PID in Solar Panels: Causes, Effects, and Prevention

Introduction

Solar panels are exposed to electrical, thermal, and environmental conditions throughout their operation. Over time, these conditions may influence the electrical performance and reliability of a photovoltaic module. Potential induced degradation (PID) in solar panels is one such degradation mechanism that is associated with electrical potential differences within a PV system.

PID in solar panels may develop gradually, so its impact is not always immediately visible during a routine inspection. Understanding the issue is useful for solar system designers, installers, and owners who want to maintain expected energy generation.

Let's learn what PID is, how it can be identified, what causes it, the PID effect on solar panels, and the measures used to prevent it.

What is PID in Solar Panels and How Can it Be Identified?

PID in solar panels refers to a degradation mechanism in photovoltaic modules caused by electrical potential differences between the solar cells and other parts of the module or system. These voltage differences can result in leakage currents and changes in the electrical behaviour of cells. The exact mechanism can vary according to cell technology, module materials, polarity, and operating conditions. National Renewable Energy Laboratory (NREL) has also studied PID extensively and contributed to the development of standardised testing methods under IEC TS 62804-1.

The condition may be difficult to identify through visual inspection alone. A technical assessment can involve several methods:

1. Monitoring Power Output: A gradual or unexpected reduction in energy generation can indicate that a module or string needs further investigation. Performance should be compared with irradiance, temperature, and other operating conditions before concluding.
2. Comparing String Performance: If one string produces substantially less electricity than comparable strings under similar conditions, technicians can investigate the affected modules for possible degradation.
3. Testing I-V Characteristics: I-V curve testing measures the current and voltage behaviour of a PV module or array. Changes in parameters such as maximum power and voltage can provide useful diagnostic information. NREL testing has documented PID-related changes in module power and voltage characteristics.
4. Using Electroluminescence (EL) Imaging: EL testing can reveal cell-level changes that may not be visible under normal conditions. It is generally performed as part of a specialist diagnostic assessment.
5. Reviewing Operating Conditions: System voltage, temperature, humidity, grounding arrangements, and module construction should be considered when investigating suspected PID.

What Causes PID in Solar Panels?

Several factors can contribute to the development of PID in solar panels. The exact combination varies between module technologies and system designs.

1. High System Voltage

   A high electrical potential between the module circuit and grounded components can increase the stress associated with PID. The applied voltage is also an important part of standard PID testing procedures.

2. High Temperature and Humidity

   Accelerated PID assessments commonly apply high voltage under controlled heat and humidity. IEC TS 62804-1 chamber testing typically uses 60°C, 85% relative humidity, and 96 hours of exposure. Some research studies use more severe conditions.

3. Moisture Exposure

   Moisture can influence leakage paths within a module and interact with its materials. Encapsulants and backsheets play important roles in protecting internal components from environmental exposure. International Energy Agency Photovoltaic Power Systems Programme (IEA PVPS) identifies material interactions, including those involving moisture and encapsulant degradation products, as relevant to module degradation.

4. Module Material Properties

   Encapsulant, backsheet and other module materials influence electrical and environmental behaviour. Their properties can affect how a module responds to the conditions associated with PID.

5. Solar Cell Technology

   Different cell structures can have different sensitivities to PID. Recent IEA PVPS research has examined PID mechanisms in technologies including Passivated Emitter Rear Totally Diffused (PERT) and Tunnel Oxide Passivated Contact (TOPCon) cells. This shows that the response can depend on cell structure and passivation materials.

6. System and Grounding Configuration

   The relationship between module polarity, system voltage, inverter configuration, and grounding can influence the electrical conditions experienced by modules. Proper system design therefore plays an important role in reducing exposure to PID-related stresses.

What are the Effects of PID in Solar Panels?

The effects can vary according to the degradation mechanism, module construction, and severity. Common impacts of PID in solar panels include:

1. Reduced Power Output

   The most important practical effect is a decline in the module's ability to produce its rated electrical power. Testing has shown that some modules can experience measurable power degradation under PID stress.

2. Changes in Voltage Characteristics

   PID may affect electrical parameters such as maximum power voltage. NREL testing has recorded power losses that were largely associated with changes in voltage rather than current in certain affected modules.

3. Lower Fill Factor

   Certain PID mechanisms can increase shunting within cells, affecting the shape of the I-V curve and reducing the fill factor. This can contribute to lower module output.

4. Uneven String Performance

   PID may affect modules to different degrees. As a result, some strings may show greater performance losses than others, making string-level monitoring useful for identifying unusual behaviour.

5. Cell-level Degradation

   Electrical and material changes associated with PID may produce detectable cell-level defects. EL imaging can help technicians investigate these changes when a module requires detailed assessment.

6. Higher Energy Losses at System Level

   When affected modules remain in service with reduced output, the cumulative loss in energy generation can become significant. IEA PVPS has identified PID among PV module failure modes that can have a substantial impact on system power loss.

How Can PID in Solar Panels Be Prevented?

Prevention begins with module selection and continues through system design, installation, and monitoring. The following measures are commonly considered:

1. Select Modules Tested for PID Resistance

   Module specifications should include appropriate PID testing. IEA PVPS recommends checking modules tested according to IEC 62804-1 and verifying that the tested bill of materials corresponds to the modules being installed.

2. Assess the System Voltage

   System designers should consider the voltage stress experienced by individual modules and ensure that the selected components are suitable for the intended system configuration.

3. Choose Compatible System Components

   Module, inverter, and grounding arrangements should be assessed together. An appropriate configuration helps maintain the electrical conditions specified by the equipment manufacturer.

4. Follow Correct Grounding Practices

   Proper earthing and electrical installation practices are important for maintaining safe and intended system operation. Design and installation should follow applicable standards and manufacturer instructions.

5. Consider the Operating Environment

   Locations with high humidity, elevated temperatures, or other demanding environmental conditions may require additional attention during module selection and system design.

6. Monitor System Performance Regularly

   Ongoing monitoring can help identify unusual changes in generation. Early investigation provides an opportunity to determine the cause and take appropriate corrective action.

7. Assess Suspected Degradation Professionally

   If testing confirms PID, corrective options depend on the type and severity of degradation. IEA PVPS notes that some early-stage cases may respond to recovery methods, while progressed degradation may require module replacement with PID-resistant modules.

Maintaining Reliable Solar Panel Performance

PID in solar panels is a degradation mechanism that requires attention during module selection, system design, and performance monitoring. Electrical potential differences, environmental conditions, module materials, and cell technology can influence its development.

At Eastman Auto & Power Limited, we offer solar panels designed with PID-resistant technology to support reliable performance and long-term energy generation. Selecting modules with appropriate PID testing and following sound electrical design and installation practices can help reduce associated risks. Regular monitoring and timely technical assessment also support better maintenance decisions and help identify performance issues at an early stage.

With suitable module selection and proper system practices, solar installations can maintain dependable electricity generation under their intended operating conditions.