Comparison of LOLP Practices Mary Johannis PNW Resource Adequacy Technical Committee Mtg January 23, 2009

PNW Resource Adequacy Technical Committee Meeting2 NERC Survey Results

January 23, 2009PNW Resource Adequacy Technical Committee Meeting3 NERC Survey Results

January 23, 2009PNW Resource Adequacy Technical Committee Meeting4 NERC Probabilistic Metrics Loss of Load Probability (LOLP): –The probability of load demand not met in a given hour. (Midwest Planning Reserve Sharing Group (PRSG)) –The probability that load (above a certain threshold) will not be met over a season (Northwest Power and Conservation Council); most analyses would term this an LOLE evaluation Loss of Load Expectation (LOLE): –∑ of multiple LOLP values (usually over peak hours) over a certain period of time. (Midwest PRSG) –A loss of load event is described as any single hour or group of consecutive hours where load exceeds available resources. For example, 1 hour alone of unserved energy constitutes a LOLE just as 5 consecutive hours of unserved energy constitutes an LOLE. (ERCOT) Expected Unserved Energy (EUE): –∑ of hourly curtailments across all iterations of the stochastic simulation (ERCOT), expressed as average MWHs over 10 years

January 23, 2009PNW Resource Adequacy Technical Committee Meeting5 NERC Possible Common Methods Curtailments Measured –LOLP can be measured at the peak hour for 260 days (excluding weekends), for 360 days, over all hours of a season, over all 8760 hours in a year –LOLE is ∑ of LOLP over time –EUE is typically synonymous with Energy Not Served [ENS], measured in MWh, across all iterations of the stochastic simulation What is a Loss of Load (LOL) Occurrence? –Single instance in ability to serve firm load Sometimes the LOL occurrence also includes operating reserves Methodology may allow activation of Emergency Operating Procedures to avoid LOL occurrence –∑ of curtailments over period. In Northwest, season is not counted as an LOL occurrence unless curtailment is above minimum energy or capacity threshold

January 23, 2009PNW Resource Adequacy Technical Committee Meeting6 NERC Survey Conclusions Good reasons for different analyses: –Resource mix: e.g. large amounts of energy- limited resources dictate different analysis than in a capacity constrained system –Transmission limitations: deliverability needs to be considered if system with significant congestion –Lack of fuel diversity: evaluate whether fuel transportation/ storage is a reliability issue Does LOLE target of 0.1 day imply the same level of reliability for all Regions? Need to speak a common language  Definition of Best Practices for Resource Adequacy Assessment