C. Developing Methodologies for Efficient Evaluation of Energy Storage Projects with Proposed Operating Schedules
While the development of standards and/or other means for providing utilities with assurance that ESS can reliably perform according to operating schedules is a critical step, this alone does not resolve the fundamental question of how projects with operating schedules will be evaluated in the interconnection process. To date, very little has been done to explore how utilities will evaluate the potential impacts of projects that are proposed with an operating schedule or any type of operating profile. Significant gaps exist in terms of understanding existing utility capabilities, data needs, and methods that can be used to efficiently, and cost-effectively, screen and study projects using operating profiles. The grid benefits of schedulable ESS cannot be realized if utility screening and study processes do not evolve to accurately evaluate operating schedules, thus it is critical for regulators to facilitate development in this area. Promoting pilots to allow energy storage to be interconnected on a non-traditional study basis where storage functionality is used to avoid negative grid impacts in place of upgrades is a recommended way forward.
1. Utility Data Needs for Evaluating Operating Profiles
Because scheduling capabilities are relatively new, are not yet supported by standards, and the need for scheduled services has not been acute in the past, utilities generally conduct the screening and study process assuming that projects will be operating at full capacity 24 hours a day, 365 days a year. In the case of solar-only projects, the penetration screens (see discussion in Chapter IV.C.3.a.i) and the study process can take into account that the project will only operate during daytime hours, but this is different than evaluating a true schedule. It is important to recognize that since utilities assume consistent operation, they are able to conduct studies using relatively limited grid data currently. In essence, many utilities may be evaluating projects using only the absolute recorded minimum and peak loads on a feeder. This means that the utility effectively needs to run only a single iteration of the power flow analysis to determine if a project will cause system impacts at any point during a year.
When it comes to evaluating a project using a more nuanced operating profile, utilities are likely to need access to grid data for more hours of the day and year, and may also need to develop new methods for running power flow models so that evaluations of operating profiles can be conducted efficiently.
The exact data needs and study capabilities and techniques will vary based upon how complex of an operating profile is being evaluated. For example, if a solar-plus-storage project is proposing to simply extend the hours of operation into the evening hours and can propose a fixed operating schedule that corresponds to these hours, the technical evaluation can be conducted in essentially the same manner as it would be for a solar-only project, with the minimum load only being selected from a wider range of hours. Similarly, if an ESS project is proposing to not export to the grid during periods of low demand (i.e., between 12-3 pm when solar generation may be abundant in certain states), the minimum load can be selected during just the proposed hours of operation.
However, studies—and corresponding data needs—get more complex when operating schedules contain multiple different operating periods. For example, if a project proposes to utilize a seasonal operating schedule, there may be a maximum output period for each season and thus there may need to be more than one minimum load hour evaluated. The complexity can continue to increase, including variations during different days of the week, months of the year, and different export amounts (output), up to the point where there is a different operating point for each of the 8,760 hours of the year. As the schedules increase in complexity, so too will the utility’s data needs in order to be able to accurately evaluate how the varying output corresponds to different grid conditions during those hours.
There is considerable variation across the country in the amount of data that utilities collect and can readily access. Some utilities do not presently collect, warehouse, or publish hourly feeder data for interconnection purposes, but others have access to considerably more data for a variety of uses, including for interconnection, hosting capacity analysis, and other grid operational needs.
To start studying complex 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 to the proposed operating profile. On the other hand, it may be possible for many utilities to start evaluating projects with simpler operating profiles immediately while further data is collected and study processes are refined.
This data can come from many sources. These sources may include, but are not limited to, advanced metering infrastructure (AMI), substation metering, SCADA, distribution transformer metering, billing departments, etc. This data can be further processed for better load modeling if needed.((Xiangqi Zhu and Barry Mather, Data-Driven Distribution System Load Modeling for Quasi-Static Time-Series Simulation (Sept. 10, 2019), https://www.osti.gov/pages/servlets/purl/1606307.)) Additional methods of capturing this hourly data through distributed energy resource management systems (DERMS), advanced distribution management systems (ADMS), DER communications such as IEEE 2030.5, etc. may also need to be investigated and developed by industry stakeholders where rapid and ubiquitous AMI deployments are cost prohibitive.
2. Defining Screening and Study Techniques for Operating Profiles
In addition to addressing utility data needs, the techniques for screening and studying projects with operating profiles require further development as well. Transitioning from comparing a project to a single minimum load hour to comparing it to multiple different temporally-specific periods requires consideration of the most efficient method for conducting the analysis, the computing and technical resources required, and the manner in which the results will be communicated to customers. As discussed above with respect to the data needs, the complexity of the studies will vary based upon the nature of the proposed operating profile.
a. Using Hosting Capacity Analyses to Evaluate Proposed Operating Profiles=
One method for screening projects with operating profiles that regulators may want to consider is the utilization of detailed hosting capacity analyses. When hosting capacity analyses are conducted using granular hourly profiles (e.g., 576 hours per year or more), they can provide a detailed “hosting capacity profile” that shows for each hour evaluated what the hosting capacity limit is for each technical criteria evaluated. If the analysis is conducted with high-quality, granular data and is updated frequently, it has the potential to dramatically simplify the process for screening projects with operating profiles. Projects could be allowed to interconnect without the need for customized power flow analyses so long as their proposed profile is below the hosting capacity limit for every hour evaluated in the analysis. Chapter VI.B.2.b discusses this option further, describes the steps that California has taken in this direction, and also details the reservations that some stakeholders have about utilizing hosting capacity analyses in the screening processes.
3. Recommendations
At present, discussions regarding evaluation of operating profiles are just beginning to occur in the U.S. and there have yet to be comprehensive papers, best practices, or guides drafted to inform regulators on how to conduct these analyses. As of this writing, few jurisdictions appear to have established guidelines for interconnecting ESS with an operating profile. Identified efforts led by Massachusetts are preliminary and, based on project research, no schedule-based interconnections have been allowed to date. In order to move this capability forward and enable ESS to provide valuable time-specific grid services, it is recommended that regulators either proactively begin to convene working group discussions or encourage others to do so in order to work through these issues with utility and DER stakeholders. Some outside bodies (e.g., the National Association of Regulatory Utility Commissioners, the U.S. Department of Energy, etc.) could help move the conversation forward.
Specifically, regulators should seek to have utilities identify what data they have available and what additional data they believe they may need to evaluate a range of different operating profiles. They should also outline what methods utilities intend to use to evaluate projects with proposed operating profiles. Armed with this information, a working group can determine what changes to the interconnection procedures may be necessary and also what data or capabilities may need to be acquired to facilitate an efficient evaluation of ESS with operating profiles. As discussed more below in Chapter IX.D, these discussions can also help determine what information, and in what format, applicants should provide to utilities about proposed operating schedules. If the necessary data or capabilities for a full evaluation of sophisticated operating profiles does not exist, the working group can evaluate steps to allow for evaluation of simpler profiles in the near term. This work can be conducted concurrently with the standards or other schedule assurance processes outlined in Chapter IX.B.1.a and IX.B.2.
