Navigant Research Blog

Distribution Resource Plans: Integrated Capacity Analysis

James Hansell — August 24, 2015

As discussed previously, California investor-owned utilities recently submitted their inaugural Distribution Resource Plans (DRPs), establishing a framework for the integration of distributed energy resources (DER) into the existing electric grid. As adoption rates for rooftop PV generation, behind-the-meter storage, and electric vehicles (EVs) rise, it becomes increasingly important to determine the extent to which the distribution system can accommodate the newcomers. To this end, the DRP filings include an integration capacity analysis (ICA), providing utility estimates of the ability of each of their circuits to incorporate DER. One of the goals of this analysis is to improve the efficiency of the grid interconnection process by providing DER hosting capacity data to the general public and third-party providers.

Integration Constraints

Per the guidance of the California Public Utilities Commission (CPUC), the utilities collaborated and developed a common set of constraints on integration capacity. The distribution system is designed to operate below equipment thermal limits, maintain voltage within acceptable bounds, avoid compromising protection schemes, and function safely. Therefore, each circuit segment was evaluated to determine the maximum amount of DER that can be connected to the existing electric systems without violating these rules. Southern California Edison (SCE) performed this analysis on a set of representative feeders and extrapolated the results to its entire service territory while Pacific Gas and Electric (PG&E) studied each individual circuit. Navigant expects that the next iteration of the DRP filings will require individual circuit analysis. In addition, there are plans to extend the set of evaluated criteria, as well as include an assessment of hosting capacity during expected switching operations and abnormal conditions.

Integration Capacity Criteria

Fig 1 blog
(Source: Pacific Gas and Electric)

DER Profiles

Because each category of DER has its own effect on the grid, the utilities had to perform different calculations for each resource type. Each utility had a different approach for this task. SCE separated resources into load-reducing (PV and storage) and load-increasing (EVs and storage) resources, while PG&E considered the hourly profile of each resource type separately. As the integration metrics are driven by net load, using hourly load impact profiles for each resource type will be necessary to optimally perform the analysis in the future. San Diego Gas & Electric (SDG&E) notes that it will acquire customer demand profiles from its advanced metering infrastructure (AMI) and localized DER impact profiles in order to improve the locational granularity of its next ICA.

DER Profiles 

Fig 2 blog
(Source: Pacific Gas and Electric)

Streamlining Interconnection Processes

One of the requirements of the CPUC guidance on DRP content was consideration of the applicability of the ICA to Electric Rules 15, 16, and 21 governing EV and distributed generation interconnection requirements. Perhaps contrary to CPUC expectations, while the utilities each allowed that the results of the ICA could be used to inform the interconnection process, none allowed it to immediately replace any of the required screens for fast track analysis. An augmented iteration that includes fast-tracked circuits and estimates of locational value would strongly support the integration of distributed resources.

The approach to the ICA displays a consistent theme across the DRP filings. Despite organizing around the same principles, the outcome methodologies are different enough to portend plenty of alignment discussions heading into the 2017 filing period.

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