Comparison of LOLP Practices

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Comparison of LOLP Practices

• Mary Johannis
• PNW Resource Adequacy Technical Committee Mtg
• January 23, 2009

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NERC Survey Results
3
NERC Survey Results
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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

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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

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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