The future of solar Asset Management: Embracing the Energy Performance Index

In the competitive solar energy landscape, Asset Management and O&M professionals are constantly striving to optimize the performance of solar power plants. To achieve this, they rely on performance metrics that accurately evaluate and monitor the efficiency and effectiveness of solar installations. These metrics are essential for identifying areas for improvement, ensuring optimal operation and minimizing downtime. Ultimately, they not only safeguard the health of solar plants but also help maximize return on investment. 

Performance Ratio vs. Energy Performance Index: Weighing the Pros and Cons

While there are three primary performance metrics in the solar industry, we will leave Availability for a separate discussion and focus today on Performance Ratio (PR) and Energy Performance Index (EPI). Although EPI is not as widely used as PR, both KPIs have distinct advantages and disadvantages that can influence their effectiveness as performance indicators. In this article, we will examine the pros and cons of each and discuss why embracing the Energy Performance Index could shape the future of solar asset management. 

Advantages of Performance Ratio (PR)

Below are the key strengths that have made PR a widely adopted metric in the solar industry.

• Simple calculation: PR’s simplicity is one of the main reasons for its widespread use in the solar industry. It requires minimal data inputs, making it accessible to professionals at all levels of expertise.
• Comprehensive efficiency measurement: PR considers multiple factors that influence a solar PV system’s performance, offering a holistic measure of overall efficiency. This makes it a valuable tool for evaluating the effectiveness of solar installations.
• Industry-wide recognition: PR is a long-established metric, widely recognized by industry professionals. Its broad adoption enables easier communication and benchmarking of performance results across the solar community.

Disadvantages of Performance Ratio (PR)

Despite its popularity PR has several limitations that can affect its accuracy and applicability.

• Weather dependency: PR is highly influenced by weather conditions, introducing risk in contractual acceptance testing. System output can vary significantly with temperature, irradiance, and spectrum.
• Design feature exclusion: PR does not account for design factors such as PV module tilt, mounting height, row-to-row shading, or diode configuration. As a result, it may fail to reflect the impact of these elements on system performance.
• Limited design comparison: Comparing different solar power plants, such as bifacial and single-sided module sites, is challenging using PR due to its limitations in accounting for design differences. The introduction of new bifacial modules metrics in the market has shown that most of the analytics are only relevant to mono-facial modules, and their use with bifacial modules can provide misleading results, frequently resulting in over 100% PR.
• Annual analysis focus: PR is primarily used for annual analysis, as seasonal variations can cause high variability in the metric, especially during winter months when radiation values are lower.
• Inadequate for component-level analysis: PR is better suited for evaluating the entire PV site rather than individual components (e.g., inverters or strings). This limits its usefulness for diagnosing specific performance issues.
• Curtailment and clipping concerns: In overrated plants, high DC power compared to inverter AC capacity can cap output on sunny days. This derating lowers PR despite no technical faults, making it a design-driven issue rather than a performance problem.
• Reliance on historical averages and declarative methods: PR often depends on historical average data and simulation-based approaches (e.g., PVSyst), which can be manipulated, leading to inaccuracies.
• Inconsistent reference conditions: The market has started to recognize that using Standard Test Conditions (STC) is irrelevant and has begun adopting Normal Operating Cell Temperature (NOCT) instead. However, this change brings possible confusion, as some industry professionals still use STC for PR calculations, while others have switched to using NOCT. This inconsistency makes it difficult to compare PR values across different solar installations and can lead to further inaccuracies.

Advantages of Energy Performance Index (EPI)

The following points highlight why EPI is gaining recognition as a preferred performance metric.

• Climate and weather independence: EPI is unaffected by meteorological conditions, making it a stable and reliable metric for assessing solar plant performance. This independence enables more accurate evaluations and reduces the risks associated with contractual acceptance testing.
• Component-level comparison: Unlike PR, EPI supports the analysis of individual components such as inverters, strings, and modules. This granular view helps pinpoint specific issues for Asset Management and O&M teams. For example, EPI can compare the performance of different inverters within the same farm, detect underperforming strings caused by shading or other factors, or assess the efficiency of various module technologies. It is important to note that output in kilowatts alone does not define performance. An inverter producing 10 kW may have an EPI of 100%, while another producing 200 kW could have 60%.
• Real-time monitoring: EPI provides immediate insights into potential drops in performance, enabling rapid response to issues. This capability helps minimize downtime and optimize overall energy production.
• Cross-site comparability: Thanks to the physical model used to calculate Expected Yield, which factors in nearly all circumstances affecting PV farms, EPI allows for fair comparisons between sites regardless of location or climate.
• Faster fault detection and resolution: EPI’s detailed analysis of individual components enables quick identification of underperforming elements. This accelerates intervention, reduces the time from defect detection to resolution, limits potential power generation losses, and improves overall efficiency.

Disadvantages of Energy Performance Index (EPI)

While EPI offers clear benefits it also comes with certain challenges and considerations.

• Complexity of calculations: EPI calculations can be complex and require a substantial amount of data, which may be difficult to obtain or may be inaccurate. This complexity can pose challenges for some industry professionals, particularly those with limited experience, limited resources or outdated software solutions.
• Data dependency and availability: EPI calculations rely on comprehensive data about the solar system, which may not always be readily available. Inaccurate or incomplete data can compromise the accuracy and reliability of the metric, reducing its value as a performance indicator.

EPI and Automated Defect Detection

One of the key benefits of using EPI with Solar Spy’s PV site health monitoring platform is its ability to conduct automated anomaly detection. By using the detailed insights provided by EPI as a foundation for observing potential anomalies, Solar Spy applies in-house developed AI and machine learning (ML) algorithms to identify underperformance issues and diagnose performance gaps in real time, streamlining the maintenance process. For example, the system can detect issues at the string level, such as shading caused by dust or debris accumulation as well as inverter malfunctions and other faults.

These AI and ML algorithms are continuously improved and updated, enabling Solar Spy’s platform to deliver increasingly accurate and timely detection of potential issues. Once an anomaly is detected, the system analyzes time-series data to identify the root cause of the problem. This allows PV Asset Management and O&M professionals to address issues before they escalate, preventing significant losses in energy production and revenue.

This advanced capability is complemented by Solar Spy’s dedicated Maintenance Management platform and mobile app, which simplify operations and provide an accessible entry point for newcomers to the solar industry. The Maintenance Management platform features a user-friendly interface for tracking and scheduling maintenance tasks, while the mobile app allows technicians to access real-time information about the solar site, receive notifications of detected issues, and update maintenance records directly from the field.

The seamless integration of these technologies significantly shortens the time from anomaly detection to resolution, minimizing downtime and ensuring optimal performance of solar assets. For example, a technician can receive an alert about a detected issue, such as a faulty inverter, and quickly diagnose and resolve the problem on-site using the mobile app. This streamlined process reduces repair time and ultimately increases the overall efficiency and productivity of the solar power plant.

Conclusion

The rapid growth and increasing complexity of the solar industry demands a robust and comprehensive metric for PV asset management. EPI stands out as the superior choice, offering a more accurate and reliable approach than the traditional Performance Ratio (PR). Its independence from weather and climate conditions, along with the ability to analyze individual components within a solar installation, sets it apart. In addition, EPI’s real-time monitoring capabilities enable swift action to address problems, minimizing downtime and ensuring maximum energy production.

Solar Spy is committed to helping PV Asset Management and O&M professionals stay ahead in an increasingly competitive solar industry. Through accurate EPI calculations and advanced PV asset health and maintenance management solutions, Solar Spy empowers clients to make data-driven decisions that maximize system efficiency, reduce downtime and improve return on investment.

The future of solar asset management depends on adopting innovative solutions such as EPI and advanced technologies from companies like Solar Spy. Take the opportunity to stay ahead in the competitive solar landscape and ensure the long-term success of your solar power plants. Join the growing community of PV Asset Management and O&M professionals who trust Solar Spy for accurate EPI calculations, automated defect detection and streamlined maintenance management. Take the first step toward optimizing your solar assets by scheduling a personalized overview session with us. Comment below to learn more.

This article by Michał Frys was originally published on Solar Spy’s website and has been adapted for LinkedIn.