The Future of Solar Asset Management: Embracing the Energy Performance Index

The Role of Performance Metrics in Monitoring and Optimization

In the competitive solar energy landscape, Asset Management and O&M professionals constantly strive 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. Performance metrics play a crucial role in identifying areas for improvement, ensuring optimal operation, and minimizing downtime. These metrics not only maintain the health of solar plants but also contribute to maximizing return on investment.

Performance Ratio (PR) vs. Energy Performance Index (EPI): Advantages and Disadvantages

While there are three prime performance metrics in the solar industry, we will be leaving Availability for a separate discussion and for today narrow down only on: Performance Ratio (PR) and Energy Performance Index (EPI). EPI is not used quite as widely as PR and both these KPIs possess distinct advantages and disadvantages that can impact their effectiveness as performance indicators. In this article, we will explore the pros and cons of both PR and EPI and discuss why embracing the Energy Performance Index could be the future of solar asset management.

Performance Ratio (PR) Advantages:

Simple calculation: PR’s simplicity is one of the main reasons for its widespread acceptance in the solar industry. PR calculations require minimal data inputs, making it accessible for professionals at all levels of expertise.  

Comprehensive efficiency measurement: PR accounts for multiple factors that can affect a solar PV system’s performance, providing a comprehensive measure of overall efficiency. This makes it a valuable tool for evaluating the effectiveness of solar installations.  

Industry-wide recognition: PR is a well-established metric and is widely recognized by industry professionals. This widespread use allows for easier communication and benchmarking of performance results within the solar community.

Performance Ratio (PR) Disadvantages:

Weather dependency: PR is highly dependent on weather conditions, introducing unnecessary risk in contractual acceptance testing. System output can vary significantly with temperature, irradiance, and spectrum. 


Design feature exclusion: PR calculations do not consider design features such as tilt of PV modules, mounting height, row-to-row shading, and diodes, which means that PR may not accurately reflect the impact of these design elements on the system’s 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 analysis: PR is better suited for analyzing the entire PV site rather than individual components, such as inverters or strings. This limitation can hinder its usefulness for diagnosing specific performance issues within a solar power plant. 


Curtailment and clipping concerns: PR for overrated plants can be misleading due to higher DC power than inverter AC power, resulting in limited output during sunny periods. This can cause derating, leading to lower PR values despite no technical issues with the plant. In such cases, lower PR values are a result of design decisions rather than technical problems. 


Reliance on historical average data and declarative approach: PR relies on historical average data and a declarative approach, which can be manipulated in systems like PVSyst. This reliance can lead to inaccuracies in the PR calculations. 


Inconsistency in 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.

Energy Performance Index (EPI) Advantages:

Climate and weather independence: EPI is not affected by meteorological conditions, making it a more stable and reliable metric for assessing solar plant performance. This independence allows for more accurate performance evaluations and reduces the risks associated with contractual acceptance testing. 


Component comparison capability: Unlike PR, EPI enables the analysis of individual components within a solar installation, such as inverters, strings, and modules. This granular approach helps pinpoint specific areas of concern, making it easier for PV Asset Management and O&M experts to address performance issues. For example, EPI can be used to compare the performance of different inverters within a solar farm, identify underperforming strings due to shading or other issues, or assess the efficiency of various module technologies in different operating conditions. It is important to understand that on one day, an inverter producing 10kW may have an EPI level of 100%, while another producing 200kW may have 60%. The amount of kW does not define the level of performance. 


Real-time monitoring: EPI provides real-time information on any potential drops in performance, enabling quick action to remedy problems and minimize downtime. This real-time monitoring capability is vital for optimizing system performance and ensuring maximum energy production. 


Facilitates comparison between diverse sites: EPI allows for the comparison of solar farms, regardless of their geographic location. This is due to the physical model used to calculate Expected Yield, which takes into account nearly all circumstances affecting photovoltaic farms. Consequently, EPI makes it easier to evaluate the performance of solar assets across different regions and climates. 


Quick identification of poorly performing components: EPI’s ability to analyze individual components helps identify underperforming elements within the solar installation. This allows for prompt intervention and problem resolution, allowing to minimize time from defect detection to resolution, therefore limiting the potential power generation losses, improving overall system performance and efficiency.

Energy Performance Index (EPI) Disadvantages:

Complexity of calculations: EPI calculations can be complex and require a substantial amount of data, which may be difficult to obtain or inaccurate. This complexity can pose challenges for some industry professionals, particularly those with limited experience or resources or using 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 EPI metric, limiting its usefulness 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 the ability to conduct automated anomaly detection. By leveraging the detailed insights provided by EPI as a base to observe potential anomalies, Solar Spy utilizes in-house developed AI and machine learning (ML) algorithms to identify underperformance issues and diagnose performance gaps in real-time, effectively streamlining the maintenance process. For example, the system can detect issues on string level such as shading due to dust or debris accumulation, and inverter malfunctions, among others. 


These AI and ML algorithms are continuously improved and updated, enabling Solar Spy’s platform to provide even more accurate and timely detection of potential issues. Once an anomaly is detected, the system analyzes the time series data to determine the root cause of the problem. As a result, PV Asset Management and O&M professionals can address problems before they escalate, preventing more significant losses in energy production and revenue.  


This advanced capability is complemented by Solar Spy’s dedicated Maintenance Management platform and Mobile App, which help simplify operations and provide an accessible entry point for newcomers to the solar industry. The Maintenance Management platform offers a user-friendly interface for tracking and scheduling maintenance tasks, while the Mobile App enables 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 speeds up the time from anomaly detection to resolution, minimizing downtime and ensuring optimal performance of solar assets. For instance, 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 helps reduce the time spent on repairs, ultimately increasing the overall efficiency and productivity of the solar power plant.


The solar industry’s rapid growth and increasing complexity necessitate a robust and comprehensive metric for PV asset management. EPI stands out as the superior choice in this regard, offering a more accurate and reliable approach than the traditional Performance Ratio (PR). EPI’s independence from weather and climate conditions, as well as its ability to analyze individual components within a solar installation, sets it apart as a superior metric. Furthermore, EPI’s real-time monitoring capabilities enable swift action to remedy 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. By offering accurate EPI calculations and advanced PV asset health and maintenance management solutions, Solar Spy empowers its clients to make data-driven decisions that maximize system efficiency, reduce downtime, and improve return on investment.  


The future of solar asset management relies on embracing innovative solutions like EPI and advanced technologies offered by companies like Solar Spy. Don’t miss 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 solutions. Take the first step towards optimizing your solar assets by scheduling a personalized demo below.