2009 Scenario Reliability Assessment - NERC

Scenario Reliability Self-AssessmentsNeed for Accurate Day-Ahead and Hourly Wind ForecastingPredicting, with reasonable confidence, the output level of wind generation for a future timeperiod (e.g. day ahead, hour ahead, etc.) is limited, at best. Because wind generation is driven bythe same physical phenomena as weather, the uncertainty associated with the prediction of windgeneration level at some future hour (even the next hour) may be significant. For example, inFebruary 2008 in Texas, the forecast quantity of wind generation output could not be met due toan unexpected drop in the wind. As wind generation penetration levels increase, the forecastaccuracy becomes essential to operate a reliable system. Additionally, accurate wind forecastsand timely updates are necessary in order to incorporate wind generation into the Day Aheadmarkets.The Midwest ISO uses a centralized wind forecasting program in its market footprint to capturereliability and economic aspects of integrating wind into the Day Ahead and Real Time Markets.The program uses a Multi Numerical Weather Prediction (NWP) model to come up with its bestestimate for each node, zone, Region and Midwest ISO total. PJM also is implementing anRTO-wide wind forecasting program. Also, because of the larger system size of RTOs, theoverall effects of a sudden drop in wind generation may be minimal.Need for Additional Operating ReservesContingency reserves may need to increase with large quantities of wind generation online. Thisis due to the variability of wind generation output, which may result in an inadequate amount ofcontingency reserves. This concern would dictate that the operating entity take a conservativestance, and therefore may require more contingency reserves be available in the day-aheadmarket. The variability and ramping characteristics of wind turbine output may also requireadditional spinning and contingency reserve margins, both positive and negative. The preciseamount changes day to day depending on the quality of Regional wind prevalence. These factorswould dictate that day-ahead ancillary service markets must be closely coordinated with windforecasts and real-time monitoring of wind output.Acceleration of Baseload Unit RetirementsExisting baseload generating units provide dependable operational reserve margins and reducemarket price volatility, precisely the characteristics needed in an environment striving toaccommodate large-scaled wind power integration. Many baseload units are located where theirdynamic reactive capabilities are also crucial to voltage regulation and local system reliability.However, when wind generation penetration reaches a level where many of these older and lessefficient baseload fossil-fueled units become sporadically dispatched day-in and day-out, theirowners may contemplate an accelerated retirement of these units. This accelerated retirementmay increase the need for additional operating reserves, as mentioned above.Reliability Assessment AnalysisA resource adequacy assessment of the reference and Scenario Cases would demonstrate thatRegional reliability criterion is expected to be met since the JCSP study included an assumedamount of capacity additions necessary to meet the reserve criterion as determined in studiesPage 1322009 Scenario Reliability Assessment