Chapter VI Key Takeaways

In Chapter VI: Improving Grid Transparency Through Hosting Capacity Analyses and Other Tools, the Toolkit focuses on how grid transparency tools such as pre-application reports and hosting capacity analysis (HCA) can enable applicants to access information prior to submitting an interconnection application. Chapter VI also discusses how the HCA might be used in the interconnection process itself to help evaluate interconnection requests.

Recommendations for Improving Grid Transparency Through Hosting Capacity Analyses and Other Tools:
1. Utilities should provide data on the state of the distribution system at the Point of Interconnection through pre-application reports and basic distribution system maps. Chapter VI provides a list of the information fields most commonly requested by developers. This information includes, for example, existing and queued generation, load profiles, and distribution system lines maps. Chapter VI also describes how customers can use distribution system data to help inform project site selection and ESS system design and installation.
2. HCA can serve as an informational tool to guide ESS design. For example, developers can use HCA results to design their ESS systems to avoid contributing to grid constraints by limiting charging during existing net peak load hours. To enable such use of HCA, regulators, developers, and utilities must take several important considerations into account. These include the fact that hosting capacity values on a map provide a snapshot in time and often correspond to a specific DER technology and associated control, and that they may not capture the latest grid or DER queue data because projects in the queue are considered tentative until interconnected.
3. HCA can also serve as a decision-making tool in the interconnection review process for ESS. For example, California has required the use of HCA (called Integration Capacity Analysis in California) results instead of the 15% screen, which evaluates if total generation on a feeder exceeds 15% of a line section’s peak load. Current HCA methods implemented by utilities cannot by themselves replace the entire screening process. However, they could help enable ESS to be designed in ways that address specific grid constraints and enable more efficient and cost-effective DER interconnection. To unlock such benefits, HCAs would need to provide hourly information about grid constraints. Potential benefits would need to be weighed against the limitations of such an analysis to lock in an ESS design as well as the costs to develop and maintain these complex analyses of hourly grid constraints.

A. Introduction and Problem Statement

Storage can provide energy to, and charge from, the grid in a controlled manner that avoids or minimizes the need for upgrades while providing valuable grid services. However, to optimally design storage to provide these benefits, access to information about the distribution grid and its constraints is needed to inform where and how to interconnect storage.

Currently, the information about distribution grid equipment and constraints that is needed to select sites and design site-specific operating profiles is largely inaccessible to those looking to install storage. Limited information around distribution system needs and constraints forces customers to submit interconnection applications and operating profiles for projects that may not be properly tailored to a grid location. The evaluation of interconnection applications for ESS that are not optimized for their grid location results in wasted time and resources for both the interconnection customer and the utility. In addition, areas of the grid that can benefit from storage services may receive less focused attention or poorly designed projects. For these reasons, limited grid transparency is a barrier both to realizing the benefits of ESS for the grid and to ESS interconnection.

Utilities’ distribution system information is typically available to customers only through mechanisms that interconnection procedures or regulatory orders require. This toolkit provides stakeholders insights into information transfer options. It addresses practical methods and related requirements for the provision of distribution system data to ESS customers.

Hosting capacity analysis (HCA) is a complex analytical approach that uses power flow simulations to evaluate how the distribution grid performs with the addition of new DERs. It is a modern procedure that provides detailed and sophisticated distribution system analyses to utility engineers, customers, and state regulators. When HCA results are provided on an hourly basis, developers can use them to guide the design of ESS sizing and operation to avoid negative impacts on the grid and provide energy and other services when grid constraints allow it. In addition, if the HCA is used in the interconnection process, it can help screen for potential grid impacts caused by a proposed ESS project, facilitate more efficient application processing, and encourage better system design. There is some disagreement among stakeholders on how much an HCA analysis can be relied on to precisely design ESS operating profiles or to make decisions in the interconnection process; those points of disagreement are discussed further in the Recommendations section below.

Less sophisticated tools, including pre-application reports and “basic distribution system maps” that provide fixed grid data (and thus differ from HCA maps, as described above), are more commonly used today. However, for energy storage projects to provide many of their most valuable grid services, developers would benefit from more information than has typically been shared in the past for solar-only projects. This chapter first discusses how to use the less complex approaches available today and then how to adopt HCAs as a more granular and sophisticated tool that estimates time-varying grid constraints.

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