2009 Scenario Reliability Assessment - NERC

Scenario Reliability Self-AssessmentsOperational IssuesThe following issues are some operational considerations from this scenario assessment, andmay represent some concern depending upon the actual development of facilities.Minimum Generation Limits During Light Load ConditionsLarge additions of wind generation may present a challenge in managing the baseload generationfleet output for the day-ahead commitment. For example, system demand may fall below theminimum output of coal-fired plants. Because of the potential inverse relationship between windgeneration production and system demand, the production curve dips below the minimum outputlevels of coal-fired generation during off-peak hours (some examples are shown by the whitecircles in Figure 7 below).Figure RFC-7: Simplified Operations ExamplePotential solutions to address this issue include turning off large baseload coal plants and,instead, use gas-fired generation to meet minimum demand periods. However, most coal-firedunits have a substantial start-up time and high start-up costs. As dependence on gas increases,production costs may increase due to dispatching gas-fired generation before coal-firedgeneration. An alternative to turning off coal units is to curtail wind generation output. Minimalcosts are associated with curtailing wind. However, if the wind generator is being used to meet astate-mandated Renewable Portfolio Standard (RPS), curtailment could result in a utility fallingshort of the requirement. Furthermore, plentiful wind energy periods are often concurrent withlight-load or shoulder-peak system loading conditions, such as late evening during spring and fallseasons, such that the consequent amount of wasted wind energy is likely substantial.2009 Scenario Reliability Assessment Page 129