Content:
- What is Potential Induced Degradation (PID)Effect in solar panels?
- Why does Potential Induced Degradation(PID) Effect occur?
- How to detect Potential Induced Degradation(PID) Effect ?
- How to prevent Potential Induced Degradation(PID) Effect ?
What is Potential Induced Degradation (PID) Effect in solar panels?
Potential Induced Degradation (PID) in solar panels originates from a considerable potential difference between the cell's semiconductor and the module's other elements, such as the glass, mounts, or aluminum frame. This variation in voltage leads to a leakage of current, triggering the movement of both negative and positive ions. Negative ions are released through the aluminum frame, while positive ions, notably sodium ions, accumulate at the cell surface. This accumulation effectively compromises the cell, reducing its capacity to harness solar energy, thereby causing a decline in power output. PID can result in notable power losses, possibly up to 20%, and its effects are not immediately visible – it might take from several months to a few years for these effects to become evident.
Why does Potential Induced Degradation (PID) Effect occur?
Potential Induced Degradation (PID) typically emerges in solar photovoltaic systems over extended periods, particularly in environments characterized by high heat and moisture.
High Temperature and Humidity:
The foremost causes of Potential Induced Degradation (PID) in solar panels are elevated temperatures and humidity levels. High humidity contributes to moisture accumulation on the panels, forming conductive pathways that catalyze potential differences, leading to PID. Moreover, increased humidity promotes the movement of charge carriers, causing uneven distribution of current and, consequently, diminished panel performance.
Rising temperatures exacerbate PID by altering semiconductor properties, increasing electron mobility, and accelerating the formation of potential differences, all of which contribute to the material degradation in the panels. The synergy of high humidity and temperature amplifies these effects: humidity enables the adsorption of water vapor on the panels, while elevated temperatures speed up the evaporation process, further intensifying the potential differences.
System Configuration:
The setup of the PV system, encompassing aspects like grounding, module type, and cell type, significantly influences the occurrence of PID. Factors such as the voltage potential and polarity of the module affect PID's likelihood. This dependency is further affected by the panel's position in the array and how the system is grounded. Generally, PID is linked with a negative voltage potential relative to the ground, which makes panels with more negative charge more prone to PID risks.
Loads on the Glass Surface:
The presence of loads on the glass surface of solar panels, such as dust or other contaminants, can heighten the potential difference and thus contribute to the PID effect.
Several elements associated with loads on solar panels play a role in the development of Potential Induced Degradation (PID) effects. When loads accumulate on the surface, they create a thin film, increasing surface resistance and hindering the flow of electrical charges. This leads to concentrated potential differences at the surface, which disrupts the even distribution of electrons and raises the risk of PID. Changes in optical properties caused by loads, like varying light absorption rates, result in uneven absorption and localized potential differences, particularly under intense sunlight. These loads also impact thermal conductivity, leading to local temperature disparities that accelerate the movement of electrons and enhance potential differences, especially in direct sunlight. Loads that absorb moisture can form a conductive path, further speeding up the PID process. Regular cleaning of the panels is essential to minimize these potential differences, sustain panel efficiency, and reduce the likelihood of PID due to surface loads.
How to detect the Potential Induced Degradation (PID) Effect ?
Identifying PID in solar panels involves performing an I-V curve test. PID impairs the performance of solar panels by reducing the shunt resistance in the electrical model (as shown in Figure 1). This reduction correlates with an increase in leakage current, leading to a decrease in the output current (and therefore, the total output capacity). The impact of PID on the I-V curve is demonstrated in Figure 2, where changes in the curve indicate the presence of PID.
Figure 1:One-diode model of a solar panel
Figure 2:I-V curve comparison between PV module affected by PID and not affected by PID
The IEC standard 62804 has been designed to assess the resilience of solar panels against high voltage conditions that could lead to degradation. This standard specifies a testing method where solar panels are subjected to a direct current (DC) voltage bias of 1000 volts, in an environment with 85% relative humidity and at a temperature of 60 degrees Celsius, over a period of 96 hours. The evaluation includes analyzing the panel’s maximum power (Pmpp/W rating), and also involves comparing electroluminescence images of the panel taken before and after the test to detect any changes.
The graphical data reveals that the photovoltaic (PV) system experienced an approximate 25% reduction in power during the PID test. As per the IEC standard 60924, to conform to the established criteria, such a decrease should not exceed 5%. It's important to recognize that while individual solar panels may vary, this standard has been set based on extensive testing across a wide range of PV panels.
How to prevent Potential Induced Degradation (PID) Effect?
The emergence of PID effects can be influenced by various environmental and operational factors. To maintain the stability and efficiency of the solar panel system, several strategies should be implemented to prevent and lessen the impact of PID.
Use solar panels with anti-PID technology:
Opt for solar panels that are designed with anti-PID features. Certain manufacturers incorporate specialized cell technologies to reduce or eliminate the occurrence of PID effects, such as panels utilizing HJT (Heterojunction with Intrinsic Thin layer) technology.
Maysun's HJT solar panels are engineered to prevent Potential Induced Degradation (PID) through the incorporation of a Transparent Conductive Oxide (TCO) film layer on the glass surface. This TCO layer is instrumental in preventing charge polarization, thus effectively averting PID-related degradation. The combination of the heterojunction structure and intrinsic thin layer in Maysun’s HJT panels reduces charge mobility, diminishes uneven current distribution, and substantially lowers the risk of PID, ensuring greater reliability even under demanding conditions. Moreover, these panels have been certified with the Solar Module Test Module PID Resistance-IEC 62804, demonstrating their high-quality standards.
Maysun Solar HJT solar panels have been distributed to several European countries. Customers have shared their satisfaction with the impressive performance and reliability of Maysun HJT solar panels.
Optimize System Design:
Optimizing the system design is crucial in preventing PID effects. Enhancements can be made through:
Maximum Power Point Tracker (MPPT): Utilizing MPPT technology ensures that panels operate at their maximum power point under varying lighting conditions, thereby decreasing the risk of uneven current distribution and slowing the onset of PID.
Current Equalization Technology: Implementing current equalization technology helps in maintaining a uniform current distribution across panels, reducing the likelihood of PID effects due to potential differences.
Protective Coatings:
Applying resistant coatings to solar panels can guard against contaminants and lessen PID risks. These coatings include:
Dust Resistant Coatings: These coatings slow down dust accumulation, keeping the panel surfaces clean.
Water Vapor Resistant Coatings: These prevent water vapor penetration, mitigating the impact of humidity on potential differences.
Anti-Pollution Coatings: They reduce the adherence of substances like grease and bird droppings, preserving the optical clarity of the panel surfaces.
Regular Cleaning:
Frequent cleaning of solar panels is essential for maintaining system efficiency. Removing dust, leaves, bird droppings, and other materials helps keep the surface clean and minimizes the formation of potential differences. Regular cleaning also enhances light transmission and improves the efficiency of light absorption.
Additionally, PID is often reversible. If PID occurs, one solution is to ground the DC negative terminal of the inverter to prevent negative voltages in the string. This method is effective if the inverter supports such operation and all design precautions are taken. Another strategy involves using “anti-PID boxes” between the string and inverter. These devices invert the potential applied by the inverter to counteract negative voltages on the panels, varying the polarization over time to reduce PID likelihood and help modules recover from negative potential.
Since 2008, Maysun Solar has been committed to producing high-quality solar panels. Our diverse range includes half-cut, MBB, IBC, HJT, and shingled solar panels, available in various finishes such as silver, full black, black frame, and glass-glass. These panels feature elegant designs and superior performance, enhancing the appearance of any building. With offices and warehouses worldwide and strong partnerships with leading installers, Maysun Solar is a reliable choice. For inquiries about PV systems or the latest solar panel quotes, contact Maysun Solar; our team is ready to assist you.
Reference:
Greensolver, & Greensolver. (2021b, November 26). Potential Induced Degradation (PID) – What is it? – Greensolver. Greensolver.
Admin-D3v. (2020, July 6). LID vs PID: What’s degrading your solar panels? Raycatch | AI Diagnostics for Solar Energy.
Was ist der PID-Effekt (Potential Induced Degradation) von Solarmodulen? (n.d.). Was Ist Der PID-Effekt (Potential Induced Degradation) Von Solarmodulen?
Causes and solutions of the potential Induced Degradation (PID) effect in PV modules – Technical articles. (2020, July 9).
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