LOLE Report PY2024-25 Feedback

The Environmental Sector appreciates the opportunity to submit these comments on the 2024-2025 Loss of Load Expectation Report. The report states that one aspect that was “changed for this year’s study was the reduction of the available Winter unforced capacity in the PRM and LRR calculations as a result of these cold weather outages.” And at the November RASC meeting, MISO presented the final LOLE results for 2024-2025, and included in that presentation was information about adjustments MISO made that resulted in a reduction in the winter PRM percentage.  MISO states this adjustment was made based on communication with Astrape to correct for an error related to MISO’s implementation of the cold weather outage adder. 

Impact of Cold Weather Outage Adder on PRM calculation:

• The cold weather outage adder in the LOLE model increases forced outages during extreme cold weather events in the model – an important first step towards properly accounting for thermal resource limitations in the model.
• Because cold weather corresponds with high loads, and the adder increases outages, the LOL events during these cold periods tend to drive the PRMR for winter.
• MISO uses the LOLE model to ultimately determine the MISO PRM ICAP and MISO PRM UCAP.
• However, the system ICAP and UCAP values for winter do not account for the increased outage rates resulting from the cold weather adder.  
• In the November RASC meeting, MISO indicated that they had realized they missed this. To address the error, MISO said they needed to adjust the total UCAP value down during the winter LOL events related to periods where the cold weather outage adder was actively increasing forced outage rates.  (see slide 3)

We believe that the accreditation values of thermal resource classes that have a cold weather outage adder must also be reduced to reflect the added outage levels driven by the cold weather outage adder.  This is because those accreditation values (based on historic forced outage values) are the basis for the UCAP values that are inputs into the LOLE model, the same UCAP values that MISO adjusted to reduce the winter PRM.  We expect this accreditation reduction should be done on a class-wide basis, but whether this is done on a class-wide basis or unit-specific, the total accreditation of each individual class should align with the class-wide totals as assessed through the LOLE model which accounts for correlated outage risk during cold weather events using the cold weather outage adder.

This reduction in accreditation values is necessary to reflect the decreased availability modeled for these units during those cold weather LOL hours.  It is our understanding that MISO is not planning to adjust the accreditation values to account for the cold weather outage adder this year.  This is a concern because without adjusting the accreditation values along with the winter PRM, the resulting resource adequacy construct will no longer meet MISO’s 1 day in 10 standard and this raises a concern about reliability.

The cold weather outage adder is modeling the fact that there will be lower generator availability during these extreme cold weather events, but this correlated outage risk is not adequately captured in the EFORd based accreditation values.  Thus, MISO will not actually acquire enough MW of generation capacity via the PRA if it is using the current EFORd based accreditation values that do not take into account the cold weather outage adder, but is using a winter PRMR that has been reduced to adjust for this adder.

How big a problem is this? We do not know the answer to that question, and we urge MISO to do some analysis to determine the impact of this misalignment.  The November presentation shows the winter PRM for 2024-2025 was just reduced from 33.9% to 27.4%, and the PRMR was reduced by 6,710 MW.  Accreditation values need to be adjusted as well, but we don’t know by how much.  If accreditation values are also off by 6,710 MW, this would be significant. When MISO was short by about 1,230 MW of capacity in the 2022-2023 PRA, that was a reduction from a loss of load standard of 1 day in 10 year to 1 day in about 5.6 years.

Will DLOL eliminate this problem? We also do not know the answer to this question, but it will be important for MISO to evaluate whether its DLOL proposal can address this misalignment.

We request that MISO provide a public response to these questions at a future RASC meeting, and in a written form given that the next RASC meeting is not until 2024.  This could be an issue of reliability and MISO’s ability to meet load during extreme winter cold periods and if it is significant, it should be addressed expeditiously.