Comments on Issue Paper/Straw Proposal

Short-long start unit definitions update

Comment period
Jan 27, 12:00 pm - Feb 04, 05:00 pm
Submitting organizations
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Submitted 02/04/2022, 11:18 am


Jerret Fischer (

1. Comment on the initiative scope:

Salt River Project Agricultural Improvement and Power District (SRP) appreciates the opportunity to comment on the Short-Long Start Unit Definitions Update initiative.  In general, SRP supports simplifying and aligning definitions for resources in both the Tariff and Business Practice Manuals (BPMs). Correcting misalignments that currently exist between the Tariff and BPMs will provide market participants clear rules of engagement. To better understand whether the proposed changes will impact SRP’s operations, we are requesting clarification on several items in the Issue Paper:

  • Please clarify whether there are any changes to the market software.  In the initial proposal, the Real Time Market (RTM) software was stated to use a cycle time of 270 minutes to determine if a resource was startable in the RTM.  SRP requests that CAISO confirm that this is a software change from 270 minutes to 255 minutes. Should this be confirmed, SRP will request discussion with the CAISO regarding one SRP resource that may be impacted by this change.
  • Page 5 of the Issue Paper states: “However, only 255 minutes are available to perform the unit commitment process.” The rationale behind the 15 minute reduction in time between 270 minutes and 255 minutes is unclear and SRP requests further explanation.
  • SRP requests clarification on the differences between how the startup time condition (hot, warm, or cold) is used in both the Day Ahead Market (DAM) and RTM software.  SRP requests the CAISO confirm SRP’s understanding that the market software for the RTM can distinguish between hot, warm, and cold starts and choose the appropriate time when determining if the resource is startable.
  • Please clarify whether multi-stage generator (MSG) transitions are not applicable as part of the change. It is SRP’s understanding that transition times only, and not minimum up times, are considered for commitments in the RTM.  CAISO should confirm if the RTM software uses 270 minutes or 255 minutes for making these commitments.
3. Comment on the EIM governing body classification:

SRP supports the CAISO’s Joint Authority decisional classification on the basis that both the EIM and the day-ahead market will be impacted by the outcome of this initiative.  As CAISO staff noted at the January 26, 2022, initiative webinar, amending the Short Start and Long Start definitions will impact and align the definitions in the EIM and day ahead market.

4. Comment on the revised the tariff definitions of a Short Start Unit and a Long Start Unit:

SRP supports the proposed tariff definition changes but requests one clarification.  For Section 34.6, the Tariff language states, “Once per hour, near the top of each Trading Hour, immediately after the FMM and the RTUC for the same interval is completed the CAISO performs an approximately five (5) hour Short-Term Unit Commitment (STUC) run using SCUC and the CAISO Forecast of CAISO Demand over a 270-minute time horizon to commit Medium Start Units and Short Start Units, with Start-Up Times greater than the time period covered by the RTUC described in Section 34.3.”  SRP requests that CAISO address whether the term “Start-Up Times” should be changed to “Cycle Times” to reflect the time that is considered for commitment decisions.


SRP appreciates the CAISO’s consideration of these comments.

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