CAISO Response to PG&E comments ()

PG&E raised a number of question in its comments to the Energy Storage PRR versus proposing specific edits to the proposed PRR. CAISO will attempt to answer those questions here by section.

PG&E Comment 1, Question 1: “Wouldn’t most changes to a fuel source result in a rejection because any change in fuel source, whether wind, solar PV, or energy storage, because they would have an inherently different electrical control scheme and transient response?”

No, the CAISO and Participating TOs have allowed projects to change fuel types, as discussed in this section of the BPM so long as the change in electrical characteristics is not substantial. The exceedance factor for the old fuel-type is used to determine the allowed MW capacity once the project is changed to the new fuel type. In the past, for example, the CAISO and Participating TOs have allowed projects to change from wind to solar and vice versa.

If no restudy is required, how do we address the electrical control scheme and transient response difference from the different fuel sources? As written, due to the electrical characteristic changes, any fuel source change or adding energy storage would require a restudy and therefore would be rejected.

PG&E Comment 1, Question 2: Not all energy storage will be inverter-based either. How will these revisions address compressed air or other types of energy storage technology?

The CAISO agrees that the BPM may need to evolve with technology (as the CAISO is doing here); however, the only present change in this section is to add “MW” eight lines down from the top of the first paragraph. This section has existed since the inception of the BPM and was last modified in March 2014. Moreover, this section is not specifically for energy storage, it is meant for all fuel types.

For fuel source changes or energy storage technology type changes, a restudy should be performed. The PTO should submit a Study Plan for CAISO approval before performing the restudy.

PG&E Comment 1, Question 3: “Wouldn’t any energy storage addition or replacement, by its nature, affect an intermittent resource’s NQC?”

Yes it will. In this way energy storage is analogous to installing more inverters than the approved interconnection capacity. As discussed in PRR 825 and incorporated in this BPM on April 30, 2015, the CAISO determined that providing flexibility for developers to have back-up facilities to ensure they are meeting their power purchase agreement requirements outweighed the minimal impact to NQC so long as the project output cannot exceed what was originally studied.

PG&E Comment 2: How does this work if the project is Energy Only?

As an energy only project, the total MW output studied will equal the interconnection amount. As an example, a 100 MW energy-only wind project that wants to change to solar PV could install 100 MW energy only solar PV.

This particular example requires a limited restudy with its own study plan and schedule. Please see above for our proposed changes.

PG&E Comment 4: The description of the options that follow do not make entirely clear how they options differ. More clarification would be appreciated.

Option 1 is for a partial MW replacement (e.g., a 100 MW solar PV project wants to decrease to solar PV to 80 MW and put in 20 MW of storage). Option 2 is an energy storage addition (e.g., a 100 MW solar PV project adds a 20 MW storage unit, but the output to the CAISO controlled grid is limited to 100 MW or 90 MW assuming the 90% exceedance factor).

PG&E Comment 5: What is the exceedance factor that the CAISO will use for storage projects? E.g., a melded or pure storage with no BTM charging source (PV for example) can change the capacity at which DNU studies were done.

The CAISO uses an exceedance factor of 100% for storage. The storage portion of the project will be required to be metered and telemetered separately.

PG&E Comment 6: Capacity at the POI without energy storage is 0 to pmax. Unless the storage project is getting charged by a BTM source, it would change the capacity from a Pmin of 0 to the max charging MW. If the intent is to allow the capacity at poi to change, then this language should be revised. In such cases, charging studies will need to be performed.

In it’s recommendation, the CAISO revised the reference to read “maximum capacity at the POI”, but disagrees that charging studies need to be performed because charging is negative generation and not firm load. This issue was addressed in the Energy Storage stakeholder process in 2014. The Draft Final Proposal can be foundat:

Not performing a charging study exposes the PTOs to potential voltage and transient issues caused by the charging mode of the storage.

In addition, the proposal specifically addressed the modification process to add storage. The process consistent with the CAISO tariff is:

6 Modifying projects to include storage

The ISO recognizes that developers may want to modify their projects to add storage. The purpose of this section is to clarify how two existing processes—the Material Modification Assessment and the modification review—can be used to accommodate such requests, including behind-the-meter changes. The Material Modification Assessment (MMA) and modification review processes are very similar. MMA is provided in Section 4.4 of Appendix U, Section 6.9.2 of Appendix Y (GIP) and Section 6.7.2 of Appendix DD (GIDAP). The modification review process is provided in Article 5.19 of the LGIA and Article 3.4.5 and 6.2 of the SGIA. In both cases, the interconnection customer requests an assessment to modify their project, the modification is evaluated by the ISO and PTO, and the interconnection customer is charged the actual cost of the assessment; however, the process to get to the result is slightly different. In the case of a project in the queue that has not achieved their final commercial operation date, in accordance with Appendix U, Y or DD, the customer submits an initial $10,000 deposit. If the project has already achieved their final commercial operation date, then a request is made in accordance with their executed agreement to and the customer is billed after-the-fact for the study. The other difference between the MMA and modification review is the criteria used to determine whether a requested modification is approved. These scenarios and the appropriate process steps are described in greater detail below.

As a next step following this initiative, the ISO will consider which of the clarifications contained in this section on modifying projects to include storage may be appropriate to reflect in the Business Practice Manual for Queue Management.

6.1 Projects in the interconnection queue

This section addresses modification of projects in the queue (i.e., under the provisions of the serial study process, the generator interconnection procedures (GIP), or the generator interconnection deliverability and allocation procedures (GIDAP)) based further on whether or not the project has achieved the project’s final commercial operation date.

6.1.1 Pre-COD

If the project in the queue has not yet achieved final commercial operation date (i.e., it is pre-COD) and the customer wants to modify its project, then the ISO would use the Material Modification Assessment process. A change is deemed to be material if the modifications have a material impact on the cost or timing of any interconnection request or any other valid interconnection request with a later queue priority date. If not material, then the modification is approved. If material then the project must submit a new interconnection request. The following options can be considered:

  • For projects seeking full capacity deliverability status (FCDS) above the original project’s FCDS amount, one of the following two options may be used:
  • Submit a new FCDS interconnection request in the next cluster study open window.
  • Submit an ISP interconnection request if the project can meet the independent study process (ISP) technical and business eligibility criteria. This can be submitted at any time of the year with the FCDS being studied during the next cluster’s Phase I and Phase II deliverability studies.
  • For projects that do not seek to exceed the original project’s studied FCDS amount, one of the following three options may be used:
  • Submit a new energy-only (EO) interconnection request in the next open window for the cluster study process.
  • Submit an EO ISP interconnection request (any time of the year) if the project can meet the ISP technical and business eligibility criteria.
  • Submit an ISP behind-the-meter (BTM) interconnection request if the project can meet the ISP BTM technical and business eligibility criteria (any time of the year). An automatic tripping scheme will be needed for any capacity above the original project’s capacity.

6.1.2 Post COD

If the project has achieved its commercial operation date (i.e., it is post-COD) and the customer wants to modify its project, then the project would request a modification review. The ISO would approve the modification request if the total capability of the project is equal to or less than its existing capability and the electrical characteristics are substantially unchanged. If the ISO does not approve the modification request, then the project must submit a new interconnection request. The following options could be considered:

  • For projects seeking FCDS above the original project’s FCDS amount one of the following two options may be used:
  • Submit a new FCDS interconnection request in the next cluster study open window.
  • Submit an ISP interconnection request if the project can meet the ISP technical and business eligibility criteria. This can be submitted at any time of the year with the FCDS being studied during the next cluster’s Phase I and Phase II deliverability studies.
  • For projects that do not seek to exceed the original project’s studied FCDS amount one of the following three options may be used:
  • Submit a new EO interconnection request in the next open window for the cluster study process.
  • Submit an EO ISP interconnection request (any time of the year) if the project can meet the ISP technical and business eligibility criteria.
  • Submit an ISP BTM interconnection request (any time of the year) if the project can meet the ISP BTM technical and business eligibility criteria. An automatic tripping scheme will be needed for any capacity above the original project’s capacity.

6.2 Projects already approved for repowering

This section addresses projects that have been approved for repowering and want to further modify their project either before the repowered project achieves final commercial operation date or after the repowered project achieves the final commercial operation date. If the total capability is equal to or less than existing capability and the electrical characteristics are substantially unchanged, then the modification is approved. If the modification is not approved, then the project must submit a new interconnection request. The following options can be considered:

  • For projects seeking FCDS above the original project’s FCDS amount one of the following two options may be used:
  • Submit a new FCDS interconnection request in the next cluster study open window.
  • Submit an ISP interconnection request (any time of the year) if the project can meet the ISP technical and business eligibility criteria, with the FCDS being studied during the next cluster’s Phase I and Phase II deliverability studies.
  • For projects that do not seek to exceed the original project’s studied FCDS amount one of the following three options may be used:
  • Submit a new EO interconnection request in the next open window for the cluster study process.
  • Submit an EO ISP interconnection request (any time of the year) if the project can meet the ISP technical and business eligibility criteria.
  • Submit an ISP BTM interconnection request (any time of the year) if the project can meet the ISP BTM technical and business eligibility criteria. An automatic tripping scheme will be needed for any capacity above the original project’s capacity.

PG&E Comment 7: Will the CAISO evaluate FCDS storage requests, but will not evaluate a change to the deliverability status through the MMA process? Please confirm that this revision allows for an existing FCDS project to add storage, and how.

If an existing FCDS project wants to add storage to its project, its ultimate total amount of FCDS capacity will depend upon whether the storage can meet RA requirements and the ultimate structure of the project, as detailed in the new table in section 6.5.3 of the BPM..

PG&E Comment 8: Does this mean that the storage project will be separately metered so that, post COD, it does not influence or change the yearly NQC calculation at the site?

Yes, it will be separately metered but the NQC will change as discussed above.

PG&E Comment 8: While there is no definition of “substantially unchanged” in the portions of this BPM that are reproduced here, the general language treating of substantial changes is confusing for deciding what process is established to approve post-COD modification process requests. If the process is through an MMA, there should be criteria for this in section 6.5.3 to deem a requests as material or not. If the language refers to Section 25.1.2, then there should be a direct reference to the tariff section.

This is a direct quote from the tariff and the reference is already made in the paragraph that included the quote. The CAISO details what constitutes a substantial change in Section 25.1(c) of the tariff and Section 11.2 of this BPM. Section 11.2 address repowering, where these situations occur most frequently, but the tests would be substantially the same.

For PG&E’s comment 10, please see PG&E’s suggestion in comment 6. “Not performing a charging study exposes the PTOs to potential voltage and transient issues caused by the charging mode of the storage.”

PG&E Comment 11: During charging and discharging mode, the .95 power factor at the POI requirement needs to be met. If the study results do not show the need, then the energy storage project should meet unit power factor requirements at its POI.

The power factor requirements for each project is included in the Generator Interconnection Agreement (LGIA Section 9.6.1 and Appendix H, SGIA Section 1.8.1 and Attachment 7).

The LGIA and Appendix H/SGIA and Attachment 7 do not specify the power factor requirement but refer to the study report.

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[1] The conclusion of the process was as follows : “The ISO is committed to helping facilitate the development of energy storage, and through this energy storage interconnection initiative has been working with stakeholders to assess whether any potential policy and process changes to existing ISO interconnection rules are needed to accommodate storage. Through this effort an approach was developed whereby existing tariff rules can accommodate the interconnection of storage to the ISO controlled grid without the need for tariff changes. Key to this approach is that storage projects are treated as generators for both aspects of their operation. This means that a storage resource is treated as a generator that produces positive energy (i.e., positive generation) during discharge mode and negative energy (i.e., negative generation) during charge mode. This is consistent with how storage is presently treated in ISO markets under the non-generator resources (NGR) model. In addition, just like conventional generation, the resource must respond to ISO dispatch instructions, including curtailment to manage congestion. In the context of storage, this would apply during both discharge and charge modes. This approach is limited to grid-level interconnections of stand-alone storage and storage combined with generation, but not storage combined with load. The existing GIDAP provisions will not be utilized to assess requests by storage projects to obtain a higher level of service for their charging functions (i.e., comparable to firm load service). The GIDAP study process and cost responsibility framework do not apply to firm load. If a storage resource requests interconnection to the ISO controlled grid but does not want to respond to ISO dispatch instructions during charge mode, then it must seek such firm load service from the appropriate participating transmission owner through its existing load interconnection process”