Chapter III Key Takeaways

In this chapter, the Toolkit provides recommendations to ensure that the method a storage system uses to control export is safe and reliable. This can be done by updating interconnection procedures to recognize the ability of ESS to control and manage export in a way that can mitigate or avoid grid impacts. Chapter III: Requirements for Limited and Non-Export Controls provides background on the different methods available for controlling export and pays particular attention to Power Control Systems. The chapter discusses how PCS work and the current standards development process for them (UL 1741 Certification Requirement Decision for Power Control Systems). The chapter also provides recommendations on how to recognize acceptable export control means in interconnection procedures. It proposes options for doing so in a manner that supports safety and reliability, while also increasing certainty for customers and minimizing the need for time-consuming and potentially costly customized reviews by the utility.

Recommended Requirements for Limited- and Non-Export Controls:
1. Relying on customized review of the export controls for every interconnection application is a significant barrier for ESS deployment. Non-standard types of export control equipment will continue to need customized review, but interconnection procedures should be updated to identify a list of acceptable methods that can be trusted and relied upon by both the interconnection customer and the utility. The recommended model language establishes that if an applicant uses one of these export control methods, the Export Capacity specified in the application will be used by the utility for evaluation during the screening and study process.  

2. For Power Control Systems specifically, in order to recognize the controllable nature of ESS in interconnection review, PCS should be included in the list of eligible export controls, and the limits set by the PCS should be considered as enforcing the Export Capacity specified in the application.  

3. The chapter provides six different acceptable export control methods, and a seventh export control option that allows for the use of any other method so long as the utility approves its use.  

A. Introduction and Problem Statement

Storage systems have unique capabilities, such as the ability to control export to, or import from, the grid. There are multiple different methods by which ESS can manage export, including the use of traditional relays as well as Power Control Systems that have recently been refined under a common standard. However, utilities, customers, developers, manufacturers, and regulators may be unfamiliar with the currently available control technologies and methodologies for testing or verifying that Power Control Systems will operate as intended. This can result in each ESS needing a tailored screening and study assessment to interconnect (known as customized review), testing, and/or utilities overestimating system impacts if they do not have confidence in the controls used. These are significant barriers to an efficient and effective interconnection process for ESS.

Energy storage export and import can provide beneficial services to the end-use customer as well as the electric grid. These capabilities can, for example, balance power flows within system hosting capacity limits, reduce grid operational costs, and enable arbitrage for solar-plus-storage owners via self-supply. But if mismanaged or enacted at the wrong times, these same capabilities can have adverse and potentially damaging effects.

For most grid assets, relays, circuit breakers, and manual disconnect equipment have been regularly employed as protection equipment to prohibit adverse operations. However, energy storage has inherent flexibility that presents unique opportunities for departing from status quo grid integration and protection approaches. For example, ESS offers an ability to dispatch active and reactive power via a PCS, a high rate of response, and the capability to transition twice its rated power in a single step (from full import to full export or vice versa). Developing standardized methods for validating the types of export controls most suited for ESS and other DERs can help take full advantage of ESS performance while also minimizing interconnection costs. Standardized methods are also essential for ensuring that utilities can provide reliable electricity, in part, through the reliable operation of interconnected assets.

Clear identification of standardized methods of controlling export in interconnection rules also provides interconnection customers the information they need to properly design ESS projects prior to submitting interconnection applications. This regulatory certainty reduces the time and costs associated with ESS interconnection by minimizing the amount of customized review needed and by empowering customers to design projects that avoid the need for distribution upgrades.

Today, many state interconnection procedures do not yet recognize export-limiting capabilities at all, and even fewer concretely identify the acceptable methods of control. The following chapter provides background on how interconnection procedures consider export limiting today. It introduces the types of export controls that can be used and discusses, in particular, the standardization process for PCS. It then provides recommendations on incorporating guidance on export controls into interconnection procedures to minimize customized review while also ensuring export-controlled systems are safely evaluated.

Note: While this chapter discusses the requirements for limited- and non-export controls, Chapter IV discusses the screening and study process for evaluating these types of systems.

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.