Solar Panel Degradation: What Is It and Why Should You Care?

Photovoltaic (PV) technology has been heavily researched and developed for years. Most PV modules in the industry have a standard lifespan of 25 years, but some leading companies in the solar industry like Maxeon Solar have developed this technology to create solar panels lasting for 40 years or more, covered by a 40-year warranty.

To understand the lifespan limitations of PV modules, you should comprehend the concept of solar panel degradation. This is the main phenomenon affecting the lifespan of PV modules and causing them to break. In this article, we will explain everything you need to know about this and give you tips on how to reduce solar panel degradation.

Studying Solar Panel Degradation

What is solar panel degradation?

Solar panel degradation comprises a series of mechanisms through which a PV module degrades and reduces its efficiency year after year. Aging is the main factor affecting solar panel degradation, this can cause corrosion, and delamination, also affecting the properties of PV materials.

Other degrading mechanisms affecting PV modules include Light-Induced Degradation (LID), Potential-Induced Degradation (PID), outdoor exposure, and environmental factors. There are several tools and techniques used to determine solar panel degradation, these include visual inspection, infrared thermography, electroluminescence (EL), and performance calibration.

While PV technology has been present since the 1970s, solar panel degradation has been studied mainly in the last 25 years. Research Institutes like NREL have estimated that appropriate degradation rates of solar panels can be set at 0.5% per year with current technology.

What is the impact of solar panel degradation on your PV system?

Solar panel degradation is caused by aging and does not only affect large PV installations, but it is present on every rooftop PV installation worldwide. This is why it is of concern for homeowners with rooftop PV systems and households consuming solar energy from the grid.

Appropriate degradation rates of solar panels are estimated at 0.5% per year considering a well-maintained PV system featuring ideal conditions. However, solar panel degradation rates can reach up in some extreme cases, going as high as 1.4% or 1.54% per year.

This information highlights the importance of installing high-quality PV modules manufactured by reliable companies and performing maintenance on solar arrays. Taking every precaution will ensure minimal solar panel degradation rates and a longer lifespan for PV systems.

The higher the degradation rate, the higher energy losses the PV system will experience throughout its lifetime. Solar panel manufacturers generally establish a reference of degradation rates and each module type generally has a performance warranty graph that indicates the expected percentage output against the number of years.

A solar panel with a 0.5% degradation rate per year (Hanwha QCells 400W solar panel for instance in Figure 1) is likely to be somewhere close to 87% of its first-year output at the end of its lifetime. Meanwhile, a low-quality solar panel installed under harsh environmental conditions could have a degradation rate of 1% annually, reducing its output to just about 75% of its first-year output. Top quality manufacturers like SunPower, have been able to reduce degradation rates to as low as 0.25%, providing the maximum performance over time in the industry.

Hanwha Q-Cells 400W Performance Warranty
Figure 1: Hanwha Q-Cells 400W Performance Warranty - Source: Q-Cells
SunPower M Series Performance Warranty
Figure 2: Sunpower M Series Performance Warranty - Source: SunPower

What causes solar panel degradation?

Solar panel degradation is not caused by a single isolated phenomenon, but by several degradation mechanisms that affect PV modules, but the main cause is age-related degradation. Additional causes of solar panel degradation include among others, aging, Light-Induced Degradation (LID), Potential-Induced Degradation (PID), and back-sheet failure. Let us analyze them in more detail.

Age-related degradation

Aging is the main degradation mechanism affecting PV modules throughout their years of operation. This degradation mechanism is a direct consequence of modules being exposed for years to rainfall, snowfall, extreme temperatures, hail, dust, and other external agents.

When PV modules are exposed to the aforementioned external agents, they start to decay over time and reduce their efficiency. This occurs by solar panel frames corroding, glass and back-sheet delamination, and PV materials losing their properties, all of these cause the average 0.5% yearly degradation for PV modules.

Light-Induced Degradation (LID)

Light-Induced Degradation (LID) is a phenomenon causing an acceleration in the degradation rates of solar panels, affecting modules mainly during the first year of operation. This is a consequence of sunlight accelerating the oxidation process between the boron used to dope PV materials and oxygen.

These defects occur naturally as oxygen combines with molten silicon during the Czochralski process used to grow mono-crystalline silicon (mono c-Si). The boron used to dope solar cells combines with oxygen and acts as a trap for electron-hole pairs, impacting the power generation process.

Solar panel degradation caused by LID heavily affects heavily modules manufactured with mono-crystalline silicon, especially p-type wafer ones. LID effect is also higher in PERC modules.

Potential-Induced Degradation (PID)

Potential-Induced Degradation or PID is another degradation mechanism affecting PV modules and reducing their efficiency. Unlike LID, PID does not heavily affect a particular type of PV module, but it affects mono c-Si, polycrystalline silicon (poly c-Si), and thin-film PV modules alike.

Large-scale PV installations feature a high voltage per string which causes a potential difference between the cells and the frame resulting in a leakage current, producing power losses.

Understanding of PID is still incomplete, and further study is required, but it is known that it produces high power losses in ungrounded PV systems featuring voltages over 1,500V. This is associated with large utility-scale and commercial PV systems.

Back-Sheet Failure

Back-sheet failure is another degradation cause, being the main cause of premature degradation. It is determined that 9% to 16% of PV modules suffer from backsheet failure. This is a matter of concern since the backsheet of a PV module is the first line of defense that isolates and protects inner components from external agents like moisture, wind, dust, and ultraviolet (UV) light.

The main cause for solar panel degradation due to back-sheet failure is the delamination of the backsheet or the formation of cracks in the material. When the backsheet fails, the inner components of solar panels are exposed to external agents, and the lifespan of PV modules is reduced.

Which factors increase or reduce solar panel degradation?

Just like there are different degradation rates of solar panels, there are factors that accelerate or reduce solar panel degradation. These include the materials used to manufacture PV modules, assembly process, installation process, maintenance practices, and even the weather.

Quality of Materials

Most PV modules that fall under accelerated solar panel degradation do so because of LID, PID, and back-sheet failure. These degradation mechanisms are partially caused by defects in the materials, so it can be concluded that PV modules with better higher-quality materials degrade at slower rates.

Additional materials and techniques can be used to slow corrosion and reduce solar panel degradation. It has been proven that solar panel systems can last for at least 40 years in degraded conditions, but some groundbreaking companies in the solar industry have improved the technology and are offering PV warranties for 30 years and 40 years.

Assembly of the Modules

PV modules may feature high-quality materials, but they require the strictest manufacturing processes to ensure top performance.

Improving manufacturing techniques may reduce solar panel degradation and extend the lifespan of PV modules. The U.S. Department of Energy Solar Energy Technologies Office is currently funding a research team to develop techniques that could extend the lifespan of PV modules to up to 50 years or more.

Proper Installation

When solar panels are being transported and handled during the installation, modules are subjected to mechanical stress. This stress can cause solar panel degradation due to back-sheet failure and produce partial power losses or compromise the PV module components.

To reduce solar panel degradation caused by cracking on the backsheet and increase the lifespan of PV modules, it is recommended that modules are properly handled and installed by certified professionals. This is especially important when dealing with thin-film solar panels, which are more delicate.

Regular Maintenance

Regular maintenance is a vital tactic used to reduce solar panel degradation in large and small-scale applications. Predictive and preventive maintenance can increase the operational lifetime of PV systems by reducing degradation from soiling and dust, resulting in an increased performance of the solar array.

The frequency at which maintenance should be performed may vary considering the presence of dust, snow, fallen leaves, and other climate conditions. The number of birds in the area (associated with bird drops) may also increase the required maintenance frequency.

Weather

Weather phenomena are not a variable that can be controlled, but they can be accounted for when installing PV modules and performing maintenance to avoid further solar panel degradation. Analysis previous to the installation of large-scale PV systems should consider a dedicated study on the location and historical natural disasters, ensuring the location is feasible for the installation.

An important choice that can be taken when preparing against extreme weather phenomena is selecting PV modules featuring better mechanical properties. This may include a better ingress protection (IP) index, harder frame rating, a glass with higher resistance against impact, and more. For instance, the SunPower PV modules are more vulnerable to high-speed winds compared to Q-Cells solar panels.

Final word: Choosing best PV modules to minimize degradation

Considering that solar panels have a limited lifespan, it is important to note that they can be recycled and repurposed for grid operation, EV charging stations, and other applications. The even better news is that researchers are currently working on extending the lifespan of PV modules and developing techniques to reduce further solar panel degradation.

Studies taking place are looking at increasing durability by relying on electroluminescence photography and machine learning, improving lifespan and performance for PV installation with proven results by implementing monitoring & control systems. Moreover, implementing cooling techniques using water to reduce PV module temperature has also proven effective in extending the lifespan of solar panels.

Many times solar proposals will account for first-year simulations, which may give you a misconception that this energy performance will be maintained over time when it will not. This is why choosing the solar panel with lower degradation rates is essential to keep performance over time as close as possible to the first year of installation. Most solar panel manufacturers include metrics that indicate the performance warranty for their products, choosing high-quality PV modules with degradation rates similar to the ones from SunPower or even Hanwha Q-Cells, will ensure PV systems that resist aging degradation better than conventional ones and that will provide better results in the long term.

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  1. Colin Ng says:

    This was a really informative article. Thanks for all the useful links, and good news such as 40 Year warranties on certain panels, and how well that brand performs in, say, windy conditions.

    I think the only suggestion I would make is to start the y-axis on all graphs at 0, so that the graphs demonstrate the neutral honesty that is present throughout your well-researched and informative article.

    Thanks,

    Colin Ng

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