Comments on Issue paper and Straw Proposal and May 9 working group meeting

1. Please provide a summary of your organization’s comments on the Issue Paper & Straw Proposal on Outage Management, Nonlinearity, & SOC Clarification and May 9, 2025 meeting discussion:

The California Community Choice Association (CalCCA) appreciates the opportunity to comment on the Storage Design and Modeling Issue Paper and Straw Proposal. In summary, these comments recommend that the CAISO:  

• Evolve its Outage Management System (OMS) to align with storage-specific outage types and characteristics;  

• Revise its proposed path forward for representing nonlinearity to implement a Master File parameter expeditiously, and in the interim, direct storage resources to use the “Technical Limitations Not in the Market Model” outage card; and 

• Explore the state-of-charge (SOC) definition to ensure accurate representation of unit capabilities.  

2. Please provide your organization’s comments on Outage Management Enhancements:

CalCCA supports the CAISO’s straw proposal to evolve its OMS to align with storage-specific outage types. Resources participating in the CAISO markets should be able to accurately represent their availability to the CAISO. There is currently a lack of clarity around how best to do so for storage resources using the existing OMS functionality. For these reasons, the CAISO should move forward with its straw proposal to assess how to enhance OMS to better reflect storage availability. 

3. Please provide your organization’s comments on Representation of Nonlinearity:

The CAISO should revise its proposed path forward for representing nonlinearity, implement a Master File parameter expeditiously, and in the interim, direct storage resources to use the “Technical Limitations Not in the Market Model” outage card. The Issue Paper and Straw Proposal explains that lithium-ion battery storage systems exhibit nonlinearity, in which their charging and discharging capabilities change as they approach their SOC limits at rates that are not easily predictable.[1] Ahead of summer 2025, the CAISO proposes to use the “Plant Trouble” nature of work outage card, a resource adequacy availability incentive mechanism (RAAIM) applicable outage card. When these outage cards are used for nonlinearity, the CAISO proposes the resource include a note in the outage card to state that the outage is related to nonlinearity. Longer term, the CAISO indicates that integrating resource-specific values into the Master File is the “most desirable and lasting” alternative.[2]

CalCCA agrees that a Master File parameter is the best way to reflect nonlinearity. The CAISO should, as the preferred and most durable approach, seek to expeditiously implement a Master File parameter. In the interim, however, the CAISO will need to provide clarity around which outage card storage resources should use to reflect non-linearity. The CAISO should not rely on the “Plant Trouble” outage card, which is RAAIM-applicable and does not accurately describe the reason for the outage. Nonlinearity is a fundamental characteristic of the resource, not always an issue of unavoidable outage. Nonlinearity for storage resources is comparable to the operational characteristics of multi-stage generating (MSG) resources. Like MSG resources, which have multiple operating configurations and only one such configuration can be operated in any one interval, storage resources can have different operating characteristics that they operate under depending on their state-of-charge. The CAISO’s longer-term solution is aligned with how MSG operating configurations are reflected.  The “Plant Trouble” outage card, on the other hand, is used when “plant equipment fails or is in danger of imminent failure resulting in curtailment of dispatchable capacity.”[3] When an outage truly reflects the definition of “Plant Trouble,” RAAIM application (or unforced capacity application) should apply to provide resources with incentives to perform planned maintenance to avoid equipment failures and improve the reliability of the resource. Nonlinearity does not fall within this definition, however.

Instead, the CAISO should apply the “Technical Limitations Not in the Market Model” outage card to reflect nonlinearity in the interim. This outage card is used when to “provide notification that resource is unavailable due to technical limitations not captured in the CAISO market model and that result in infeasible dispatches because they are inconsistent with the resource’s design capabilities.”[4] This definition better reflects the reason for submitting an outage card in cases of nonlinearity. The CAISO’s ultimate goal is to modify the market model to adequately reflect non-linearity through the Master File. It would be contradictory to apply RAAIM to non-linearity in the interim, when the long-term solution is to reflect this characteristic in the market model. The CAISO should specify that storage resource non-linearity should be reflected through the “technical limitations not in the market model” outage type, which is RAAIM exempt, until a Master File parameter can be implemented to reflect these characteristics. If the CAISO is concerned that this outage card will be used inappropriately to avoid RAAIM when the resource is not experiencing nonlinearity constraints, the CAISO should work with owners/operators of storage resources and the Department of Market Monitoring to define clearly when resources can use this outage to address nonlinearity. 

[1]           See Issue Paper and Straw Proposal, at 9.

[2]          Id., at 12.

[3]         CAISO, Business Practice Manual for Outage Management, Version 30 (July 27, 2023), at 22.

 [4]         Ibid.

4. Please provide your organization’s comments on SOC Clarification:

CalCCA supports the CAISO’s plan to explore SOC in this initiative to ensure SOC accurately represents each units’ capabilities. In the Issue Paper and Straw Proposal, the CAISO discusses the need to further clarify the expectations related to the energy available from storage devices. The CAISO also introduces the term “inaccessible energy,” in which “a resource appears to have available energy based on its telemetered SOC,” but “underlying limitations could prevent it from fully adhering to dispatch instructions.”[1] It would be helpful for this initiative to clarify the definition of SOC and its relationship to energy availability. CalCCA generally agrees with California Energy Storage Alliance that what CAISO defines as inaccessible “is in fact accessible, but at different operational parameters and with costs not currently reflected in the market.”[2] Alignment regarding SOC expectations is a worthwhile objective for this initiative.

[1]           Issue Paper and Straw Proposal, at 13.

[2]           Id., at 15.

5. Please provide any additional comments:

CalCCA has no additional comments at this time.  

1. Please provide a summary of your organization’s comments on the Issue Paper & Straw Proposal on Outage Management, Nonlinearity, & SOC Clarification and May 9, 2025 meeting discussion:

Comments on Storage Design and Modeling

Issue Paper and Straw Proposal on Outage Management,

Nonlinearity, and SOC Clarification

Department of Market Monitoring

May 23, 2025

Overview

The Department of Market Monitoring (DMM) appreciates the opportunity to comment on the Storage Design and Modeling Issue Paper and Straw Proposal on Outage Management, Nonlinearity, and SOC Clarification and the corresponding stakeholder meeting held May 9, 2025.[1]^,[2] In these comments, DMM adds to our previous comments from the ISO’s Storage Design and Modeling (SDM) Working Group 1 through 3.[3],[4]

While DMM supports many items in the proposed scope of this initiative, DMM continues to encourage the ISO to address the storage bid cost recovery (BCR) concerns as a top priority, before undertaking additional storage design enhancements that may considerably slow the pace of development for needed storage bid cost recovery enhancements.

In these comments, DMM addresses the following three issues raised in the Issue Paper and Straw Proposal:

• Modeling nonlinearity of storage operations. DMM supports development of market model improvements that incorporate nonlinearities of storage resource operations. If the ISO is unable to directly model nonlinearities in the near term, DMM conditionally supports extending dynamic limit functionality to storage resources as an interim solution. If the ISO extends dynamic limit functionality to all storage resources, the ISO should also:
  • Clearly specify the acceptable use of dynamic limits for storage resources in the CAISO Tariff,
  • Require new Master File data sufficient to allow monitoring of the use of the dynamic limits, and
  • Establish that resources using the dynamic limit would be ineligible for real-time bid cost recovery (BCR) for intervals in which the dynamic limit impacts the resource’s dispatch – up to the entire operating day if it is infeasible to accurately identify such intervals.
• Outage reporting. DMM supports improvements to outage reporting that better reflect limitations unique to storage resources. DMM continues to recommend ISO staff work together to coordinate the development of new storage outage types into resource adequacy policy developments.

• SOC definition and calculation. DMM supports improvements to the definition of SOC to clearly reflect resources’ stored energy that is available to the market.

Comments

DMM conditionally supports extending the use of dynamic limits to storage resources

Stakeholders have suggested implementing dynamic limits for all storage resources to allow scheduling coordinators to manage issues such as foldback. DMM has previously recommended against this use of dynamic limits.[5] However, the ISO has indicated it cannot model the foldback limitations in the near-term. As a result, DMM conditionally supports the use of dynamic limits as an interim solution.[6]

DMM’s conditional support for the use of dynamic limits by storage resources depends upon the ability of the ISO and DMM to monitor for appropriate use, clearly enforceable tariff provisions in the event of inappropriate use, and ineligibility of real-time bid cost recovery when dynamic limits impact the resource’s dispatch.

If this interim solution is pursued, DMM requests improvements to Master File to facilitate monitoring of dynamic limit usage for all storage resources. DMM also requests the ISO detail the appropriate use of dynamic limits for storage resources to manage foldback and nonlinearities in the CAISO Tariff.  Finally, DMM requests that resources using the dynamic limit would be ineligible for real-time BCR for intervals in which the dynamic limit impacts the resource’s dispatch. This would include the interval in which the dynamic limit was used directly, as well as any surrounding intervals at other points in the day where the use of a dynamic limit in a previous or future interval may have impacted the resource’s availability. If it is deemed infeasible to identify such intervals, the ISO should establish that resources would be ineligible for real-time BCR for the entire operating day in which a dynamic limit is used. 

The ISO developed dynamic limits for hybrid resources because the market model does not incorporate all the information of the individual component generating units of a hybrid resource. The dynamic limit is intended to allow resources to capture constraints and operational limitations that may not be modeled, to aid in a feasible dispatch.

Foldback is similar, in that it creates an operational limitation in the upper and lower ends of the storage resource’s state-of-charge (SOC). To overcome the nonlinearities of battery storage charging and foldback, in the interim, the ISO could extend the dynamic limit functionality to storage resources.

DMM believes that with appropriate transparency, monitoring, and bid cost recovery rules, this could be an improvement over the status quo, but DMM does not see this as a long-term solution. More robust modeling of nonlinearities and other storage limitations through, e.g., SOC based bidding, may be preferred instead as a long-term approach.[7],[8]

To facilitate monitoring, DMM requests the ISO collect in Master File the operational characteristics for each storage resource related to foldback. The Master File detail could include the expected upper and lower regions of the SOC where foldback would become an operational limitation to the resource, and the expected modified ramp rate the resource would experience during foldback.

A consideration discussed below is the use of outage cards and their interaction with the Resource Adequacy Availability Incentive Mechanism (RAAIM), and forthcoming unforced capacity (UCAP) methodology for resource adequacy capacity accreditation. These policies are used to create incentives for resources’ operational and planning availability to the market. Because dynamic limits were developed for hybrid resources, which are exempt from RAAIM, there has been no discussion of the RAAIM implications of dynamic limit use. 

However, DMM believes the dynamic limit may impact RAAIM calculations for storage resources in a manner similar to outages, because dynamic limits adjust real-time bids to the availability of the resource reflected by the dynamic limit. This potential interaction could help incentivize resources to be available during stressed grid conditions. The dynamic limit would not impact UCAP calculations because the dynamic limit does not reflect a physical outage (or derate) on the resource reported through the outage management system (OMS).

DMM conditionally supports extending the dynamic limit functionality to storage resources to reflect foldback and nonlinearities. To the extent dynamic limit use can have RAAIM implications, storage resources will still be incentivized through RAAIM to demonstrate their maximum available capacity. In the long term, DMM recommends the ISO sunset this feature, develop market functionality to allow storage resources to bid SOC to manage issues of foldback, and develop other market enhancements as necessary to manage other operational nonlinearities.[9]

DMM supports improved outage reporting for storage resources

DMM continues to support enhancements to storage outage reporting for storage resources.[10] Storage resources face limitations and outage types not currently covered in outage management system (OMS) that are unique to storage resources, such as negative Pmin and energy (SOC) limitations.

DMM understands that outages may be one approach currently used to manage foldback issues discussed above. Should outages continue to play a role in managing foldback, DMM recommends introduction of a new outage card type to signal effects of foldback on ramp rates. However, DMM agrees with California Public Utilities Commission Energy Division staff that outages used to communicate foldback should not be RAAIM exempt. RAAIM exemption would not send the appropriate incentives to contracted capacity to perform to their RA obligations.[11]

DMM further supports the development of additional outage types that are unique to storage resources, and incorporating the cause descriptions in the Business Practice Manual nature of work table for storage resources. Outages are physical limitations of a resource, and these physical limitations should be detailed for storage scheduling coordinators to reflect resource availability to the market. Improved outage reporting will assist market operators and monitors in ensuring the system is operating reliably and efficiently. DMM continues to recommend ISO staff work together to coordinate the development of new storage outage types into resource adequacy policy developments.[12]

Instances of observed lack of availability highlight the need to improve SOC definition

DMM has raised concerns to the ISO about the definition and calculation of SOC. The concerns arise from instances of observed lack of availability of storage resources, and a vague tariff definition of what SOC should represent. The definition specifies that SOC should reflect stored energy available to the CAISO markets, but does not provide a definition of availability, e.g., within what timeframe the stored energy must be available.[13]

Clarifications to the definition and calculation of telemetered SOC need to more accurately reflect the true SOC availability of storage resources to the market, at the time of market dispatch. DMM has identified cases in which the SOC is greater than zero, but the stored energy is unavailable to the market. This situation is most apparent in cases where the resource is available and receiving a dispatch operating target, however the resource cannot respond to the dispatch because the telemetered SOC is unavailable, which is later revealed through an outage. This leads to the market solving under inaccurate conditions for these resources. DMM recommends the ISO clarify a definition of SOC availability in the tariff, and consider including a standardized approach to calculating SOC.

[1] Storage Design and Modeling Issue Paper and Straw Proposal on Outage Management, Nonlinearity, and SOC Clarification, California ISO, March 27, 2025: https://stakeholdercenter.caiso.com/InitiativeDocuments/2025-03-27-SDM-Outage-Management-Nonlinearity-SOC-Definition-Issue-Paper-Straw-Proposal-FINAL.pdf

[2] Storage Design and Modeling Working Group: Outage Management, Nonlinearity, and SOC Clarification, California ISO, May 9, 2025: https://stakeholdercenter.caiso.com/InitiativeDocuments/Presentation-StorageDesignandModeling-May9-2025.pdf

[3] Comments on Storage Design and Modeling Working Group Session 1, Department of Market Monitoring, January 8, 2025: https://www.caiso.com/documents/dmm-comments-on-storage-design-and-modeling-working-group-session-dec-11-2024-jan-8-2025.pdf

[4] Comments on Storage Design and Modeling Working Group Session 2 and 3, Department of Market Monitoring, March 7, 2025: https://www.caiso.com/documents/dmm-comments-on-storage-design-and-modeling-working-group-sessions-2-and-3-mar-07-2025.pdf

[5] Ibid.

[6] Storage Design and Modeling Working Group: Outage Management, Nonlinearity, and SOC Clarification, California ISO, May 9, 2025: https://youtu.be/4DPKVa7skik

[7] Comments on Storage Design and Modeling Working Group Session 1, Department of Market Monitoring, January 8, 2025: https://www.caiso.com/documents/dmm-comments-on-storage-design-and-modeling-working-group-session-dec-11-2024-jan-8-2025.pdf

[8] Comments on Storage Design and Modeling Working Group Session 2 and 3, Department of Market Monitoring, March 7, 2025: https://www.caiso.com/documents/dmm-comments-on-storage-design-and-modeling-working-group-sessions-2-and-3-mar-07-2025.pdf

[9] Comments on Storage Design and Modeling Working Group Session 2 and 3, Department of Market Monitoring, March 7, 2025: https://www.caiso.com/documents/dmm-comments-on-storage-design-and-modeling-working-group-sessions-2-and-3-mar-07-2025.pdf

[10] Ibid.

[11] Storage Design and Modeling Issue Paper and Straw Proposal on Outage Management, Nonlinearity, and SOC Clarification, California ISO, March 27, 2025: https://stakeholdercenter.caiso.com/InitiativeDocuments/2025-03-27-SDM-Outage-Management-Nonlinearity-SOC-Definition-Issue-Paper-Straw-Proposal-FINAL.pdf

[12] Ibid.

[13] CAISO Tariff – Appendix A, California ISO, February 5, 2025: https://www.caiso.com/documents/appendix-a-master-definition-supplement-as-of-feb-5-2025.pdf

2. Please provide your organization’s comments on Outage Management Enhancements:

Please see the PDF attached below the final question for DMM's fully formatted complete set of comments. For the reader's convenience, the complete text of the comments is pasted in response to #1, but there may be some formatting errors.

3. Please provide your organization’s comments on Representation of Nonlinearity:

Please see the PDF attached below the final question for DMM's fully formatted complete set of comments. For the reader's convenience, the complete text of the comments is pasted in response to #1, but there may be some formatting errors.

4. Please provide your organization’s comments on SOC Clarification:

Please see the PDF attached below the final question for DMM's fully formatted complete set of comments. For the reader's convenience, the complete text of the comments is pasted in response to #1, but there may be some formatting errors.

5. Please provide any additional comments:

Please see the PDF attached below the final question for DMM's fully formatted complete set of comments. For the reader's convenience, the complete text of the comments is pasted in response to #1, but there may be some formatting errors.

1. Please provide a summary of your organization’s comments on the Issue Paper & Straw Proposal on Outage Management, Nonlinearity, & SOC Clarification and May 9, 2025 meeting discussion:

The Public Advocates Office at the California Public Utilities Commission (Cal Advocates) appreciates the opportunity to comment on the May 9, 2025 meeting and the Issue Paper and Straw Proposal on Outage Management, Nonlinearity, and SOC Clarification.[1]

Please see Cal Advocates’ responses to questions 3 and 4.

[1] CAISO, Storage Modeling and Design Issue Paper and Straw Proposal on Outage Management, Nonlinearity, and SOC Clarification, March 27, 2025 (Straw Proposal).

2. Please provide your organization’s comments on Outage Management Enhancements:

Cal Advocates does not have comments at this time.

3. Please provide your organization’s comments on Representation of Nonlinearity:

Cal Advocates supports the California Independent System Operator Corporation’s (CAISO) proposal to maintain the Resource Adequacy Availability Incentive Mechanism (RAAIM)[1] penalties for storage resources that use outage cards to indicate unavailable capacity due to storage foldback[2] at high and low state-of-charge (SOC) levels.[3]  CAISO has identified that RAAIM penalty exemptions already decrease RAAIM’s effectiveness,[4] and potentially harm grid reliability. RAAIM is CAISO’s primary tool to enforce Resource Adequacy (RA) must offer obligations.  RAAIM penalties for storage resources may provide incentives for existing and new resources to consider energy capacity augmentation or other solutions to mitigate the negative impact of foldback and unavailable RA capacity on grid reliability.[5]  

However, RAAIM may not be sufficient on its own to ensure that storage operators bid foldback-limited RA capacity into the market.  RAAIM may also not provide sufficient incentives for resource owners to invest in innovative solutions to mitigate foldback’s negative impact on grid reliability.[6]  As such, CAISO should pursue modifications to the CAISO Master File to incorporate electrical current limits at different SOC levels, as well as enhancements to the market participation model for storage to include a biddable SOC parameter.  These modifications and enhancements would help to ensure that energy storage resources will be available to meet their RA must-offer obligations.[7]

[1] CAISO uses RAAIM to penalize and incentivize RA resources to be available to the CAISO day-ahead and real-time markets.  “RAAIM defines a standard for evaluating performance of RA resources and creates incentives and non-availability charges for RA resources.”  CAISO, Resource Adequacy Working Group Revised Discussion Paper & Final Recommendation Plan: Version 3, July 26, 2024 (RAMPD July Discussion Paper) at 16-17.  Available at: https://stakeholdercenter.caiso.com/InitiativeDocuments/Revised-Discussion-Paper-and-Final-Recommendation-Plan-Resource-Adequacy-Modeling-and-Program-Design-Working-Group-Jul-26-2024.pdf.

[2] Storage foldback in lithium-ion batteries refers to automatic battery management system (BMS) control algorithms that actively manage electrical current to ensure safe and optimal operation at high and low SOC levels.  Foldback decreases battery maximum power discharge capacity at low SOC and decreases maximum charging capacity at high SOC.

[3] Straw Proposal at 12.

[4] CAISO, Resource Adequacy: Issue Paper, November 7, 2024 at 65.  Available at: https://stakeholdercenter.caiso.com/InitiativeDocuments/Issue-Paper-Resource-Adequacy-Modeling-and-Program-Design-Nov-07-2024.pdf.

[5] Cal Advocates notes that CAISO has determined that the current design of RAAIM may be ineffective at incentivizing resource availability. CAISO is currently considering a replacement mechanism, which does not provide exemptions, in CAISO’s Resource Adequacy Modeling and Design initiative.  CAISO, RA Modeling & Program Design: Modeling Improvements + Straw Proposal Leanings and Options, February 11, 2025 at 31.  Available at: https://stakeholdercenter.caiso.com/InitiativeDocuments/Presentation-Resource-Adequacy-Modeling-and-Program-Design-Feb-11-2025.pdf.

[6] RAMPD July Discussion Paper at 14.

[7] RA resources have must-offer obligations to be available to CAISO for dispatch.  CAISO Tariff 40.6.

4. Please provide your organization’s comments on SOC Clarification:

Cal Advocates agrees with CAISO that the use of outage cards to in effect, dynamically modify the technical minimum and maximum capacity limits of storage resources specified in the CAISO Master File is an improper use of the outage management system (OMS).[1]  The technical information in the CAISO Master File should be as accurate as possible to provide greater assurance that real-time awards do not result in infeasible energy schedules that negatively impact system reliability.

Cal Advocates also agrees with CAISO that integrating electrical current rates at different SOC levels in the CAISO Master File is a longer-term durable solution for accurate modeling of energy storage capacity.[2]  Market efficiency would be further improved if CAISO also adopts an Energy Storage Resource (ESG) model with a biddable SOC parameter.

[1] Straw Proposal at 14.

[2] Straw Proposal at 12.

5. Please provide any additional comments:

 Cal Advocates has no further comments at this time.

1. Please provide a summary of your organization’s comments on the Issue Paper & Straw Proposal on Outage Management, Nonlinearity, & SOC Clarification and May 9, 2025 meeting discussion:

The California Energy Storage Alliance (CESA) appreciates the opportunity to comment on the Issue Paper & Straw Proposal on Outage Management, Nonlinearity, & SOC Clarification.  CESA is supportive addressing items that can be quickly implemented.  

2. Please provide your organization’s comments on Outage Management Enhancements:

CESA is supportive of the proposed OMS enhancements: 

• Support overlapping outage cards that can adjust Availability, Load Max, Max Energy and Min Energy values on one card
• Allowing non-NULL values in addition to NULL for other cards (as related to ancillary services [AS])
• Creating a single Out-of-Service checkbox for Non-Generator Resources (NGRs)
• Allowing for Load Max (Pmin) rerates on Test Energy cards during New Resource Implementation 

CESA understands the need to delay allowing automatic acceptance of updates to forced outage cards given implementation priorities.  While storage operators have submitted this request in this stakeholder effort, other market participants have similarly raised concerns with challenges with the manual approvals for forced outage updates. CESA requests CAISO reevaluated the feasibility of implementing automatic approvals of forced outage updates for all resources instead of only storage.^[1]   However, CESA requests that CAISO provide an estimate for when this enhancement could be implemented.  For example, could automatic acceptance be included in the Fall 2025 release?

[1] At the stakeholder call, CAISO explained the lift was medium to high because they thought it would require a new Nature of Work card it would require specific to storage resources that would allow CAISO to differentiate between this outage requests modeled for NGRs that may need automatic approval versus other resources that do need automatic approval. This is overly complex and unnecessary as all resources are negatively impacted and all forced outage updates should be automatically approved.

3. Please provide your organization’s comments on Representation of Nonlinearity:

CESA supports using outage cards to reflect non-linearity prior to Summer 2025.  Integrating current rates as resource specific values in the Master File or developing a biddable SOC market model can be discussed in later phases of this initiative.

CESA recommends the CAISO Technical Limitations not in Market Model NOW be utilized to reflect nonlinearity.  Importantly, this NOW is exempt from the Resource Adequacy Availability Incentive Mechanism (RAAIM), meaning that the unavailability of a resource under this NOW will not be counted against its availability performance and would therefore not be subject to potential applicable charges for that outage period. 

The accurate modeling of nonlinearity would result in the market dispatching the resource consistent with the storage resources operational characteristics.  Absent the need to use outage card, the storage resource would not be subject to RAAIM.  The market already accurately recognizes similar thermal resource dispatch limitations. The thermal resource model recognizes that the full Pmax of the resource is not immediately available (ramp limitations).  As the graph below shows, the thermal resource and the storage resource provide similar energy over the four-hour duration. However, the thermal resource would not be subject to RAAIM for its comparable dispatch limitation early in the 4-hour period, while the energy storage resource is subject to RAAIM for its comparable dispatch limitation at the end of the 4-hour period.

Similarly, the CAISO rules allow special consideration for forbidden operating regions (FOR) for thermal generators. A Generating Unit may be scheduled or dispatched within a FOR in an interval only if it takes longer than the duration of the interval to cross that region. In such a case, the Generating Unit must be scheduled or dispatched in subsequent intervals in the same direction (up or down) so that it clears the FOR in the least number of intervals possible. Depending on its Crossing Time, a resource may be dispatched to the boundary of its FOR before proceeding to cross the FOR in subsequent intervals. When thermal units pass through FOR, they are not required to submit an outage card. In addition to FOR, CAISO systems have special considerations for multi-stage generators, which have specific crossing times between two configurations, and those crossing times have ramp rates that are different from those of other configurations. CAISO rules do not require MSG units to submit outages when MSG transitions between two configurations. 

It is unfair to require storage resources to utilize a NOW that would result in RAAIM penalties as an interim solution since nonlinearity cannot be accurately modeled at this time.  A similar limitation to thermal resources is not assessed RAAIM because the limitation is modeled. Thus, the appropriate card for storage until the market can model its current rates is a RAAIM exempt card so it is treated fairly relative to thermal assets.

4. Please provide your organization’s comments on SOC Clarification:

CESA supports expanding the Direct Telemetry BPM to clarify that the instantaneous SOC and the maximum continuous energy limit should represent the amounts that are available to the CAISO at the time these values are conveyed through telemetry. The value should represent the amount available to the CAISO for either market dispatches or exceptional dispatches. For example, a storage resource may have Master File registered values for minimum continuous energy limit and maximum continuous energy limit of 0 MWh and 45 MWh respectively. The resource can reflect an unwillingness to discharge below 5 MWh or charge above 40 MWh through the market biddable parameters for the Lower State of Charge Limit and the Upper State of Charge Limit indicating what is available to the market. The CAISO grid operators would still be able to issue exceptional dispatches (ED) down to 0 MWh or up to 45 MWh. Consequently, it is critical that the values telemetered are for the operating limits for storage that can be used for both market instructions or exceptional dispatches. Otherwise, the CAISO grid operators may not see sufficient telemetry to support the ED.

5. Please provide any additional comments:

No additional comment. 

1. Please provide a summary of your organization’s comments on the Issue Paper & Straw Proposal on Outage Management, Nonlinearity, & SOC Clarification and May 9, 2025 meeting discussion:

The issue paper and meeting described CAISO’s highest priorities with respect to new work on storage (in particular, its concern with accurate representation in the market processes of available battery energy), and also describes its assessment of stakeholder priorities (which emphasize the need to enhance the Outage Management System for battery needs, and the significance of foldback limitations).  PG&E believes both descriptions were useful and largely accurate, and agrees with the prioritizing of OMS enhancements, but believes understanding of CAISO’s plans beyond its immediate priorities would be greatly aided by the provision of information about the CAISO resources expected to be available for the most urgent work (i.e., whether resources for OMS enhancements can be utilized independent of the DAME/EDAM implementation), and by the provision of a longer-term timeline for the initiative including all elements CAISO believes are included in this initiative’s scope. 

2. Please provide your organization’s comments on Outage Management Enhancements:

PG&E agrees that the most immediate need expressed by storage operators is for improvements to the Outage Management system, both in terms of ease of use and in its ability to correctly communicate battery status to CAISO operations.  PG&E also believes (though CAISO has not explicitly stated) that work on the OMS system can proceed in parallel with the higher priority rollout of DAME and EDAM. 

PG&E supports use of an outage card in OMS to capture foldback limitations in the near term.  It is to be expected that such outage cards will be automatically and immediately accepted for use in the market systems, and that OMS enhancements will make modifications and removals of these cards as easy as possible for battery operators.  PG&E believes changes to the battery storage market model are required to capture foldback limitations in the long term, and supports beginning work on market model changes as soon as possible after DAME/EDAM implementation. 

3. Please provide your organization’s comments on Representation of Nonlinearity:

PG&E believes the determination of whether foldback restrictions should or should not affect battery RA capacity and UCAP calculations requires agreement between CAISO and the CPUC, including a draft proposal process allowing stakeholder comment. 

PG&E has no objections to SCE’s proposal to incorporate information about foldback into the Master File as long as those limitations are based on physical attributes of the storage resource that can be documented/defended. We also stress that such information cannot be used by market processes without significant modeling changes that should require stakeholdering and market simulation at a minimum. 

4. Please provide your organization’s comments on SOC Clarification:

PG&E supports CAISO’s move to require that SOC as seen by market processes represent SOC available to the market, allowing for some transitional process to support battery operators who currently base SOC telemetry on raw voltage data. 

The term “available” needs to be clarified; our understanding is that “available” means that this energy is available to the market without restriction. 

5. Please provide any additional comments:

PG&E acknowledges the urgency of implementing the modified SOC constraint to enforce flexible ramp up deliverability.   

PG&E requests monitoring and provision of market data as to whether the near-term solution solves the operational issue, whether it excessively constrains real-time battery participation in the energy, AS and flexible ramping product markets, whether the constraint change interacts with the ASSOC constraint in such a way as to further reduce battery bid cost recovery, and whether similar deliverability problems arise with respect to flexible ramp down under some circumstances.   

Also, after DAME implementation PG&E requests that CAISO determine whether the modified calculation improves or adversely affects the issue of day ahead imbalance reserve clawback in real time. 

Finally, given that CAISO has “shown its hand” in making the assertion that its storage-bid model will fully resolve the foldback issue, PG&E requests that a discussion of the current status of this solution be made part of the near-term stakeholder process.  Even if nothing has changed from the CAISO’s previous presentations to stakeholders and to FERC, a reiteration of that status quo ante will clarify what CAISO believes is possible in this realm. 

1. Please provide a summary of your organization’s comments on the Issue Paper & Straw Proposal on Outage Management, Nonlinearity, & SOC Clarification and May 9, 2025 meeting discussion:

PGE appreciates efforts by CAISO stakeholders and staff to explore storage enhancements, especially as BESS resource buildout continues across the region. PGE is interested in leveraging these improvements as PGE expands BESS participation.

2. Please provide your organization’s comments on Outage Management Enhancements:

PGE is interested in OMS enhancements as part of a suite of tools to allow market participants dynamic participation of BESS units. 

3. Please provide your organization’s comments on Representation of Nonlinearity:

PGE is supportive of improvements to represent non-linearity characteristics of BESS. However, PGE would like additional discussions on the use of outage cards and master file integration solutions as short term and longer-term solutions, respectively. 

Incorporating the foldback characteristics of BESS resources within the CAISO master file could be re-used among distinct market participants with identical yet distinctly owned or contracted BESS resources. 

4. Please provide your organization’s comments on SOC Clarification:

PGE agrees with participant requests for additional policy learning regarding storage rules across other energy markets, given the novelty of BESS market participation. PGE strongly supports design development to protect BESS resources in low-SOC scenarios from the physical risks associated with full discharging. 

5. Please provide any additional comments:

PGE appreciates the CAISO’s end-of-hour SOC walkthrough, including explanation of end-of-hour parameters and the operational impacts of different bidding practices. To the extent possible, PGE appreciates further learning opportunities as BESS resource participation increases across CAISO markets. 

1. Please provide a summary of your organization’s comments on the Issue Paper & Straw Proposal on Outage Management, Nonlinearity, & SOC Clarification and May 9, 2025 meeting discussion:

REV Renewables (REV) appreciates CAISO’s proposals to move forward the identified issues in the near-term. Given the significant increase in battery storage operating in CAISO today, it is important to resolve these long-standing issues in a timely manner to facilitate efficient and transparent information in operations.

2. Please provide your organization’s comments on Outage Management Enhancements:

REV supports CAISO’s direction on OMS enhancements and the focus on the four components noted in the Straw Proposal. REV also supports these changes being addressed in the Outage Management BPM, though suggests the topic stay in this Initiative until stakeholders have fully vetted the proposed solutions before moving to a PRR.

On the outage reporting requirements, REV agrees with Vistra’s reporting threshold for changes exceeding 10 MW or 40 MWh, or 5% of values lasting 15 minutes or longer. On the recommendation to report within 60 minutes of discovery, REV suggests this should not be a strict timing requirement for reporting these issues. The vast majority of battery storage resources in CAISO are under control of Remote Operation Centers (ROCs); these ROCs operate several resources at one time and particularly in the night hours may not be able to report an issue within 60 minutes. However, if this is focused on reporting within time of discovery, rather than when the event occurred, it could be workable.

REV also requests that CAISO continue to pursue automatically accepting updates to outage cards, even if this is a longer-term implementation item.

3. Please provide your organization’s comments on Representation of Nonlinearity:

REV supports the near-term solution to represent nonlinearity in outage cards and longer-term to integrate power rates into the Master File.

REV does not agree with using the Plant Trouble nature of work (NOW) and does not agree that nonlinearity should be subject to RAAIM. REV supports Vistra’s suggestion to use “Technical Limitations not in Market Model” NOW instead, since a technical limitation is exactly what nonlinearity is. Nonlinearity does not mean that the energy is not available to CAISO, it is just that it is available at a rate different than the Pmax or Pmin. As noted in the stakeholder meeting, this is similar to gas generators that may take time to ramp up to reach their max dispatch, but they are not penalized for RA because of this technical limitation. Storage resources should not be effectively required to overbuild their project, which would add cost to RA resources in a time when energy affordability is a concern in the state. This could be an unaccounted for penalty to existing battery storage resources, which could lead to disruptions in the RA market. Further, foldback will always exist no matter the capacity of a resource, since it is inherent in Li-ion technology. If LSEs want to account for foldback in future RA contracts that could be a factor to consider in their evaluation of offers.

REV agrees with CAISO’s longer-term solution to include resource-specific values in the Master File and urges CAISO to implement this as soon as possible as it will be more durable and transparent.

REV is not opposed to exploring a biddable SOC participation pathway in the future, but does not suggests this is a lower priority item.

4. Please provide your organization’s comments on SOC Clarification:

REV defers comments on SOC clarification at this time.

5. Please provide any additional comments:

REV does not have any further comments at this time.

1. Please provide a summary of your organization’s comments on the Issue Paper & Straw Proposal on Outage Management, Nonlinearity, & SOC Clarification and May 9, 2025 meeting discussion:

San Diego Gas and Electric (SDG&E) is supportive of the proposed enhancements outlined in the Issue Paper & Straw Proposal on Outage Management, Nonlinearity, and SOC Clarification. SDG&E believes it is appropriate to prioritize near-term IT solutions for urgent operational challenges and then commence discussions on more complex policy topics such as bid cost recovery redesign and default energy bids. Given CAISO’s intention to start working on these enhancements quickly, with some changes to the BPMs to be operationalized as soon as Summer 2025, we offer the following comments for consideration.

2. Please provide your organization’s comments on Outage Management Enhancements:

The proposal for OMS enhancements included in the Issue Paper & Straw Proposal makes practical and meaningful improvements for owners and scheduling coordinators of storage resources. As discussed during the May 9 stakeholder meeting, the current tools in the outage management system (OMS) do not sufficiently account for the unique characteristics of storage resources. While each of the four improvements outlined by CAISO are important, SDG&E agrees that the most material improvement to OMS would be from making changes to support overlapping outage cards that can adjust availability, load max, max energy, and min energy on one card. Therefore, if there is to be any sequencing of the enhancements, SDG&E recommends this item be priority #1.

SDG&E also supports the addition of cause descriptions in the nature of work (NOW) to include storage-specific outage types as justification for certain NOW categories. Adding these clarifications is a positive enhancement that will better align the categories with the characteristics of storage resources, increasing the efficiency and consistency of outage requests. In addition, SDG&E supports the inclusion of rack outages in the “Plant Trouble” NOW category. However, it would be helpful to better understand CAISO’s concerns regarding the inclusion of rack outages in the “Plant Trouble” category and how that would prevent further discussion of best practices for state of charge (SOC) estimations or clarification of SOC expectations relating to voltage imbalance.

3. Please provide your organization’s comments on Representation of Nonlinearity:

In the short-term, SDG&E recommends using the “Technical Limitations Not in Market Model” NOW to represent nonlinearity (foldback) in the market. Currently, there is no way for a storage resource to operate in such a way that avoids infeasible dispatches at the upper and lower ends of its SOC, since the market model does not consider varying ramp rates and dispatches in those ranges are infeasible with the resource’s design capabilities. As it is not possible to incorporate nonlinearities of storage operation into the market model in the near-term, use of the “Technical Limitations Not in Market Model” NOW option to represent foldback and exempt the resource from RAAIM penalties is the most reasonable interim solution. This method will provide more transparency into the magnitude of foldback, allow greater visibility for operators, and improve the management of storage resources.

SDG&E also believes that it is critical to quickly move into discussions for a longer-term solution to nonlinearity. While SDG&E strongly prefers representing nonlinearity via resource-specific rates within the Master File, extending the use of the dynamic limit tool or developing a biddable SOC approach could both be workable methods for managing this existing technological limitation and should not be excluded from consideration.

4. Please provide your organization’s comments on SOC Clarification:

SDG&E requests more clarification on the downstream market operation impacts from changes to the definition of “available” energy in the BPM.

5. Please provide any additional comments:

No comment.

1. Please provide a summary of your organization’s comments on the Issue Paper & Straw Proposal on Outage Management, Nonlinearity, & SOC Clarification and May 9, 2025 meeting discussion:

The Six Cities do not oppose the CAISO’s proposed approaches to addressing these issues, and they specifically support the CAISO’s proposal not to provide an exemption from the Resource Adequacy (“RA”) Availability Incentive Mechanism (“RAAIM”) for storage resources experiencing nonlinearity/foldback issues. 

2. Please provide your organization’s comments on Outage Management Enhancements:

The Six Cities do not oppose the approaches outlined by the CAISO and look forward to continued discussion regarding potential adjustments to CAISO Business Practice Manual (“BPM”) provisions and outage management system (“OMS”) modifications to address the identified concerns.  As the storage fleet grows within the CAISO and Western Energy Market (“WEM”) footprint, it is critical to ensure that existing systems and procedures, such as outage reporting, are adapted to reflect the unique characteristics of the storage fleet.

3. Please provide your organization’s comments on Representation of Nonlinearity:

As a general matter, the Six Cities do not oppose the CAISO’s proposal regarding the representation of nonlinearity/foldback, including the proposal that, in the near term, unavailability due to nonlinearity/foldback should be reflected on outage cards with a “Plant Trouble” nature of work (“NOW”) and be accompanied by a corresponding comment clarifying that the resource’s outage is due to nonlinearity.  The Six Cities share the CAISO’s concern regarding the implications—namely, the exemption from RAAIM—that would be associated with use of the “Technical Limitations Not in Market Model” NOW.  There does not appear to be a justification to authorize a RAAIM exemption for outages due to nonlinearity, at least not within the timeframe by which a near term clarification for how market participants should report unavailability due to nonlinearity is sought.  Given the complexity of this issue and its relationship with policy issues regarding resource availability and the UCAP mechanism that are under consideration in the CAISO’s RA Modeling and Program Design initiative, the Six Cities concur in the CAISO’s overall approach of a simple, near term fix through the use of outage cards and continued work on a longer term solution.  

4. Please provide your organization’s comments on SOC Clarification:

The Six Cities understand the CAISO’s proposal to be continued discussion of this topic, with a goal of revising the CAISO’s Direct Telemetry BPM to specify how SOC is conveyed to the CAISO through telemetry.  At this time, the Six Cities do not oppose this proposal. 

5. Please provide any additional comments:

The Six Cities have no further comments at this time.

1. Please provide a summary of your organization’s comments on the Issue Paper & Straw Proposal on Outage Management, Nonlinearity, & SOC Clarification and May 9, 2025 meeting discussion:

Southern California Edison (SCE) appreciates the opportunity to comment on the Storage Design and Modeling Issue Paper and Straw Proposal on Outage Management, Nonlinearity, and State of Charge Clarification.

SCE’s comments can be viewed under the subsequent questions.

2. Please provide your organization’s comments on Outage Management Enhancements:

CAISO Should Provide Clarity for Outage Reporting by Updating the Tariff 

Southern California Edison (SCE) aligns with Vistra in recognizing the urgent need to address the limitations within the current CAISO tariff for outage reporting. The existing tariff, primarily designed for traditional generators, fails to adequately accommodate the unique operational characteristics of battery storage resources. Specifically, it lacks detailed requirements for outage reporting related to state of charge (SOC) and charging capabilities. This gap can lead to inconsistent reporting and management, potentially impacting market operations and reliability. 

Incorporating Outage Reporting Guidelines into the CAISO Tariff 

In the Issue Paper and Straw Proposal, CAISO appears open to making changes to the Outage Management BPM. While SCE supports changes to the BPM to provide guidelines for temporary solutions, SCE strongly advocates that CAISO incorporate outage reporting guidelines into the CAISO tariff. Tariff amendments provide a legally binding framework, ensuring consistent compliance and preventing inconsistencies. This approach offers a stable, long-term solution that can be enforced and enhances market transparency. 

SCE Supports CAISO’s Temporary Outage Enhancements Proposal 

SCE appreciates CAISO's openness to enhancing the current OMS system. The Straw Proposal mentions that CAISO will focus on the following improvements to OMS: 

• Allow for overlapping outage cards that can adjust Availability, Load Max, Max Energy, and Min Energy values. 

• Allow non-NULL values in addition to NULL for other cards. 

• Create a single Out-of-Service checkbox for Non-Generator Resources (NGRs). 

• Allow for Load Max (Pmin) rerates on Test Energy cards during New Resource Implementation. 

It is not clear in the proposal whether the focused improvements mentioned above would be a re-design of the OMS system to accommodate storage or modifications to the current design. SCE perceives it to be a quick fix solution utilizing the current OMS design, which may lack the flexibility for energy storage market participants to properly address the availability of the resource, including nonlinearity issues. SCE recommends CAISO work with stakeholders to obtain feedback for a new design that is efficient and can be used as a long-term solution. 

CAISO Should Implement an MF+OMS Redesign for Energy Storage Resources 

As mentioned in SCE’s previous comments, CAISO should consider a redesign of how energy storage resources are incorporated into the market. This redesign would include how storage resources are bid in the market, including how outages are reported. One idea for consideration would be to leverage designs similar to those used for multi-stage generation. A long-term solution that leverages defining SOC-based segment performance in the MF could consequently enable the same segments to be adjusted on outage cards. A new OMS outage design to support energy storage resources would include the ability to report outage information for specific ranges of SOC. This enhancement, in combination with CAISO's proposal to incorporating foldback characteristics into the Master File (MF), would be a major improvement to the current design.  

3. Please provide your organization’s comments on Representation of Nonlinearity:

SCE Supports the Use of “Plant Trouble” NOW 

SCE agrees with CAISO's interim proposed solution to use the “Plant Trouble” nature of work (NOW).   SCE sees this as an interim solution until an improved design to OMS is developed and implemented.      

SCE Supports Master File Enhancements to Represent Nonlinearity 

SCE continues to support CAISO’s proposal to use the Master File to model the capabilities of batteries at different state of charge levels in the long-term approach.  In SCE’s view, the Master File will establish a baseline working capacity for battery storage resources and will serve as a reference point for outage reporting and performance evaluations. SCE suggests CAISO implement a standardized process for verifying performance at these SOC-based segments for the purpose of establishing MF values. This would provide a strong logistical basis for retrofitting or re-negotiating existing battery assets under contract. Using the Master File in combination with a new OMS design for Energy Storage resources as mentioned under question #2 would provide the best results for resources to accurately represent the different nonlinearity issues.   

“Technical Limitation Not in Market Model” should not be used for Linearity Issues 

SCE also agrees with CAISO and the CPUC that resources should not use “Technical Limitation not in Market Model” NOW as a temporary measure to represent nonlinearity.  SCE sees the use of that NOW being abused due to Resource Adequacy Availability Incentive Mechanism (RAAIM) exemptions.  Furthermore, SCE believes that using this NOW would have negative consequences by masking and overstating what actual capacity is available to the market.

4. Please provide your organization’s comments on SOC Clarification:

SCE supports CAISO leveraging this initiative to explore and develop requirements to include in the Direct Telemetry BPM. SCE looks forward to participating in discussions regarding telemetry standards and recommends CAISO also explore testing standards that would enhance the accuracy of reported SOC.

5. Please provide any additional comments:

SCE does not have any additional comments.

1. Please provide a summary of your organization’s comments on the Issue Paper & Straw Proposal on Outage Management, Nonlinearity, & SOC Clarification and May 9, 2025 meeting discussion:

The Salt River Project Agriculture Improvement and Power District (SRP) appreciates the opportunity to provide feedback on the recent working group discussion regarding the Storage Design and Modeling initiative.  SRP supports allowing batteries to submit overlapping maximum values across outage cards and encourages a streamlined and automated process for submitting and updating battery outage cards to reduce the risk of inconsistencies. SRP supports using the Outage Management System (OMS) as a short-term fix to address non-linearities, but is concerned it may delay a more robust long-term solution. SRP requests that CAISO provide clarity on the implementation plan and management's estimated timeline for addressing non-linearity through the Master File. SRP also supports clearer SOC definitions in the Business Practice Manuals (BPMs) with the caveat that many BESS units in SRP territory are operated by third-party vendors via Power Purchase Agreements (PPAs), and as such, may have limited ability to choose the method of how SOC telemetry is provided.

2. Please provide your organization’s comments on Outage Management Enhancements:

SRP supports allowing batteries to have overlapping load maximum values across different outage cards. For improved operational clarity, it would be beneficial if the system automatically applied the most restrictive value during overlapping periods, then transitioned to the next applicable load maximum once the initial period concludes.

SRP has observed a workflow inconsistency when submitting battery outage cards via iTOA and linking them to CAISO. Specifically, iTOA allows us to mark the availability of the discharge component as an outage, it does not provide an option to mark the load maximum as unavailable. As a result, SRP must manually access webOMS to update the load max status separately.

To streamline this process and ensure operational accuracy, SRP recommends that when a battery outage is submitted and linked to CAISO, both the availability and load max values default to not available.  Since these two aspects of battery operation are inherently linked, there should not be a scenario where one is available while the other is not. SRP is unsure whether this is a limitation within iTOA or a configuration issue within CAISO, but aligning these systems would significantly improve efficiency and reduce the risk of oversight.

3. Please provide your organization’s comments on Representation of Nonlinearity:

SRP agrees that adjusting the Master File layout and ingestion process to include parameters describing the aspects of the non-linearities of the batteries is the correct way to address the problem, as it is essentially a matter of the innate operating characteristics of the battery itself. The purpose of the Master File is to capture such characteristics of the participating units.

While SRP will support using the OMS as an interim solution to address non-linearities in the near term, there is concern that having this solution in place will reduce the incentive to implement a more robust solution in a timely manner. SRP requests some clarification regarding the expected timelines to implement the necessary changes in the Master File process.

Similarly, developing a Biddable SOC approach is compelling, but seems like the most complex of all the proposed solutions.  SRP requests additional detail on what such SOC bids would look like and how long it would take to implement.

SRP agrees with the DMM that the use of the dynamic limit tool to manage non-linearities is less preferable than updating the Master File process. While it might serve as a short-term solution that could be stood up quickly and might be more flexible than using the OMS, SRP shares the DMM concerns about the lack of transparency associated with the dynamic limit tool.

4. Please provide your organization’s comments on SOC Clarification:

SRP agrees that increased clarity of the definition of SOC characteristics as defined in the BMPs would be useful and looks forward to participating in working groups dedicated to this process. One related issue is that many BESS units in SRP's control area are in fact operated by third-party vendors via PPAs and as such, SRP may have limited flexibility in determining the exact method by which SOC telemetry is provided.

5. Please provide any additional comments:

N/A

1. Please provide a summary of your organization’s comments on the Issue Paper & Straw Proposal on Outage Management, Nonlinearity, & SOC Clarification and May 9, 2025 meeting discussion:

Terra-Gen, LLC (Terra-Gen) appreciates the opportunity to comment on the CAISO’s May 9, 2025, Storage Design and Modeling meeting and Issue Paper. Terra-Gen supports CAISO's efforts to improve outage management, address market nonlinearity, and clarify State of Charge (SOC) accounting. Terra-Gen supports changes that can be put in place quickly and we urge CAISO to continue to pursue these proposed changes, especially the interim solutions that will bridge gaps until long-term improvements are ready.

Terra-Gen’s feedback at this stage of the effort includes the following main takeaways:

• Support CAISO's proposed Outage Management System (OMS) changes and encourage adding automatic outage card updates in phases. Any changes to the Business Practice Manuals (BPMs) should be thoroughly discussed in the policy process before becoming official Protocol Requirement Revisions (PRRs).
• Support using the dynamic limit tool for storage as a short term/interim solution for reflecting nonlinearity “foldback” impacts. This approach could be a workable temporary fix that would be better than the use of outage cards that would take longer to flow through CAISO’s processes.  The dynamic limit option should be used while a more robust solution for the market modeling improvements and use of Master File parameters and telemetry to reflect nonlinearity is developed.
• Disagree with CAISO’s assertion that Resource Adequacy Availability Incentive Mechanism (RAAIM) is appropriate for “foldback” nonlinearity impacts and support an exemption for nonlinearity. This issue would primarily impact resources that are already built and contracted, and "foldback" is a physical limitation not currently reflected in the market model.
• Terra-Gen supports CAISO’s efforts to explore SOC management updates, including expanding the Direct Telemetry BPM to ensure that reported instantaneous SOC and maximum continuous energy limits accurately reflect what's available to the market, and advocates for policy-level discussions on these changes before CAISO submits a PRR.

2. Please provide your organization’s comments on Outage Management Enhancements:

Terra-Gen supports the proposed OMS enhancements generally, as these specific improvements will help make resource availability and operations more accurate and efficient. We specifically support the following updates:

• Overlapping outage cards that can adjust Availability, Load Max, Max Energy, and Min Energy on a single card. This simplifies things and improves accuracy.
• Allowing non-NULL values for other cards related to ancillary services, providing more detailed information.
• A single "Out-of-Service" checkbox for Non-Generator Resources (NGRs), which streamlines outage management for these resources.
• Allowing Load Max (Pmin) rerates on Test Energy cards during New Resource Implementation, which is crucial for accurately reflecting capabilities during testing.

Terra-Gen understands that implementing automatic acceptance of forced outage card updates might need to be delayed due to other priorities. However, we ask CAISO to provide an estimated timeline for this enhancement. Automatic updates are crucial for real-time market accuracy, reducing errors, and improving overall operational efficiency. If this feature is delayed indefinitely, it may never happen, which would be a missed opportunity for significant market improvement.

Furthermore, Terra-Gen believes that any BPM changes should first be fully vetted through the stakeholder policy process before they become PRRs. This approach allows for a more collaborative discussion and helps build consensus, leading to a smoother PRR process later. Terra-Gen also urges CAISO to ensure that these improvements are tested and vetted through market simulation to ensure the functionality is working as intended without adverse consequences, including how the resulting changes will flow through related CAISO systems such as the Customer Interface for Resource Adequacy (CIRA) and Settlements to ensure accurate outcomes for issues such as substitution outcomes and related incentive mechanism settlement impacts. 

3. Please provide your organization’s comments on Representation of Nonlinearity:

Terra-Gen supports CAISO's efforts to develop a staged approach to addressing foldback: a quick, near-term solution while also developing a more comprehensive, long-term fix for the market model or Master File data.

Near term, Terra-Gen supports the dynamic limit tool option as an interim solution and believes the use of outage cards is essentially an infeasible solution in most circumstances, with limited benefit due to the timeframe associated with this option. It appears that the use of outage cards will take too long to implement these foldback impacts into the CAISO’s market processes within the timeframes they become impactful. Thus, Terra-Gen recommends the dynamic limit tool option would be more effective to provide faster implementation of foldback impacts as compared to the use of outage cards which would certainly take longer to flow through OMS and into market processes. We recommend that CAISO should review the timelines under each option to compare the potential difference in lag impacting how quickly these foldback impacts could be implemented in market processes. Of key importance, Terra-Gen believes any near-term solution should only be a temporary step until better modeling is in place.

During the May 9, 2025, stakeholder meeting the CAISO Department of Market Monitoring (DMM) expressed concern about the use of dynamic limits for reflecting foldback impacts as something that would need to be monitored for gaming or manipulation, thus it would not be a preferable interim solution in their view. Related to this input, CAISO staff also requested input on how CAISO’s DMM could monitor the use of dynamic limits. Terra-Gen responds to this discussion with the following feedback: The use of outage cards is also something that is monitored for appropriateness and manipulation as well, and we believe that the use of dynamic limits generally by hybrid limits has been done conservatively and without concerns over manipulation in the past, thus there should not be a large concern about such practices to be used by standalone storage if allowed to use dynamic limits for this foldback purpose. Additionally, Terra-Gen notes that the CAISO has access to the SOC telemetry and similarly has maximum power capability, i.e., “Discharge Power Available” telemetry point, each of which could be used together to audit and monitor the use of dynamic limits for foldback by standalone storage resources.

Should CAISO take the ill-advised route of proposing to require the use of outage cards to reflect foldback impacts, Terra-Gen provides the following feedback in advance to help avoid additional unfair and discriminatory treatment for storage assets.  Terra-Gen recommends that, if CAISO does require outage cards, storage resources should be allowed to use the Technical Limitation not in Market Model” Nature of Work (NOW) card.  CAISO and some other stakeholders have also expressed concerns about using a "Technical Limitation not in Market Model” NOW which includes RAAIM exemptions, for issues like foldback, preferring outage cards without such exemptions. CAISO has stated it believes exemptions could reduce incentives for resources to overbuild or procure enough capacity. While Terra-Gen understands the importance of incentives, we strongly disagree that a temporary RAAIM exemption would be appropriate or would significantly undermine incentives, especially since this is an interim measure. In fact, it is not fair or appropriate to apply RAAIM to these outages, and Terra-Gen provides the following support for our position on this issue:

• Existing Resources: Most affected resources are already operating or well into their development, so they can't easily respond to RAAIM exposure by adding more capacity in the short term.
• Contract Limitations: These resources are typically under contract, limiting opportunities to change procurement based on short-term penalties.
• Physical Limits: "Physical foldback" is an inherent technical limitation, not something that can be fully fixed by just scaling capacity. It will always exist regardless of resource size.
• Cost vs. Penalty: Given the large investments in energy storage, RAAIM penalties for a temporary issue might not be enough to incentivize overbuilding. It might even be cheaper for participants to just accept the penalty than to incur the much higher costs of adding extra, potentially underutilized, capacity. This would lead to higher costs for the market and ratepayers, which could be avoided with a RAAIM exemption.

For these reasons, Terra-Gen believes the "Technical Limitation not in Market Model" NOW is appropriate. Crucially, any unavailability under this NOW should not count against a resource's availability performance and should not be subject to RAAIM charges.

Accurate modeling of nonlinearity would allow the market to dispatch resources consistent with their true operational characteristics. The market already recognizes similar dispatch limits for thermal resources (like ramp limits) without applying RAAIM, and energy storage should be treated similarly.  Therefore, Terra-Gen opposes CAISO’s proposed preference to use the “Plant Trouble” NOW card, as this is not the most appropriate outage type, which is plainly obvious since the foldback issue is a characteristic inherent to the resource design – not plant maintenance, communication issues, safety management, control system or electrical issues, or other failure type.

Ultimately, CAISO should improve its market modeling to reflect nonlinearity issues such as foldback and not these stop-gap measures.  Terra-Gen recommends that CAISO work on a durable solution that will properly reflect these operational limitations, including the following aspects: CAISO should utilize the resource characteristics that can be provided to state the expected foldback design parameters; and employ the “Discharge Power Available” and SOC telemetry points in its market processes as appropriate award and dispatch constraints.

4. Please provide your organization’s comments on SOC Clarification:

Terra-Gen supports CAISO’s consideration of potentially expanding the Direct Telemetry BPM to clarify that the instantaneous SOC and the maximum continuous energy limit should represent the amounts that are available to the market at the time these values are conveyed through telemetry. We suggest further discussions on potential changes to the Direct Telemetry BPM within this policy process before CAISO proceeds with submitting a PRR.

5. Please provide any additional comments:

1. Please provide a summary of your organization’s comments on the Issue Paper & Straw Proposal on Outage Management, Nonlinearity, & SOC Clarification and May 9, 2025 meeting discussion:

Vistra strongly supports CAISO's prioritization of practical improvements to outage management, foldback challenges (i.e., nonlinearity), SOC telemetry clarifications, and modeling changes to ensure Flexible Ramping Product (FRP) awards are feasible.

2. Please provide your organization’s comments on Outage Management Enhancements:

Vistra appreciates CAISO's recognition of the urgent need to evolve the Outage Management System (OMS) functionality and the Business Practice Manual (BPM) rules to better support storage outage reporting to be able to timelier reflect availability in market operations and ensure reporting consistency. We support CAISO's commitment to pursue OMS improvements.

Vistra would like to request the CAISO re-evaluate its initial decision on automatic acceptance of updates to forced outage cards. An important clarification to our proposed improvement is that we intended it to be implemented for all resources as this is a general challenge with OMS – not storage specific. This can be seen in Bonneville Power Administration’s 2024 Policy Roadmap scope item it requested for the same problem statement and solution.[1] This market-wide solution will help all Scheduling Coordinators across the Western Energy Imbalance Market to better manage outages in real-time and speed up the time for updates or cancellations to be incorporated into the markets. With this understanding that it would be a general change to auto accept, we request the CAISO reconsider its feasibility.

We strongly support CAISO's agreement to revise Section 4.1 of the Outage Management Business Practice Manual (BPM) to clarify outage reporting thresholds and to incorporate SOC-related thresholds like those used for maximum capacity reporting. Vistra also appreciates CAISO's openness to including additional Nature of Work (NOW) descriptions for storage-specific failure modes in Section 3.4 of the BPM. At this time, Vistra does not understand why physical outages due to voltage imbalances would be on a different nature of work because the rack/cell outages due to imbalances occur when the unit needs to be taken offline to perform the rebalancing.[2] We request the CAISO propose Business Practice Manual (BPM) redlines for consideration in the draft final proposal.

[1] Bonneville Power Administration, 2024 Policy Roadmap Submissions, May 8, 2024, Slide 37, https://stakeholdercenter.caiso.com/InitiativeDocuments/Presentation-Annual-Policy-Roadmap-Catalog-working-group-May8-2024.pdf.

[2] Section 9.3.10.3.1 of the Tariff requires forced outage reporting within 60 minutes of identifying an issue for changes that last fifteen minutes or longer. Vistra believes in most instances imbalances would not be reflected in outages while a resource is offering to bring a rack or group of cells back into balance because it would need to be self-scheduling to reflect the price insensitive need to operate to bring it back into balance. If the self-schedule is insufficient in allowing for this rebalancing then an outage would be needed under plant trouble to be able to operate outside market to rebalance the cells or racks.

3. Please provide your organization’s comments on Representation of Nonlinearity:

Vistra appreciates the CAISO acknowledging there is a market modeling limitation whereby it is not currently able to model the impact to maximum capacity (Pmax) or minimum capacity (Pmin) as function of state of charge levels (i.e., foldback, nonlinearity). We support a robust solution modeling discharge and charge current rates. While Vistra supports exploring a biddable SOC paradigm, we do not believe it will obviate the need for modeling the current rates as long as Pmax and Pmin continue to be modeled. Further, we want to ensure that biddable SOC is not synonymous with the old Energy Storage Resource participation model idea. A SOC reserve requirement, either price-based constraint or biddable, should be feasible to implement in the existing Non-Generator Resource model if there is value in adding this functionality.

For the near-term solution, using outage cards to reflect foldback impacts is feasible as long as the nature of work can be changed to a more accurate cause. Continuing to use the Plant Trouble NOW is not appropriate for this type of outage. The true definition of this outage is a technical limitation to the resource that is not currently modeled in the market. We are waiting for CAISO to enhance its model to model this limitation and have been waiting for five years.

CAISO raised concerns that it has received about making the Technical Limitations not Modeled card available because it is exempt from The Resource Adequacy Availability Incentive Mechanism (RAAIM). The two theories put forward for minimizing foldback were: (1) overbuilding storage beyond 4 hours or (2) selling less Net Qualifying Capacity (NQC). We address both inaccurate theories below. These concerns are misplaced

First, foldback is not a characteristic that overbuilding can address nor does contracting less of the asset in a MW amount address this concern in a reasonable way given how limited in time foldback impacts last. Second, reducing the contracted quantity cannot minimize foldback either. We provide the following example and explanation.

For example, consider a storage resource that is a flex category 1 storage resource with Pmin from -100 MW and Pmax of 100 MW with an overbuild has 500 MWh allowing it to discharge for up to five hours. This storage resource has a Net Qualifying Capacity of 100 MW that has a four-hour minimum duration requirement subject to RAAIM for five hours and Effective Flexible Capacity of 200 MW with a two cycle for a three-hour minimum duration requirement across the 17-hour period from 5:00 a.m. through 10:00 p.m.

This storage resource overbuilt to add an hour beyond its generic RA four-hour requirement and two hours beyond its flexible RA three-hour two-cycle requirement. Assume the resource has physical limitation on its current rates when it operates at Pmax when the SOC drops below 90% of its depth of discharge in the bottom 10% of its SOC range. Similarly, it would experience increase of its Pmin as the SOC reaches above 90% of its SOC range. The bottom 50 MWh and top 50 MWh of SOC will take longer to provide because the Pmax is reduced and the PMin is increased given change in resistance impacting the respective current rates. The MWh are available but the dispatch is limited temporarily to a slower discharge or current rate.

For this storage asset to “overbuild” so that foldback never occurs in its 17 hour RAAIM assessment period, it would have to have continuous operate capability beyond 17 hours. This is inconsistent with the definition of the flexible category 1, base ramping, product. Flex Cat 1 requires a resource to be available for two cycles across three minimum duration requirement to support its base ramping flexible capacity requirements. If providing two full cycles, one could see foldback impacts when it (1) nears the bottom of its range after the morning net peak hours, (2) nears the top of its range as it charges back up for the evening net peak hours, and (2) as it nears the bottom again as it discharge during the net peak hours. The presumption that a storage resource should be built to be able to operate continuously more than 17-hours, well-beyond a long-duration energy storage resource at eight hours, is inconsistent with Integrated Resource Planning, CPUC RA rules, and CAISO Tariff Section 40.

The only way for “overbuilding” to achieve the theory discussed is not actually overbuilding alone but also withholding from the CAISO grid operations the full MWh of the asset. If this hypothetical storage resource would have built 500 MWh but then registered in Master File a minimum continuous energy limit of 50 MWh and a maximum continuous energy limit of 450 MWh this would violate the CAISO’s Tariff.[1] Further, it would needlessly remove 100 MWh from the storage’s capability that we should want to be available at the discharge or current rates especially on a stressed day.

CAISO’s RAAIM methodology is assessing its availability for longer than its contractual obligations because it has a 24 hour must-offer obligation and is assessed across five hours for generic RA and 17 hours for flexible RA. Selling less capacity is not the issue at hand. This storage asset in this example did not sell any capacity associated with foldback impacts which this scenario assumes triggers between 0-50 MWh and 450 MWh and 500 MWh equally 100 MWh that were not sold but in the overbuild.

The operator has sold less than its state of charge range selling 400 MWh across four continuous hours up to its 100 MW Pmax. The asset also sold 200 MW EFC for two cycles across three continuous hours. It can meet both of these RA contract obligations. For generic RA requirements, the storage resource meets its four-hour minimum duration requirement at its contracted NQC available. It is also fully available from a MWh perspective through the entire Availability Assessment Hours (AAH). For flex RA requirements, the storage provides two more consecutive hours than the three-hour minimum.

[1] CAISO Tariff Section 4.6.4 Identification of Generating Units states Master File values must be “accurate reflection of the design capabilities of the resources” to exclude storage’s state of charge registered values from this requirement and allow market-based parameters to be filed in lieu. Vistra does not support this approach.

4. Please provide your organization’s comments on SOC Clarification:

Vistra appreciates CAISO's efforts to clarify how SOC should be calculated and conveyed through telemetry. We support enhancing Section 14.5 of the Direct Telemetry BPM to require that SOC and energy limit values reflect energy actually available to the CAISO at the time of submission. Our concern surrounds the need to make sure telemetered values are accurate reflections of availability to receive a dispatch instruction regardless of whether it is issued by the market or an exceptional dispatch automatic or verbal. The telemetered values should align with the resource’s registered values as adjusted by outage cards. The market-available values may be adjusted further reflecting market-based parameters through the Lower State of Charge Limit and Upper State of Charge Limits. CAISO should refine the existing definition to remove this ambiguity and market clear it is what is available to CAISO operations.

In the stakeholder meeting, CAISO raised under this discussion outages to reflect foldback (“non-linearity”) and depth of discharge (“significant opportunity costs for full discharge”). First, non-linearity does not lead to energy not being accessed at low State of Charge but instead changes the power output in MW available due to discharge current rate impacts where the SOC is available the rate of its dispatch is slowed. Second, Depth of Discharge (DoD) does introduce opportunity costs for discharging into the lower portions of the SOC and is highly dependent on the resource’s negotiated warranty. It is worth noting that there may be some warranties that would void if you violate the DoD limit even once, which should be treated as a physical limit where the Minimum Continuous Energy Limit should be equal to the limit in the warranty. For other warranties, these limits may be more flexible where the resource has to stay above a DoD average across a period of time that will allow its opportunity costs to be reflected to manage that asset.

Our experience is that CAISO has two approaches to accommodate when a storage resource has a DoD limit that it needs to reflect in the market. The first is through the registration of the Variable Operations & Maintenance (VOM) adders. Storage resources have to negotiate the storage VOM included in the storage Default Energy Bid calculation and the VOM should be a function of DoD and cycle limitations since you can provide these limits in the negotiation and they can inform your negotiated VOM. While we continue to see challenges with other parts of the Default Energy Bid methodology, our experience is the negotiated VOM process has been able to respect these limitations in establishing the VOM. In the instance that storage may be nearing the DoD limitations in the warranty, storage can use the Lower State of Charge Limit to increase its market-based SOC so that it can preserve that SOC until it is able to allow economics to influence the access to that area. When using the bid parameter, if there is an emergency CAISO could still access its lower SOC range through Exceptional Dispatches. Given this experience, we are struggling to understand the problem statement being raised and seek clarification.

5. Please provide any additional comments:

Vistra understands the CAISO is committed to an urgent market software change to address the concern that certain Flexible Ramping Up (FRU) awards may be infeasible if there is insufficient SOC to meet all of the resource’s awards. We still have questions about exactly how the proposal will be implemented.

Vistra raised the need to consider including Flexible Ramping Product in the SOC calculation in our questions on the Energy Storage Enhancements proposals. In our comments to the revised straw proposal, Vistra asked the CAISO to address questions on why CAISO was not including Flexible Ramping Product awards in the proposed State of Charge calculation changes.[1] The CAISO never responded to our questions in that effort. We are grateful that this discussion is being revisited here at least for Flexible Ramping Product up.

Vistra requests a single clarification be made to the BPM redlines. The formulas refer to FRUi,t  where t is the time interval index. We request that CAISO clarify whether t is the binding interval for FRU award (i.e., the advisory interval result) or binding interval for energy award (i.e., the binding interval result). We believe this would be implemented where t for FRU is the binding FRU result in the next interval not the same interval, but we find it unclear at this time. Please update the formula description to make clear whether the awards are in the same interval or in the intervals associated with the products award. Please see below a figure from the technical appendix for FRP to illustrate our question clearly:[2]

As to excluding the Flexible Ramping Down product, Vistra supports the CAISO excluding FRD in the temporary solution largely because historically CAISO has sufficient downward flexibility across the year. While downward flexibility could change over time, at this time there would not be a reliability issue of excluding.

[1] Vistra Comments on CAISO Energy Storage Enhancements Second Revised Straw Proposal, August 5, 2022, https://stakeholdercenter.caiso.com/Comments/AllComments/6211a605-5db0-45c7-a959-3b1df57bb7ba#org-5bebc51b-7df5-4710-85c5-9b8bfbd270ad.

[2] See Flexible Ramping Product, Technical Appendix, Figure 1, https://www.caiso.com/documents/drafttechnicalappendix_flexiblerampingproduct.pdf.

1. Please provide a summary of your organization’s comments on the Issue Paper & Straw Proposal on Outage Management, Nonlinearity, & SOC Clarification and May 9, 2025 meeting discussion:

WPTF supports CAISO’s efforts to enhance outage management, address nonlinearity in the market, and clarify SOC accounting. We urge CAISO to maintain momentum on proposed changes, particularly where interim solutions are needed to bridge gaps before long-term improvements can be implemented. Our comments emphasize the importance of inclusive stakeholder engagement, cost-effective short-term measures, and improved transparency around market mechanisms and modeling assumptions.

Our comments below reflect the following:

• Support CAISO’s proposed OMS changes and encourage inclusion of automatic outage card updates with a phased approach for all resources;[1] BPM changes should be vetted through the policy process before PRRs.
• Support near-term use of outage cards or dynamic limit tool to address nonlinearity while we develop a more robust change to the market model and/or Masterfile.
• Disagree with CAISO’s concern that RAAIM exemption for nonlinearity reduce incentives, especially given this is a short-term solution; impacted resources are already developed and contracted for, and foldback is a physical constraint that is not currently in the market model.
• Appreciate CAISO acknowledging that the current proposed change to SOC AT to reflect FRU overstates the impact and urge CAISO to consider a more robust solution that allows for balanced treatment of FRU and FRD
• Request refresher on DAME envelope equations, evaluation of how well the ASSOC constraint is currently constraining FRU awards due to insufficient SOC, and clarification on real-time SOC updates based on telemetry.

[1] The challenges with manual approvals of changes to forced outages was raised in the 2024 Policy Catalogue process by both storage operators and non-storage operators. WPTF supports a solution that addresses the concerns raised by both Bonneville Power Administration and storage operators clarifying that this issue impacts all resources equally. See slide 37 for Bonneville’s policy issue presented on May 8, 2024, https://stakeholdercenter.caiso.com/InitiativeDocuments/Presentation-Annual-Policy-Roadmap-Catalog-working-group-May8-2024.pdf.

2. Please provide your organization’s comments on Outage Management Enhancements:

WPTF supports CAISO’s proposal to implement the change to OMS as outlined on Slide 16 of the presentation. We also urge CAISO to reconsider implementing automatic acceptance of updates to forced outage cards for all resources. While CAISO cited the significant implementation effort as the reason for not pursuing this change at this time, it appears the complexity is because CAISO was evaluating allowing automatic approvals only for storage resources based on the stakeholder call discussion. However, the challenges with manual approvals of forced outages has been raised by non-storage operators such as Bonneville Power Administration. WPTF requests the CAISO reevaluate the feasibility of allowing automatic approvals of updates to forced outages for all resources before finalizing its proposal. If CAISO confirms that the automatic approval improvement cannot be implemented in this track, we request that the proposal remain within the policy framework, with consideration for a phased implementation approach for all resources. Deferring such enhancements indefinitely often results in them never being revisited.

Additionally, we request that any changes proposed through the BPM process be first developed and thoroughly vetted through this stakeholder policy initiative before advancing to PRRs. Doing so will create a smoother PRR process by allowing stakeholders and CAISO to build consensus on proposed changes prior to reviewing draft BPM language. Moreover, the policy stakeholder process enables a more robust and collaborative dialogue than what is typically possible through the PRR process.

3. Please provide your organization’s comments on Representation of Nonlinearity:

WPTF supports the dual-path approach of developing a near-term solution while concurrently working toward a more comprehensive model and/or Masterfile data change to address nonlinearity.

For the near-term, WPTF supports continued evaluation of both outage cards and the dynamic limit tool. We recommend a comparative analysis that outlines the pros and cons of each approach, with the understanding that this solution is interim while more robust modeling updates are pursued.

During the stakeholder meeting, CAISO raised concerns about using a NOW that includes RAAIM exemptions due to foldback, preferring the use of outage cards without such exemptions. CAISO's concern appears to stem from what may be an inaccurate belief that exemptions could reduce incentives to minimize foldback. CAISO indicated that it thought potentially a market participant could minimize foldback occurring if they overbuild resources or procure less capacity from the resource. While we understand the importance of market incentives, we respectfully disagree that a temporary RAAIM exemption would meaningfully undermine those incentives, especially given this is an interim measure.

First, most of the affected resources are either already operational or far enough along in the interconnection process that there is little to no ability to respond to RAAIM exposure through additional capacity development in the near term. Second, these resources are likely already contracted, limiting opportunities to modify procurement in response to short-term penalties. Third, even if resources could add capacity, physical foldback is a technical limitation that cannot be fully addressed by scaling capacity alone. It will always exist regardless of the size of the resource. Lastly, adding additional capability to a resource and/or contracting for more capacity for a short-term issue introduces long-term costs that are ultimately borne by the market and ratepayers, costs that could be avoided through a temporary RAAIM exemption. For a penalty to be appropriate as means to address incentive concerns, participants would have a need and capability to react. Given the magnitude of investment and contracting costs relative to RAAIM penalties, it could be the case participants do not respond and overbuild or contract for more capacity because it is more costly to do that than accept the RAAIM penalty.

For all the reasons noted above, we believe the “Technical Limitation not in Market Model” NOW remains an appropriate NOW. In fact, the very nature of these technical limitations that are not yet reflected in the market model justifies the use of such an outage card as an interim solution. 

4. Please provide your organization’s comments on SOC Clarification:

WPTF supports further discussions on potential changes to the Direct Telemetry BPM within this policy process before the CAISO proceeds with submitting a PRR. Additionally, we believe it may be worthwhile exploring to what extent the high opportunity costs related to depth of discharge or voltage imbalances should/could be reflected in the market as another way to address the inaccessible energy concerns.

WPTF has submitted feedback through both the PRR process and the May 13th comment window on the proposed changes to the SOC AT formulation, which aims to reflect the expected impact of FRU on SOC. In those comments, we noted CAISO’s acknowledgment that:

1. The current formulation is overly conservative, assuming 100% FRU deployment in the awarded interval.
2. The actual ramping and SOC impacts occur over two intervals, not solely within the award interval.
3. FRD is not yet incorporated.

We appreciate CAISO’s recognition of these limitations and its commitment to developing a more robust long-term solution.

WPTF agrees with the principle that FRU and FRD should be treated symmetrically. However, as discussed during stakeholder meetings, simply extending the current approach to include FRD could distort market outcomes, e.g., the optimization may over-award FRU/FRD to support regulation awards, similar to past behavior seen in testing. We therefore encourage CAISO to consider an alternative approach.

CAISO has indicated interest in expanding the DAME envelope equations to include FRU and FRD. We request a refresher on these equations, along with concrete examples, so stakeholders can better understand their mechanics. We are concerned that these equations may already be too restrictive and may not be suitable for layering in additional products without further refinement. It would also be beneficial to revisit the ASSOC constraints currently in use, as these already limit FRP awards based on SOC.

Moreover, it’s essential for CAISO and stakeholders to clearly understand how FRU is procured and when it is actually deployed. The current formulation assumes immediate and full deployment, which does not align with operational realities. A resource awarded FRU may not see any SOC impact if not dispatched for ramping. Even when used, the impact typically begins halfway through an interval and ends in the next, which may or may not include the awarded interval.

Lastly, in the real-time market, SOC is updated via telemetry. We recommend CAISO provide stakeholders with a walkthrough of how, when, and which SOC values are updated in real time for market operations and for grid operations. In theory, if a resource is used for FRU, its lower SOC would be fed back into the market, creating a feedback loop that should naturally moderate SOC assumptions in future awards.

5. Please provide any additional comments: