Utilities are faced with making decisions on how to consider this growing penetration of distributed energy resources (DER). The result is a new set of challenges for planning and operating the grid, especially on the distribution system that serves these new resources. With this change in mind, utilities across the country are beginning to look at how to meet this need.
In New York, the New York State Public Service Commission launched the Reforming the Energy Vision initiative aimed to more fully integrate and utilize DER with distribution planning and operations. The utilities are required to establish a structure for a transparent planning process in addition to identifying where DER can be best accommodated.
In Minnesota, the Minnesota Public Utilities Commission called for Grid Modernization efforts to be outlined by utilities with the objective of maintaining system reliability, improving efficiency, and enabling further customer choice. Through this effort, it was recognized that the planning process used today must be updated to meeting the needs of the future.
In California, the California Public Utilities Commission is requiring that utilities develop a Distribution Resources Plan that will enable the identification of where DER can be best integrated on the system.
In order to meet this change, there is a need for analytical methods that identify impacts of distributed resources in the electric system. A foundational element of planning the distribution system of the future is the capability to assess the ability of distribution systems to “host” DER capacity.
Hosting capacity is defined as the amount of DER that can be accommodated without adversely impacting power quality or reliability under existing control configurations and without requiring infrastructure upgrades.
The range of DER a feeder can host depends on the location and characteristics of both the feeder and DER. Hosting capacity will change over time as load, DER and circuit configurations changes.
The concept of hosting capacity is not new, but the uses of it are becoming more widespread as the industry needs a comprehensive approach to understanding the impacts of DER.
Hosting Capacity Applications
The hosting capacity analytics and resulting visualizations can inform stakeholders and enhance utility decision making for multiple processes. The main application is to identify how much DER can be accommodated, what issues arise, and assess integration solutions to mitigate the issues. The hosting capacity calculations of the feeder can be overlaid with maps to inform developers of locations where issues are more likely to arise. See Figure 1 as an example. Additionally, it can be used to assist with interconnection screening and planning decisions.
Informing the Public: As DER interconnection queues grow across the country, there is a need to provide developers and customers with greater visibility into where on the system interconnection applications may require additional cost to be accommodated. Utilizing hosting capacity calculations to generate heat maps of the distribution system gives developers the ability to understand better/worse locations for DER on the system, how that aligns with locations they have identified as well suited for DER installation, and an initial indication of potential costs.
Assisting with Interconnection Technical Review: With increased numbers of DER interconnection applications and growing queues, there is greater focus on the ability to perform technical review of sites quickly and accurately. Hosting capacity can play a role in informing this process and help utility engineers in decisions on approval or need for further study. It is in this supplemental screening step that hosting capacity can inform the assessment made by the engineer. The hosting capacity calculations would provide information regarding the remaining amount of DER the feeder can host at a particular node and the limiting factor that may result in need for mitigation.
Enabling Planning with DER: Hosting capacity is an important part of scenario planning used to evaluate different what-if cases for DER. It can be enhanced with load and DER forecasts to evaluate planning scenarios on a feeder-by-feeder basis and quantify a range of potential future impacts. Under these scenarios, utilities can evaluate mitigating factors, infrastructure upgrades, as well as a system-wide cost benefit assessments. In the future, this enhanced level of analysis will enable utilities to determine the ability of the distribution system to utilize services from DER (non-wires alternatives – NWAs), the impacts of DER on grid reconfiguration, operational strategies, and smart inverter technologies.
Hosting Capacity Methods: Effective and efficient means for evaluating the impact of DER is a necessary aspect of distribution engineering today. Instead of requiring specialized analysis and skillsets, new methods are being developed that utilize existing distribution planning tools, can be performed by existing distribution planning personnel, and use readily available data that most distribution planners have on hand.
While methods may vary today, it is EPRI’s view that the analytics around these methods will continue to evolve and hybrid approaches that capture the precision of iterative, the efficiencies of streamlined, and the impact factors that improve accuracy, will prevail.
EPRI is continuing to actively work in this area around the DRIVE tool and is working alongside utilities and vendors alike to implement this method within existing distribution planning tools. This is a first, but crucial step towards effectively integrating DER into the distribution system.
For further reading on hosting capacity, the reader is directed to the recent white paper describing the hosting capacity applications in NY State. Defining a Roadmap for Successful Implementation of a Hosting Capacity Method for New York State, EPRI, Palo Alto, CA: 2016. 3002008848
Jeff Smith, Program Manager
Distribution Operations, Planning, and Studies