, the primary objective is the same quantify the impact of variable generation onoperations and costs. The table below outlines a subset of these studies.To facilitate a greater understanding and address of the effects of variable generation, WECC’sJoint Guidance Committee created the Variable Generation Subcommittee (VGS) in October2008. The subcommittee is made up of a broad set of stakeholders in the WesternInterconnection. The purpose of the VGS is to provide a holistic perspective of the issues andopportunities related to the presence of variable generation in the Western Interconnection. Italso serves to add value for WECC members by facilitating the development and implementationof solutions by and assuring reliability of the Western Interconnection. These challenges arebeing met through the compilation of information and member issues, coordination of issueanalysis, and dissemination of information. As a recently formed subcommittee, the VGS ismaturing. It is anticipated that the VGS would serve as the central point of facilitation for studyof renewable issues in the Western Interconnection.113 http://www.bpa.gov/corporate/WindPower/WIT.cfm,http://www.caiso.com/docs/2003/01/29/2003012914230517586.htmlPage 1702009 Scenario Reliability Assessment