2009 Scenario Reliability Assessment - NERC

Scenario Reliability Self-AssessmentsWECCIntroduction and SummaryThe Western Electricity Coordinating Council (WECC) studied the effect of one scenario of 15percent renewables generation (by energy) in the Western Interconnection in 2017. The scenariothat was studied was not the only one that could have been constructed and other scenarios couldlead to different specific results. The study, however, along with other efforts underway inWECC did lead to several general overall conclusions.1. High levels of renewable generation, because of their spatial location relative to Westernload centers, can lead to stresses on the capacity of the transmission system and the needto increase that capacity to deliver the generation to load.2. High levels of variable renewable generation can raise significant operating challengesthat can require new institutional arrangements and business practices in order toeconomically maintain the ability of Balancing Authorities (BA) to meet North AmericanElectric Reliability Corporation (NERC) and WECC reliability standards.3. While high levels of renewable generation per se do not raise adequacy issues, highlevels of variable renewable generation, raise two kinds of adequacy issues.o First, it is important to evaluate how much variable generation can reliably beexpected to contribute to system peak.o Second, high penetrations of variable generation can require significant amountsof flexible resources to integrate that variable generation into the grid. Onlyresources with the ability to ramp up and down quickly — such as hydro,combustion turbines, storage resources, and certain demand-side managementresources — have the appropriate attributes to be able to integrate wind, solarphotovoltaic, and other variable renewable resources into the grid.4. High levels of renewable generation, typically with very low operating costs, would havea significant effect on generation and fuel use by those units typically on the margin (i.e.,gas generation) in the Western Interconnection. This could raise issues of gasprocurement and scheduling, though WECC was unable to study those issues. Natural gassupplies delivered through intra-state pipeline systems offer the greatest operatingflexibility when such systems are connected to gas storage projects. The areas in WECCthat plan to follow variable renewable output with gas-fired generation otherwise mayneed to have natural gas storage infrastructure built or inter-state pipelines would have toaccept day-after or real-time schedule changes.WECC and its members (utilities, state and provincial entities, independent generators, andothers) are addressing the issues raised by these conclusions.WECC has an extensive study program ongoing under the guidance of the TransmissionExpansion Planning Policy Committee (TEPPC). This work is performed in coordinationwith Western Subregional Planning Groups (SPG) and individual transmission providersto evaluate long-range needs for transmission expansion in the Western Interconnection.The coordination among the three levels of study efforts, interconnection-wide to2009 Scenario Reliability Assessment Page 149