PV DEGRADATION
DEGRADATION
Degradation is discussed in the 3 International Electrotechnical Commission (IEC) 61724 Photovoltaic System Performance standards.
- IEC 61724 – 1 Monitoring
- IEC 61724 – 2 Capacity evaluation method
- IEC 61724 – 3 Energy evaluation method
Referring to the IEC 61724 standard above, it can be concluded that internationally recognized standards acknowledge the existence of degradation or a decrease in performance in PV modules.
IEC 61724 – 1 MONITORING
Establishing three classification categories for PV monitoring systems with different levels of accuracy (Class A, B, C). The choice of classification depends on the system size and user objectives. Class A or B is suitable for large PV systems, while Class B or C is more appropriate for small systems. Users can refer to the classifications by letter code (A, B, C) or by name (high, medium, basic accuracy). Specific requirements apply to each classification, and this document provides flexibility for standard users to determine the classification that suits their application.
According to IEC 61724-1 Chapter 4, measuring degradation becomes a crucial part that must be monitored and is one of the requirements to meet the Class A or High Accuracy classification.
IEC 61724 – 2 CAPACITY EVALUATION METHOD
Beberapa modul PV menunjukkan perubahan kinerja yang dapat diukur dalam hitungan jam atau hari setelah dipasang di lapangan ; tetapi tidak semuanya. The test duration should be negotiated between the parties using the manufacturer’s guidelines for the required number of days of exposure or radiation exposure needed for the power plant to achieve the targeted performance. This should include detailed installation and interconnection dates. Any metastability (variability in module efficiency depending on previous operating conditions) and degradation assumptions (including those with short and long time constants) should be agreed upon by all parties and documented as part of the target description.
Based on IEC 61724-2 bab 4 required performed measurement capacity PV module in periodic and scheduled for knowing performance or performance from PV Module. result measurement this will in comparison to with warranty performance from brand PV Module that used.
IEC 61724 – 3 Energy Evaluation Method
Some PV modules exhibit performance changes that can be measured within hours or days after installation in the field; others do not. The test initiation should be negotiated between stakeholders using manufacturer guidelines for the number of days or radiation exposure required for the power plant to achieve modeled performance, along with the actual installation and interconnection dates. Assumptions regarding degradation must be agreed upon by all stakeholders and documented as part of the model description. It is recommended that the test takes place over 365 days, and the actual duration should be agreed upon in advance. If the test is not conducted for a full year, seasonal variations may cause performance deviations from what would be obtained over a full year. The performance metric, energy performance index when operating, is reported only for the time when the inverter and other components are operating. The expected energy when the inverter or other components are not operating is measured in the energy unavailability metric. The energy unavailability metric can be further divided into situations with internal and external causes, in accordance with stakeholder agreements. (This is similar to the PCM present in the PPA.)
Based on IEC 61724-3 chapter 4, periodic measurements of the PV module output need to be conducted, which serves as a reference for the Predictive Capacity Matrix (PCM) present in the Power Purchase Agreement (PPA).
DEGRADATION
There are several types of degradation that can affect PV modules.
- Degradation due to Potential Induced Degradation (PID): This type of degradation is often caused by voltage potential differences between the grounding system and the conductive parts of the module, resulting in leakage currents that can damage the module over time.
- Degradation due to Light Induced Degradation (LID): Ultraviolet (UV) light, in particular, can damage the cover materials and cause color changes in PV cells, reducing efficiency. This is also known as photodegradation.
- Degradation due to environmental factors: The primary environmental factors causing degradation in PV modules include temperature, sunlight, rain, wind, humidity, mechanical pressure, and the accumulation of dirt/sand, which can lead to physical damage to module components, resulting in degradation. These factors often interact and combine to reduce the efficiency and lifespan of solar panels during their operational life. Proper closure, installation, and maintenance of modules can help reduce some of these environmental degradation effects (Atia et al., 2023).
1. Potential-Induced Degradation (PID)
Voltage in solar cells has both negative and positive potential. Negative potential triggers PID in solar cells. Typically, photons allow electrons to flow to the cell’s connectors, generating current. However, negative potential attracts positive ions within the cell, such as sodium ions, which stimulate surface polarization and shunting. This movement usually occurs from the glass plate through the protective layer and anti-reflective coating to the cell. The electrons then cease to flow, leading to a disruption in junction function, resulting in a decrease in panel power capacity.
After several weeks or months, PID occurs across the negative side of the string. The most negative panel can lose 30-80% of its yield. PID is contagious, more cells are affected over time, and those cells turn black. The speed of PID depends on the system voltage, humidity level, and cell temperature. PID can be reversible or irreversible. Therefore, it has adverse effects on all levels of PV system installations – financing, operation, and economics. Solar investors must address PID effects in the early stages to ensure the PV system operates efficiently throughout its lifecycle (Novergy, 2020).
The above image shows a comparison of the I-V curve between a PV module affected by PID and one not affected by PID (Turmino, 2020).
𝑃𝑀𝑃𝑃,u = Daya Maximum Power Point Unaffected
It represents the maximum output power produced by a PV module when not subjected to voltage stress (Not affected by PID).
𝑃𝑀𝑃𝑃,𝑎 = Daya Maximum Power Point Affected
It represents the maximum output power produced by a PV module when subjected to voltage stress (Affected by PID).
2. LIGHT-INDUCED DEGRADATION (LID)
Light exposure causing damage to PV modules. In this type, ultraviolet (UV) light, in particular, can damage the cover material and cause a change in the color of the PV cell, reducing efficiency. This is also known as photodegradation (Atia et. al, 2023).
UV light can break down the module’s cover material, causing a change in color in PV cells, which impacts efficiency. This process is known as photodegradation. Prolonged exposure to sunlight and UV radiation can damage the structure and performance of solar cells, reducing the power output of the module. Additional protection such as UV-resistant cover materials and the selection of materials resistant to radiation can help mitigate these destructive effects, enhancing the durability and performance of PV modules against Light-Induced Degradation (Rodríguez, 2021).
The image above shows a comparison of the open-circuit voltage (Voc) produced by PV modules over the duration of module usage. The graph indicates that there is degradation due to Light-Induced Degradation (LID), as the longer the PV module is used, the open-circuit voltage (Voc) produced by the PV module will decrease (Sporleder et al., 2017).
3. DEGRADATION DUE TO ENVIRONMENTAL FACTORS
The primary environmental factors causing degradation in PV modules include temperature, sunlight exposure, rain, wind, humidity, mechanical pressure, and the accumulation of dirt/sand. These factors can lead to physical damage to module components, resulting in degradation. These factors often interact and combine to reduce the efficiency and lifespan of solar panels during their operational life. (Atia et. al, 2023).
When operating in hot and humid climates, PV modules undergo changes in moisture content, which overall correlates with module performance degradation. If moisture starts to penetrate into the polymer and reaches the solar cells, it can weaken the adhesive bonds at the interface, causing delamination and an increase in the number of entry paths, loss of passivation, and corrosion at solder joints (Park et.al, 2013).
The above image shows a comparison of voltage and current from a PV module without dust to a PV module with dust on it. Efek debu mengakibatkan kinerja modul PV mengalami penurunan karena arus hubung singkat (Isc) mengalami penurunan dari nilai minimum yang ditetapkan (Akter et.al, 2020).
Author : Natasyah Adelina & Dwi Kurniawan