Conservation Voltage Reduction
Conservation Voltage Reduction (CVR) is commonly known as a subset of Volt-Var Optimization (VVO) and is considered a cost-effective measure for energy savings and peak demand reduction without the need of opting in by customers, unlike any other energy efficiency program. To activate CVR, the voltage across a distribution feeder operates toward the lower regulated voltages by coordinating the utility equipment, including the substation transformer load tap changers (LTC), voltage regulators, and capacitor banks.
According to the American National Standards Institute (ANSI) standard C84.1, the voltage boundary across the distribution feeder should be between 114 V to 126 V during normal operation[1]. Therefore, CVR operates effectively if the voltage band is maintained at the lower half (114 V to 120 V) of the C84.1 recommended voltage without causing any harm to the utility assets and customer appliances[2]. As the voltage operates at the lower end, the voltage-sensitive loads at the customer terminal consume less than the normal operation and achieve energy savings. A recent benchmarking paper has discussed the CVR efforts of 37 U.S. utilities[3].
To report energy savings to public utility commissions or study cost-benefit ratio to decide on further CVR deployment, the energy savings benefits of CVR need to be quantified through measurement and verification (M&V). Quantification of benefits is a challenging task because the CVR ON and OFF measurements cannot be obtained simultaneously. As the changes in other confounding factors (for example, temperature, season, and time of the day) profoundly impact load consumption, estimating the load deviation becomes an extremely complicated effort between CVR ON and OFF instants. On top of that, the quality of data being used in the analysis and its inherent noise can further complicate the process.
Do We Need a CVR M&V Standard?
The IEEE CVR M&V Standard Taskforce was tasked by the IEEE Volt-Var Working Group within the Power and Energy Society (PES) distribution subcommittee in October 2020 to study the need for an industry-accepted standard for CVR M&V data collection and management. The Taskforce comprised complementary expertise from electric utilities, technology developers, national laboratories, and academia. The primary motivation of this Taskforce is to find out the gaps in conducting M&V analysis across the industry, identifying the anomalies in data and their sensitivities to different types of methodologies, and recommending a path forward to work toward filling out the gaps.
A proper process will help utilities evaluate CVR implementation in a precise manner. The standard will complement the group's existing work, including the IEEE P1885 Draft Guide for Assessing, Measuring, and Verifying Volt-Var Control Optimization on Distribution Systems. The taskforce conducted an industry-wide survey on the current practices, problems, and need for having an established procedure, as discussed in the following sections.
Utility Surveys and Studies
A total of 30 individuals participated in the conducted survey. Participants were from utilities, consulting, academia, manufacturers/vendors, and national labs. Key takeaways from the survey are listed below:
1. All participants highlighted issues with data quality, including non-numeric/missing, interpolated, repetitive, and outliers data, as well as issues related to active CVR schedule. Because of not maintaining an active CVR schedule while running 24x7 operations and/or irregular cycling (deviation from regular on/off testing), data becomes uncorrelated, which makes the analysis erratic.
2. Participants pointed out the data gap created after the cleaning process and the need for reconstructing the missing data points.
3. Participants observed discrepancies while using different methodologies on the same dataset.
4. A majority of the participants believed that there should be an established procedure to conduct M&V in order to calculate a correct benefit-cost ratio, maintain regulatory requirements, streamline data treatment approaches, and select the CVR factor calculation methodology.
5. Different utilities have various levels of oversight from the commission, including, but not limited to, periodic updates on the CVR factor, penalty factor on the savings based on CVR schedule, whether — and how — a loss factor should be used to estimate customer savings. These make the evaluation process inconsistent.
By considering the survey responses, a comprehensive analysis was conducted using the data received from four utilities. The study results yielded the following observations:
1. Quality of datasets (that is, anomalous voltage and/or power data, interruption in CVR operation, irregular cycling) impacts the analysis on CVR benefits evaluation (that is, CVR factor, savings), regardless of the applied methodology.
2. Differences are observed in evaluation results using both cleaned and reconstructed datasets.
3. Detection of inaccurate CVR statuses can impact the CVR benefits analysis and any kind of data reconstruction process.
4. It is imperative to maintain the loading consistently to analyze the benefits accurately. Any temporary or permanent load shift can jeopardize the analysis.
5. There is no defined boundary on what would be considered an accurate CVR factor based on the pilot and program-level study from different utilities.
6. Data resolution has minor impacts on M&V analysis as noted in the survey feedback.
7. There is no validated assumption on how to impose constraints on data distribution to filter out extremely divergent data in any methodology.
Highlights
Utilities identify a lack of defined guidelines in selecting the methodology as a major challenge in CVR M&V. More than 70% of all surveyed participants believe that established M&V procedures will be helpful in developing a CVR business case, maintaining the expected benefits, meeting regulatory requirements, and streamlining the data cleaning process for benefit estimation. Also, more than 80% of all surveyed participants believe that an established M&V procedure will be helpful in selecting the methodology based on data availability.
The current state of the grid in CVR deployment, in which many utilities have rolled out CVR programs on hundreds of their feeders, further justifies that electric utilities are ready to adopt an industry-accepted standard to support their efforts. Based on the survey and studies, the Taskforce concluded that the industry needs a standardized data management practice (including cleaning, reconstruction, and analysis) that includes at a minimum:
- Identification of cycling schedule disruption and required cleaning.
- Standardization of compression rates to achieve true values.
- Detection of accurate CVR status.
- Detection of outliers.
- Identification of load shifts and how to deal with these in terms of measurement and verification.
- Data cleaning and reconstruction approaches for anomalous data.
- An approach to determine CVR factor range and system-level CVR factor.
- Determination of data adequacy based on accurate CVR status, power, and voltage data.
- Methodology selection and assumption validation based on data availability.
Next Steps
The Taskforce is working under the IEEE PES Volt-Var Working Group and currently comprises multiple volunteers from the industry, national labs, and academia. Taskforce members meet on a bi-weekly basis to discuss various sections of the standard, particularly with utility members who have expertise in practical CVR deployments. The plan is to develop, review, and publish the standard by mid-2022.
This is a pivotal time to ensure that the grid can be operated more efficiently than ever by intelligently deploying CVR and VVO by accurately estimating the benefits. Providing an industry standard that can further serve as a guideline and roadmap for electric utilities on how to best approach this challenging effort is of utmost importance. It is only achievable through contributions of volunteer subject matter experts who join the Taskforce and dedicate time and expertise to brainstorm and develop solutions that effectively address existing challenges.
The Taskforce welcomes volunteers from throughout the utility industry who have expertise in the area of CVR M&V. Interested parties may contact the committee (CVR M&V Taskforce, Contact Chair: Shakawat (Shakil) Hossan, [email protected]) for more information.
References
[1] ANSI, "ANSI Standard C84.1-2016 Electric Power Systems and Equipment Voltage Ratings (60 Hz)," 2016
[2] Z. Wang and J. Wang, "Review on Implementation and Assessment of Conservation Voltage Reduction," in IEEE Transactions on Power Systems, Vol. 29, No. 3, pp. 1306-1315, May 2014
[3] Z.S. Hosseini et al., "Conservation Voltage Reduction and Volt-VAR Optimization: Measurement and Verification Benchmarking," in IEEE Access, Vol. 8, pp. 50755-50770, 2020
