D. Establishing Standardized Formats for Communication of Operating Schedules
The final area that requires attention in order to facilitate the interconnection of ESS with fixed operating schedules concerns how those schedules will be communicated to the utility for evaluation. For utilities to be able to evaluate the interconnection application of an ESS with a proposed operating schedule, the applicant will need to provide detail about the project’s operating profile in a format that aligns with how the utility will be evaluating the project.
The project team surveyed several utilities across states typically engaged in progressive interconnection rulemaking, including California, New York, and Massachusetts. While none of the utilities surveyed are at the stage of conducting analyses that lead to binding interconnection agreements based on proposed schedules, some are at least starting to consider how information on schedules should be provided.
Where they exist, schedule submission guidelines vary. For example, the NY Standardized Interconnection Requirements (SIR) Appendix K simply states: “Indicate any specific and/or additional operational limitations that will be imposed (e.g. [sic] will not charge between 2-7pm on weekdays)”.((National Grid, Upstate NY Form K, https://ngus.force.com/s/article/Upstate-NY-Form-K.)) The Massachusetts process is more refined and was developed through a series of collaborative meetings between the utilities and key stakeholders. This effort resulted in the development of a standardized worksheet, shown in Figure 11, which some of the collaborating stakeholders proposed for use as a template for the submittal of an operating schedule.((MA Dept. of Pub. Util. Docket 19-55, Inquiry by the Department of Public Utilities on its own Motion into Distributed Generation Interconnection, Collaborative Process Filing, Consensus Document B (Oct. 13, 2020), https://fileservice.eea.comacloud.net/FileService.Api/file/FileRoom/12771446.)) The Massachusetts Department of Public Utilities had previously approved the use of a more simplified worksheet and has yet to formally adopt the proposed updated worksheet, but it is a useful example nonetheless.((MA Dept. of Pub. Util. Docket 19-55, Hearing Officer Memorandum: Interim Guidance – Energy Storage Systems, ESS Questionnaire (Dec. 3, 2019), https://fileservice.eea.comacloud.net/FileService.Api/file/FileRoom/11510272.))
In addition to the table shown above, New York and Massachusetts utilities currently request that applicants provide a free-form description of the use cases and other characteristics of the operating profile. Such methods are likely to elicit responses including undefined use cases, non-uniform times, or other features that are subject to interpretation and not conducive to uniform or automated study processes. For utilities to use such free-form responses in an automated study process, it would need to be translated into a software-compatible format. Additionally, developers and utilities would have to align on use case definitions and other factors. The gap between these free-form responses and a template that could be directly used by automated study processes has been identified as an opportunity for development.
1. Taxonomy Working Group Template
In 2021, EPRI convened the Energy Storage Functional Taxonomy Working Group.((Electric Power Research Institute, Energy Storage Functions Taxonomy Working Group (June 3, 2021), https://www.epri.com/research/programs/067418/events/93B041AC-D90B-4F0E-B9D5-8EDA6439A33F.)) The goal of this working group is to develop a common understanding of ESS terms and a template that can be used to communicate a complete operating schedule at the time of interconnection for any proposed energy storage project. The goal is to help to streamline interconnections and reduce workload as the quantity of deployed DERs continues to rise. The operating schedule under development will contain information regarding what the storage is doing, when it is intended to do it, and perhaps most importantly, what import and export limits are in place at what times. It is intended that this information can be communicated in a single spreadsheet format that can prevent the utility from needing to manually translate it to an electronic format.
As part of the taxonomy effort, the group is developing a template, shown in Figure 12, to communicate these datapoints in an hourly format that could be used directly by automated study processes. The goal of this template is to provide a normalized format that can enable streamlined future interconnections that account for the unique capabilities of storage, such as operating to a schedule, and/or in accordance with import and export limitations. Since this working group is ongoing at the time of this writing, the template is likely to evolve.
The template proposes an hourly operating schedule, and could be adapted to a shorter or longer time interval as needed. Hourly scheduling is currently recommended by the working group as most tariffs with time-of-use components or other peak times typically use whole-hour times. Use of an 8760-hour schedule is recommended as hourly load data will be stored in this format and because many tariffs include weekends, seasonal changes, holidays, and similar features that could affect system operations.
The second and third columns describe import and export limitations by percentage of either system nameplate or total facility rating. These import and export limit columns provide the critical information that describes a scheduled system’s capability to respect time-specific hosting capacity issues. Subsequent columns describe the use cases and how each use case is related to the next. This is useful for understanding the likely behavior of a proposed system.
As an example, the sample template shown below depicts a purely theoretical customer storage system that would normally operate in self-consumption mode but can provide demand response during afternoon peak hours. The sample system is configured to be able to export only during demand response events. During that time, import or charge is disabled to prevent it from adding to peak demand.
The list of use cases below is provided as an example. In cases where multiple use cases are intended, such as time-of-use support with a secondary use case of backup power, a secondary or even tertiary column may be used to express the alternate use case. The hourly import and export limits are the items of primary interest for interconnection needs today. However, the communication of what use case(s) the storage will engage in can aid future modeling and study efforts. A column between the primary and secondary use cases provides a description of the relationship between use cases. In the sample, it suggests that the secondary use case is engaged by a grid outage. Other example descriptors of relationships between use cases could include “dispatched,” “simultaneous,” “price signal,” and others.
Figure 12. Sample Operating Schedule Template and Applicable Use Cases
|Sample Use Cases|
|RE Firming |
Demand Charge Management
This template is intended to communicate the import/export limits that comprise an applicant’s fixed operating schedule. Many stakeholders, however, have significant interest in the ability to dispatch energy storage. This dispatch may be for many purposes including grid support, market participation, or renewables integration, but the ability to model and study how dispatch of energy storage will impact the grid is presently lacking. The provision of hourly import/export limits can serve as guardrails to keep any potential actions dispatched by remote signals from directing the ESS outside of acceptable operating parameters for that specific time of day.
Regulators will need to convene a process to establish a standard template for the communication of operating profiles. While the final outcome of the Energy Storage Functions Taxonomy Working Group will be informative to this process, regulators will need to consider whether all of the information indicated above is actually necessary to provide based upon the manner in which utilities will actually study projects. A utility’s study capabilities will inform whether all the information indicated above actually serves any functional purpose in the interconnection review process. For example, it is not clear to all of the BATRIES project team members how detailed information on use cases in the interconnection application will actually be used if the utility is only ultimately going to analyze the amount the project imports or exports during each hour. Thus, regulators and utilities should work together to consider the requirements for communicating an operating schedule at the same time that the utility’s data needs and study process are evaluated as outlined above in Chapter IX.C. By considering these topics together, regulators and utilities can settle on an approach that facilitates safe and reliable interconnection of ESS while also not overburdening either the applicant or the utility with unnecessary data requirements. To this effect, regulators and utilities may want to consider whether the template and information requirements should vary based upon the level of complexity of an applicant’s proposed operating schedule and also whether they should evolve along with the utility’s study capabilities.