2009 Scenario Reliability Assessment - NERC

Scenario Reliability Self-AssessmentsBecause of the potential inverse relation between wind production and demand, the productioncurve begins to dip below the coal minimum output levels during off-peak hours. Potentialsolutions to address this issue include:Shut down baseload coal plants and increase gas utilization. Most coal units have asubstantial start-up time and high start-up costs. As dependence on gas increases,production costs would increase by using gas over coal.Curtail wind generation outputs. Minimal costs are associated with curtailing wind.However, if the asset is being used to meet a State RPS, curtailment could result in autility falling short of the requirement. Furthermore, plentiful wind energy periods areoften concurrent with light-load or shoulder-peak system loading conditions, such as lateevening during Spring and Fall, such that the consequent amount of unused wind energyis likely substantial.(b) Ramp Requirements and Out-of-Phase RampingRamp is the increase or decrease of generation required to meet changes in load and windgeneration across an hour. Wind generation ramps can have an inverse correlation to daily loadramps resulting in the need for additional reserves to support ramp. As more wind generation isadded to the system, the magnitude and direction of ramping requirements are expected toincrease. Figures MRO-6 and MRO-7 use the real-time actual system information from the 2008peak week (July 27, 2008 through August 2, 2008) to display the relationship between windgeneration levels and their corresponding ramp characteristics.Figure MRO-6: July 27, 2008 – August 2, 2008 MRO-US Real-Time Ramp Requirement15,00050,000RT Wind Output and Ramp Requirements(MW)10,0005,0000-5,00040,00030,00020,00010,0000Demand (MW)-10,000-10,0007/27/08 7/28/08 7/29/08 7/30/08 7/31/08 8/1/0 8/2/08 8/3/08Hourly Ramp Requirement2008 Peak Demand2008 RT Peak Wind Output2009 Scenario Reliability Assessment Page 47