PV System Performance Monitoring
Hafiz Shahzad Ahmad Mukhtar
Power Plant Electrical Maintenance Specialist I Site Manager I Plant General Manager I Electrical Section Head
PV system Performance Monitoring
Monitoring the performance of photovoltaic (PV) systems using various performance metrics and monitoring techniques is of utmost importance. These metrics, such as performance ratio, performance index, energy yield, specific energy yield, PV system efficiency, and electrical and non-electrical PV monitoring techniques, play a vital role in optimizing energy generation, detecting faults, ensuring peak efficiency, and maximizing return on investment. They allow for accurate assessment of the system's overall efficiency, identification of potential issues or degradation, comparison with expected energy production, and evaluation of the system's ability to convert solar irradiance into electrical energy. By implementing a comprehensive monitoring system that encompasses these metrics and techniques, PV system owners can proactively address any performance deviations, enhance system reliability, and maximize energy production and financial benefits.
Following is the table of content of this article:
1. Electrical and Non Electrical Monitoring Techniques:??????????
A- Electrical Monitoring Techniques:???????
a) Current-Voltage (I-V) Curve Measurement:???
b) Electroluminescence (EL) Imaging:??????
B- Non-Electrical Testing Techniques:?????
a) Visual Inspection:
b) Thermal Imaging:
c) Ultraviolet (UV) Fluorescence Imaging:???????????
d) Electromagnetic Field (EMF) Measurement:?
2. Sophisticated PV Performance Metrics
a. Performance Ratio (PR):?
b. Energy Yield:????????
c. Performance Index (PI):?
d. Specific Energy Yield (SEY):???????
3. Issues Highlighted by Each Metric:??????
4. Comprehensive Performance Analysis:???????????
a. Benchmarking:????
b. Trend Analysis:????
c. Comparison:?????????
d. Environmental Factors:?
e. System-Level Analysis:???
f. Historical Data:????
1. Electrical and Non Electrical Monitoring Techniques:
Here's a detailed explanation of the electrical and non-electrical testing techniques to monitor the performance of PV modules and systems, including the procedure, evaluation criteria, standard references, result interpretation, and recommended tools:
A- Electrical Monitoring Techniques:
a) Current-Voltage (I-V) Curve Measurement:
Procedure:
1. Set up the PV module in a controlled environment or using a solar simulator.
2. Sweep the voltage across the module while measuring the corresponding current at each point.
3. Plot the I-V curve to visualize the module's performance characteristics.
Evaluation Criteria:
- Shape of the I-V curve: Smooth, well-defined curve without significant irregularities.
- Maximum power point (MPP) voltage and current: Maximum power output of the module.
- Open-circuit voltage (Voc): Voltage at zero current.
- Short-circuit current (Isc): Current at zero voltage.
- Fill factor (FF): Ratio of the maximum power to the product of Voc and Isc.
- Overall performance: Comparing measured values with expected or standard values.
Standard Reference:
IEC 61853 provides guidelines for I-V curve measurement.
Result Interpretation:
- Deviations in curve shape or irregularities may indicate shading, soiling, or cell degradation.
- Significant deviations in MPP, Voc, Isc, or FF may indicate performance issues or module degradation.
Recommended Tools:
Solartron, Keysight Technologies, or Keithley Instruments offer I-V curve tracers and source meters suitable for PV module testing.
b) Electroluminescence (EL) Imaging:
Procedure:
1. Prepare the PV module by ensuring it is free from direct sunlight or external light sources.
2. Activate the electroluminescent effect by applying a low-level electrical excitation to the module.
3. Capture the electroluminescent image using an EL imaging camera.
Evaluation Criteria:
- Cell uniformity: Uniform luminescent response across the module's cells.
- Dark spots: Absence of dark areas indicating cell defects or damage.
- Color deviations: Uniformity in cell color indicating consistent performance.
- Presence of hot spots: No localized areas of intense luminescence indicating potential issues.
Standard Reference:
No specific standard reference exists for EL imaging, but industry guidelines and best practices should be followed.
Result Interpretation:
- Dark spots, discoloration, or hot spots may indicate cell damage or performance degradation.
- Non-uniformities or irregularities in the EL image may require further investigation.
Recommended Tools:
Photovoltaic Diagnostics and InfraTec offer EL imaging cameras suitable for PV module inspection.
B- Non-Electrical Testing Techniques:
a) Visual Inspection:
Procedure:
1. Visually inspect the PV module and system components.
2. Check for any visible signs of damage, degradation, or anomalies.
3. Document observations through photographs or notes.
Evaluation Criteria:
- Module surface condition: No cracks, scratches, or physical damage.
- Module frame integrity: No bending, warping, or corrosion.
- Connections: Tight and secure electrical connections.
- Module soiling: Minimal accumulation of dirt or debris.
- Physical damages: Absence of shattered glass or significant physical impacts.
Standard Reference:
No specific standard reference exists for visual inspection, but industry best practices should be followed.
Result Interpretation:
- Identify visible issues, such as cracks, broken glass, loose connections, or physical damages.
- Soiling or debris accumulation may impact performance and require cleaning or maintenance.
Recommended Tools:
No specific tools are required for visual inspection. However, using a flashlight, magnifying glass, and a camera or smartphone for documentation can be helpful.
b) Thermal Imaging:
Procedure:
1. Set up the thermal imaging camera in a controlled environment.
2. Capture thermal images of the PV module or system.
3. Analyze the temperature distribution and anomalies in the images.
Evaluation Criteria:
- Temperature differentials: Uniform temperature distribution across the module.
- Presence of hot spots: No localized areas of high temperature indicating potential issues.
Standard Reference:
The IEC 60904-8 standard provides guidelines for thermal imaging of PV modules.
Result Interpretation:
- Hot spots or non-uniform temperature distributions may indicate cell or module-level issues such as bypass diode failure, cell degradation, or shading.
Recommended Tools:
FLIR Systems, Testo, or FLUKE offer thermal imaging cameras suitable for PV module inspection.
c) Ultraviolet (UV) Fluorescence Imaging:
Procedure:
1. Set up the UV light source and UV fluorescence camera.
2. Illuminate the PV module's surface with UV light.
3. Capture the UV fluorescence image using the camera.
Evaluation Criteria:
- Presence of fluorescence patterns: No irregular fluorescence patterns.
- Dark areas: No localized areas of reduced fluorescence indicating defects or damage.
- Abnormal patterns: Consistent fluorescence patterns across the module.
Standard Reference:
No specific standard reference exists for UV fluorescence imaging, but it is considered a useful tool for quality assessment.
Result Interpretation:
- Visible fluorescence patterns, dark areas, or irregularities may indicate potential defects, cracks, or contamination affecting module performance.
Recommended Tools:
Konica Minolta or Hamamatsu offer UV light sources, UV filters or goggles, and UV fluorescence cameras suitable for UV fluorescence imaging.
d) Electromagnetic Field (EMF) Measurement:
Procedure:
1. Set up the EMF meter or field strength meter.
2. Measure the electromagnetic fields around the PV system components.
3. Record the measurements at various points.
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Evaluation Criteria:
- Compliance with relevant EMF exposure limits specified by local regulations or guidelines.
Standard Reference:
Local regulations and guidelines specify the exposure limits for EMF.
Result Interpretation:
- Compare the measured EMF levels with the specified limits. Excessive EMF levels may indicate wiring or grounding issues affecting system performance or safety.
Recommended Tools:
Narda Safety Test Solutions, Gigahertz-Optik, or Extech Instruments offer EMF meters and field strength meters suitable for PV system EMF measurements.
It's important to note that specific brands and models of these tools may vary based on availability and user preference. It is recommended to select tools that meet the necessary accuracy, sensitivity, and specifications required for the specific testing technique.
Additionally, for accurate and reliable results, proper calibration, adherence to safety procedures, and compliance with relevant standards and guidelines are essential. Always consult the manufacturer's instructions, industry best practices, and qualified professionals when conducting performance testing of PV modules and systems.
2. Sophisticated PV Performance Metrics
Here are the explanations of the sophisticated performance metrics used to assess the performance of PV systems, including the calculation procedure, examples, evaluation criteria, standard references, result interpretation, and recommended tools:
a. Performance Ratio (PR):
The Performance Ratio (PR) is a widely used metric to evaluate the performance of a PV system by comparing the actual energy output to the expected energy output under standard conditions.
Calculation Procedure:
The performance ratio?is a measure of the quality of a PV plant that is independent of location?and it therefore often described as a a quality factor. The performance ratio (PR) is stated as percent and describes the relationship between the actual and theoretical energy outputs of the PV plant.
“Performance Ratio (PR)” is defined as below:
Performance Ratio (PR) of a plant for a period of time?═?Energy generated (kWh /) / Irradiance (kWh/m2) x Active area of PV module (m2) x PV module efficiency
Alternatively, the following formula may be used for calculation of PR?
PR = ((Energy generated / (installed plant capacity in KW *solar insolation in KWH/m2/ day))
Let's break down the components of the formula and provide an example to illustrate its usage:
Example:
Let's consider a PV system that generated 10,000 kWh of energy over a specific period. The irradiance during that period was 1,000 kWh/m2, and the active area of the PV module was 10 m2. The PV module efficiency is assumed to be 15%.
PR = (10,000 kWh / (1,000 kWh/m2 x 10 m2 x 0.15))
= (10,000 kWh / 150 kWh)
= 66.67
In this example, the calculated PR value is 66.67.
The Performance Ratio (PR) is a widely used metric to evaluate the performance of a PV system. It compares the actual energy output of the system to the expected energy output under standard conditions.
Evaluation Criteria:
- The PR should ideally be close to 100% to indicate optimal performance. A higher PR suggests better performance, while a lower PR may indicate issues such as shading, soiling, or module degradation. To assess the module's performance comprehensively, it's essential to compare the PR with reference values or industry standards.
- Deviations from 100% may occur due to losses from shading, soiling, module degradation, wiring issues, or other system inefficiencies.
Standard Reference:
IEC 61724 provides guidelines for calculating the PR of PV systems.
Result Interpretation:
- A higher PR indicates better performance and efficiency.
- Lower PR values suggest underperformance and the need for investigation into the causes of energy losses.
Recommended Tools:
Power meters, energy meters, data loggers, and monitoring software can be used for measuring the energy yield and peak power of the PV system. Brands like Efergy, Schneider Electric, and SolarEdge offer suitable tools for energy monitoring.
b. Energy Yield:
Energy Yield represents the actual energy generated by a PV system over a specific period, typically a year, and is measured in kilowatt-hours (kWh).
Calculation Procedure:
Energy Yield = Total Energy Output / Installed Capacity
The Energy Yield represents the actual energy generated by a PV system over a specific period (usually a year) and is measured in kilowatt-hours (kWh). It is calculated by dividing the total energy output (in kWh) by the installed capacity of the PV system (in kilowatts).
Example:
Consider a PV system with an installed capacity of 1 MWp and an annual energy output of 300 MWh.
Energy Yield = 300 MWh / 1 MWp = 300 kWh/kWp
Evaluation Criteria:
- Energy Yield should be maximized to ensure optimal performance. This metric helps evaluate the productivity of the PV module. Higher energy yield values indicate greater energy production relative to the module's rated power. It can be used to compare the performance of different PV modules or to assess the impact of environmental factors on energy generation.
- Deviations from expected values may indicate losses from shading, soiling, module degradation, or system inefficiencies.
Standard Reference:
No specific standard reference exists for Energy Yield, but it is commonly used in PV system analysis.
Result Interpretation:
- Higher Energy Yield values indicate better performance and higher energy generation.
- Lower Energy Yield values suggest underperformance or energy losses.
Recommended Tools:
Power meters, energy meters, and data loggers are used for measuring the total energy output. Brands like Efergy, Schneider Electric, and SolarEdge offer suitable tools for energy monitoring.
c. Performance Index (PI):
The Performance Index (PI) is a metric that compares the actual performance of a PV system to its reference performance under specific conditions.
Calculation Procedure:
PI = (Energy Yield / (Reference Yield x Installed Capacity)) * 100
To calculate PI, you divide the Energy Yield (the actual energy generated by the system) by the product of the Reference Yield (the expected energy output under standard conditions) and the Installed Capacity of the system. The result is then multiplied by 100 to express it as a percentage.
The Performance Index (PI) is a metric that compares the actual performance of a PV system to its reference performance under specific conditions. It provides a relative measure of the system's performance efficiency.
Example:
Assume a PV system with an installed capacity of 1 MWp, an Energy Yield of 300 MWh, and a Reference Yield of 350 MWh.
PI = (300 MWh / (350 MWh x 1 MWp)) * 100 = 85.7%
Evaluation Criteria:
- A PI of 100% indicates that the PV system is performing at its expected reference performance.This metric provides insight into how well the module performs compared to its expected performance under ideal conditions. A PI close to 100% suggests the module is operating near its rated performance, while a lower PI may indicate performance degradation or non-optimal operating conditions.
- Deviations from 100% may indicate underperformance or overperformance compared to the reference values.
Standard Reference:
No specific standard reference exists for PI, but it is widely used in PV system performance assessment.
Result Interpretation:
- A higher PI value indicates better performance relative to the reference performance.
- Lower PI values suggest underperformance or inefficiencies in the PV system.
Recommended Tools:
Power meters, energy meters, and data loggers are used for measuring the energy yield. Monitoring software and modeling tools can assist in calculating the reference yield. Brands like Efergy, Schneider Electric, and SolarEdge offer suitable tools for energy monitoring.
d. Specific Energy Yield (SEY):
Specific Energy Yield (SEY) measures the energy generated by a PV system per unit of its peak power, providing a normalized metric for performance comparison.
Calculation Procedure:
SEY = Energy Yield / Peak Power
To calculate SEY, you divide the Energy Yield (the actual energy generated by the system) by the Peak Power (the maximum power output of the system under standard test conditions).
The Specific Energy Yield (SEY) is a performance metric that measures the energy generated by a PV system per unit of its peak power. It provides a normalized metric for comparing the energy generation efficiency of different PV systems.
Example:
For a PV system with an Energy Yield of 300 MWh and a peak power of 100 kWp:
SEY = 300 MWh / 100 kWp = 3,000 kWh/kWp
Evaluation Criteria:
- Higher SEY values indicate better energy generation efficiency per unit of peak power.This metric helps assess the energy production efficiency based on the module's physical size. It allows for comparisons between different PV modules or systems with varying areas. Higher SEY values indicate higher energy production efficiency for a given module area.
- Deviations from expected values may indicate losses or inefficiencies in the PV system.
Standard Reference:
No specific standard reference exists for SEY, but it is widely used in PV system performance analysis.
Result Interpretation:
- Higher SEY values indicate better performance and efficiency.
- Lower SEY values suggest underperformance or energy losses.
Recommended Tools:
Power meters, energy meters, and data loggers are used for measuring the energy yield and peak power. Brands like Efergy, Schneider Electric, and SolarEdge offer suitable tools for energy monitoring.
3. Issues Highlighted by Each Metric:
- Performance Ratio (PR): PR highlights overall system efficiency, including losses from shading, soiling, degradation, and system inefficiencies.
- Energy Yield: Energy Yield identifies the actual energy generated by the PV system and highlights losses from various factors.
- Performance Index (PI): PI compares the actual performance to the reference performance and indicates relative performance deviations.
- Specific Energy Yield (SEY): SEY provides a normalized metric to compare energy generation efficiency per unit of peak power.
Please note that specific brands and models of tools may vary based on availability and user preference. It is recommended to select tools that meet the necessary accuracy, sensitivity, and specifications required for the specific metric.
Additionally, adherence to safety procedures, compliance with relevant standards and guidelines, and proper calibration of measuring equipment are essential for accurate and reliable performance assessment of PV systems.
4. Comprehensive Performance Analysis:
To perform a comprehensive performance analysis based on these values, consider the following steps:
a. Benchmarking:
Compare the obtained performance metrics with reference values or industry standards to evaluate the module's performance relative to similar modules or systems.
b. Trend Analysis:
Track the performance metrics over time to identify any deviations or trends. This helps identify potential degradation, system issues, or performance improvements.
c. Comparison:
Compare the performance metrics with other PV modules or systems in the same installation to identify any underperforming units that may require maintenance or replacement.
d. Environmental Factors:
Consider the impact of environmental factors such as temperature, shading, soiling, and irradiance levels on the performance metrics. Assess any potential issues or optimizations related to these factors.
e. System-Level Analysis:
If multiple PV modules are connected in strings or arrays, analyze the performance metrics at the system level. Evaluate the overall energy output, efficiency, and possible losses in the system.
f. Historical Data:
Maintain a historical record of performance metrics to track long-term performance trends, identify degradation rates, and make informed decisions regarding maintenance, cleaning, or module replacement.
By performing a comprehensive analysis using these steps and considering the various performance metrics, you can gain insights into the performance of the PV module and make informed decisions to optimize its efficiency, identify potential issues, and ensure optimal energy production.