Chapter IX Key Takeaways

Energy storage can operate according to a predetermined schedule that includes both the total amount of power imported and exported as well as when the import or export occurs. This capability is not yet adequately addressed by interconnection standards or procedures. Chapter IX: Defining Rules and Processes for the Evaluation of Fixed-Schedule DER Operation discusses what steps need to be taken to establish the capability of devices to reliably control import and export according to a schedule. Chapter IX also discusses how those schedules should be communicated to the utility and how they can be evaluated.

Recommendations for Defining Rules and Processes for the Evaluation of Fixed-Schedule DER Operation:
1. Standards should be developed that describe the scheduling of energy storage operations, especially time-specific import and export limitations. UL 1741, the primary standard for the certification of inverter functionality, should be updated to address scheduled operations. In addition, it may be desirable to update the testing procedures specified by IEEE 1547.1 or other standards to validate operation in compliance with scheduling requirements for non-inverter or non-PCS systems. Other standards could potentially be developed as necessary to support scheduling apart from IEEE 1547 and 1547.1.

2. Although regulators do not have direct control or authority over the standards development bodies or processes, regulators can create a sense of urgency and expectation, such as by beginning to incorporate scheduling functionality into interconnection rules with implementation dates set based upon standard publication. Regulators can also allow the use of equipment that conforms to proposed or draft standards. Finally, regulators can support the development of standards by convening working groups to discuss the use of DER schedules and the associated interconnection rules and requirements.

Because standards often take years to be developed, Chapter IX recommends several interim measures:
3. Regulators could actively develop or encourage the development of field test programs to validate the performance of a deployed system to a fixed operating schedule or profile.
4. Regulators can also help to inform the standards development process, while creating a more immediate pathway for scheduled operation of ESS in their state, by developing their own interim testing protocol that can be applied while national standards are under development.
5. With or without any of the verification strategies described in Chapter IX, monitoring for compliance with a schedule can be achieved with equipment that is commonly available today. Chapter IX describes several such monitoring mechanisms.
6. While standards are being developed, vendor attestations may be an avenue to provide utilities with some performance assurance. This is the simplest method of verification and manufacturers that have compliant products can likely turn around signed attestations in much less time than typical certifications through national testing labs, although there are risks associated with this approach.
Chapter IX also discusses the development of methodologies for the efficient evaluation of storage with proposed operating schedules:
7. To start studying complex fixed operating profiles in the context of time-specific feeder conditions, it will be necessary for some utilities to collect granular feeder load data for comparison with the proposed operating profile. The data can come from many sources, including advanced metering infrastructure, substation metering, Supervisory Control and Data Acquisition (SCADA), distribution transformer metering, billing departments, or other sources.
8. In addition to addressing utility data needs, the techniques for screening and studying projects with operating schedules require further development. In order to enable storage to provide valuable time-specific grid services, regulators should either proactively convene working group discussions or encourage others to do so in order to work through the various issues with utility and DER stakeholders.
Finally, Chapter IX discusses establishing standardized formats for communicating operating schedules:
9. Regulators should convene a process to establish a standard template for the communication of operating profiles. They will need to consider which data points are necessary based upon the ways utilities will actually study projects. Chapter IX includes a sample template that can serve as a starting point.

A. Introduction and Problem Statement

Defining and verifying export controls is a critical foundation for energy storage, but it is not all that is needed to enable customers and the grid to capture arguably the greatest benefit of ESS: its schedulable and dispatchable nature. Many electric system impacts have a temporal aspect to them due to both daily and seasonal changes in the load curve and the prevalence of generating resources (e.g., solar or wind) that operate during certain times of the day or have seasonal output variations. Energy storage is unique among inverter-based resources in its ability to provide or consume energy at any time.

ESS may be designed to operate on a schedule or to respond to dynamic signals for a variety of reasons (e.g., customer needs, rate schedules, market participation, or to avoid distribution system constraints). However, today the default method for conducting an interconnection analysis is to study projects in a manner that assumes the project may export or import its full capacity at any time. In some cases, utilities are able to take into account that solar systems only operate during daylight hours, but there is very little nuance beyond that in terms of hourly, daily, or seasonal variations, or variations in output quantity. Unfortunately, the existing rules and methods often complicate or prevent the interconnection of storage on constrained infrastructure where ESS could be most beneficial.

The following two terms will be used to describe the scheduled operation in this chapter:

Operating Profile means the manner in which the distributed energy resource is designed to be operated, based on the generating prime mover, Operating Schedule, and the managed variation in output power or charging behavior. The Operating Profile includes any limitations set on power imported or exported at the Point of Interconnection and the resource characteristics, e.g., solar output profile or ESS operation.

Operating Schedule means the time of year, time of month, and hours of the day designated in the Interconnection Application for the import or export of power.

Analysis of a resource operating continually at full capacity—an impossible scenario for energy storage which must charge at some point—may lead to unnecessary and time-consuming studies or costly upgrades, and can impair the ability of applicants to propose projects that are targeted at resolving specific system needs or providing necessary services. To realize the full value of ESS, it will be necessary to create or modify interconnection rules and processes such that time-specific operations are enabled. This includes the ability to interconnect on the basis of scheduled operation in locations where nonconformance to an operating schedule would have adverse impacts. Unfortunately, unlike the other barriers discussed in this Toolkit, there is a considerable amount of additional research, evaluation, and analysis needed before concrete solutions can be recommended.

The BATRIES team has identified three areas where critical work and resources need to be developed to facilitate the safe and reliable evaluation of DERs operating with fixed schedules:

  1. Identify methods of providing utilities with assurance that ESS can safely and reliably conform to a fixed schedule. Just as utilities need to have confidence that the export control technologies discussed in Chapter III are reliable, they will also need to be able to trust the scheduling functionality.
  2. Determine how utilities will screen and study projects that are utilizing reliable scheduling methods. This requires better understanding of what the current utility capabilities are, what the data needs are, and what new methods or approaches can be used to efficiently evaluate operating schedules of varying levels of complexity.
  3. Define how interconnection applicants should communicate their proposed operating schedule to the utility with their application. This may include developing standardized templates for data transmission based upon the complexity of the schedule and the utility’s data needs.

This chapter outlines these essential areas of development that are needed to allow for evaluation and implementation of fixed schedule operation of ESS. It provides recommended actions regulators can take to accelerate the development of both near- and long-term solutions. The chapter points to further opportunities to implement dynamic controls, but primarily focuses on fixed schedule operation.

Download the chapter file below to read more. Or download the full Toolkit and Guidance for the Interconnection of Energy Storage and Solar-Plus-Storage for all chapters and recommendations.


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