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PID: Causes, Impacts, Mitigation and vs. Other Effects

PID is a phenomenon in solar panels that can adversely affect energy production and more. 

Besides its impacts, this article will delve into its causes and mitigation. Through a comparison with other effects in solar panels, you will acquire a deep understanding of PID and how to make a panel and system function at its best, and consequently, make the most of your investment.

Solar Panel Inspection

What is PID in Solar Panels?

Typically, electricity generated by solar cells flows through a network of metal contacts including fingers, busbars and ribbons along a predetermined path. The electricity is then collected and transmitted through the connected wires of the panel, ultimately feeding into an inverter or powering loads.

However, sometimes, electrical currents may not always flow in a predictable pattern.

Potential Induced Degradation (PID) is a phenomenon that occurs when part of the electricity in the panel moves through the coating, encapsulant material or frame rather than flowing along the defined path. As its name suggests, PID can cause degradation in efficiency and output.

The Causes of PID

PID in solar panels results from several factors. They are mainly related to the electrical stress placed on the panel and the surrounding conditions of the currents.

High System Voltages

When solar power systems operate at high voltages that are up to 1,000V or 1,500V, a large electrical potential difference between different parts of the solar panel can occur. This kind of difference especially exists between the panels and the frame, or between the panels and the grounded parts of the power system.

The electric field stress due to this differential can then drive ions, especially sodium ions (Na+) from the glass surface toward the semiconductor layer or other sensitive regions, causing degradation.

Environmental Conditions

Environmental factors such as high temperatures and humidity levels can accelerate the movement of ions within the panels, and as a result, amplify the degradation process.

Material Properties

Encapsulants like Ethylene Vinyl Acetate (EVA), if in lower quality, can be prone to moisture and contaminant ingress over time. This facilitates the movement of ions as well, and consequently, exacerbates PID.

Furthermore, front covers, which are usually in the form of glass, can contain a larger amount of sodium ions when manufactured with substandard materials, increasing the likelihood of PID occurrence. Lower-quality anti-reflective coatings can worsen the process as well.

System Configuration

Solar panels at the negative end of the string typically experience higher negative potentials relative to the grounded structure, making them more prone to PID.

The use of transformerless inverters (both string and micro inverters have transformerless models) can also raise the stakes for PID compared to the use of inverters with transformers, as transformerless inverters do not provide galvanic isolation.

Improper System Design & Installation

Improper design and installation of panels can lead to prolonged shading, which can develop localized high potentials and drive PID effects.

Whereas the way the panel frame is designed and grounded can influence the development of PID. Improper grounding methods will influence the potential differences across the panels, with certain configurations increasing the risk of PID.

In What Installations Can PID More Easily Occur?

Based on their causes, PID is more likely to occur in these installations:

Large-Scale Solar Power Farms

These solar power systems often operate at higher voltages to improve efficiency and reduce transmission losses. However, higher voltages increase the electrical potential differences, making the system susceptible to current leakage and PID.

Projects Using Transformerless Inverters

Transformerless inverters are commonly used in small-scale or cost-sensitive projects because of their higher efficiency and lower cost. However, transformerless inverters generally lack galvanic isolation which increases the risk of PID.

Projects in Humid or High-Temperature Environments

Projects located in tropical/subtropical regions or coastal areas are more likely to experience PID, as high humidity and temperature accelerate the movement of ions within the panels.

Older Installations

After many years of operation, materials such as encapsulants and sealants may deteriorate. Meanwhile, panels used in these projects are less likely to incorporate modern PID-resistant technologies and materials. Hence, older installations may be more susceptible to PID.

What Are the Impacts of PID?

PID can significantly affect the performance and longevity of solar power systems. 

Reduction in Power Production

The affected cells will experience a drop in their efficiency and generate less electricity. This ultimately degrades the overall power production of the solar system, ranging from a few percentage points to over 30%; some research even recorded an 80% loss.

Degradation of Components

The occurrence of PID, involving both physical and chemical processes, can compromise the structure integrity of the cells. This can cause micro-cracks, delamination and other forms of wear and tear. In some cases, PID can further induce the failure of bypass diodes, which worsen the situation and impact overall production.

System Reliability

Continuous PID effects can lead to long-term degradation, reducing the lifespan of the solar panels and the overall system.

Under circumstances when PID is particularly severe, complete shutdowns for the system may be necessary for assessment and repair, leading to operational downtime and huge production losses.

Financial Impacts

Degraded production directly corresponds to reduced revenue for homeowners or solar power farm operators. On the other hand, addressing PID may require additional maintenance efforts, component replacements or retrofitting with PID-resistant technologies, all of which incur costs.

As a whole, decreased performance further extends the payback periods for the projects, and lowers their Return on Investment (ROI) or resale value.

Environmental Impacts

Lower efficiency and potential early panel replacements mean that more resources are required to manufacture additional panels. This is translated to reduced green energy production, higher manufacturing emissions and a higher lifecycle carbon footprint.

How to Mitigate PID?

The degradation can occur rapidly, sometimes within days or weeks after installation. Certain strategies needed to be implemented to avoid and at least minimize it.

Go For High-Quality Components

The fundamental strategy is to use solar panels meeting high standards such as IEC 62804 and with top-grade PID-resistant materials for your project. These panels integrate high-quality encapsulants and anti-reflective coatings, and can withstand harsh environmental conditions and reduce the likelihood of PID.

Optimize System Design

Reducing the overall system voltage can help mitigate the electrical stress that contributes to PID. Meanwhile, employing proper grounding techniques can minimize the potential differences that cause PID.

If budget allows, adopt transformer-based inverters for your project since they provide galvanic isolation and help to reduce PID risk.

Proper Installation

Avoid installing solar power systems in highly humid or saline environments. 

If this is not possible, ensure that the installation is done correctly with proper grounding and without shading. Utilize effective ventilation strategies and design to ensure good airflow for the operation of the panels.

Maintenance and Monitoring

Regular cleaning of solar panels to remove dust, dirt and other contaminants can bring down the occurrence of hotspots and mismatch, which can contribute to the development of PID.

Employing advanced monitoring systems aids in the detection of PID. This can be done with the panel-level monitoring functionality of microinverters. IV curve tracing, electroluminescence imaging and thermography are also professional ways to detect PID.

Adopt Innovative Technologies

Combine the use of anti-PID equipment such as charge equalizers, which can be either separate devices or built-in modules of advanced inverters.

When the inverter is not active, the anti-PID equipment applies a controlled DC bias to the solar panel array. This bias is opposite to the polarization voltage that causes PID. As the depolarization current flows, the polarization charge is reversed, and the PID effect is mitigated.

How Does PID Compare With Other Effects in Solar Panels?

By now, you may have encountered various effects in solar panels, leaving you wondering about their causes, impacts, relationships and more. To give you a better understanding, the following chart offers a concise comparison of their similarities and differences.

AspectPIDHotspot EffectMismatch
Primary CauseLeakage currents due to high voltageShading, defects, or uneven agingVariations in electrical characteristics
EffectsSignificant power loss, cell degradationLocalized overheating, potential damageReduced efficiency, potential hotspots
MitigationHigh-quality materials, anti-PID solutionsBypass diodes, regular cleaning, ventilationBinning, DC optimizers, proper design
SeverityCan lead to 30-80% power lossCan cause severe damage and safety risksLimits overall system performance

PID, hotspots and mismatch all reduce solar panel efficiency and system output. 

Actually, the three can influence each other. PID deteriorates cell performance, potentially leading to mismatch and creating hotspots due to uneven power production. Similarly, hotspots and mismatched conditions can stress cells further, exacerbating PID and overall system inefficiency.

Final Verdict

PID is a critical issue in solar power systems, causing significant efficiency and production losses, financial impacts and reduced longevity of solar panels. 

Understanding the causes, impacts and effective mitigation strategies is essential.

Implementing PID-resistant materials, optimal system design and regular maintenance can mitigate PID. 

Addressing PID effectively ensures sustainable and efficient solar energy production, safeguarding both financial and environmental investments.

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