What is light induced degradation in a solar panel?

Fast read

Solar panels, although lacking moving parts, can degrade over time. Reasons for this deterioration vary, from moisture entering panels due to separated backing sheets to chemical processes like potential-induced degradation.

Light-induced degradation (LID) significantly contributes to this decline, causing a decrease in a solar cell's efficiency upon initial exposure to sunlight. LID primarily affects panels with boron-doped silicon cells, commonly found in crystalline silicon panels.

While newer technologies like N-type solar cells aim to eliminate LID, they remain a concern for many conventional panels. However, LID's impact diminishes over time, with panels typically experiencing a 6-8% efficiency drop after ten years.

Manufacturers provide performance warranties reflecting this reality, ensuring minimal efficiency loss over a solar panel's lifespan. Monitoring system production can help identify efficiency declines, allowing homeowners to address potential warranty claims and maintain optimal solar panel performance.

Do solar panels lose their electricity production capacity over time?

Solar panels aren’t made with moving parts, so they can last for a long time if they have been built well. But they don’t last forever.

There are many reasons solar panels can fail.  I have seen panels where the backing sheet has separated from the front laminate, which allows moisture to enter the panel. Then there are also chemical-related phenomena such as potential-induced degrading of the cells, i.e., the decreasing capacity of individual cells to generate electricity. Although it may take some years for the power drop of the panels via annual degradation to become significant, all solar panels eventually lose efficiency. It’s just that the better-built ones lose less generating power each year than the cheaper ones.

The 25-year power warranty on a solar panel indicates the manufacturer’s trust in its long-term performance. Maybe the best layman’s explanation is to imagine a piece of rubber on a roof exposed to the elements, and the rubber loses part of its elasticity every year due to heat, cold and UV. One reason solar panels lose efficiency in the first place is light-induced degradation (LID). Although it may sound strange that sunlight can cause solar panels to become damaged, this phenomenon is well-known and real.

What is Light-Induced Degradation (LID)?

LID refers to a loss in efficiency in a new solar cell when it is first exposed to sunlight. This is due to the chemistry in the cell, specifically the boron atoms. It happens very quickly. The boron atoms combine with oxygen in the air, causing them to oxidise, reducing the cell’s capacity to generate electricity.  In just a few hours, a brand-new solar panel was exposed to sunlight for as much as 0.5% of its generating capacity for the first time. After this initial exposure and performance loss, the panels will remain relatively stable and only lose the annual estimated percentage mentioned above.

LID effects on different types of solar cells

Conventional solar panels are constructed from pure crystalline silicon. To make silicon conductive and able to convert UV radiation into electricity, the panels are “doped” or infused with boron. Boron is a light element with an atomic number 5. Boron is positively charged, and silicon cells doped with boron can be called P-type. Most of the Monocrystalline technology standard solar panels sold on the Australian market today use P-type crystalline cells.

LID is caused by the presence of these boron atoms when combined with oxygen. This makes it less efficient at producing electricity. The passivated emitter rear cell (PERC) is a high-efficiency-type solar cell invented in Australia. However, the structure of these cells makes them particularly susceptible to LID. This is because P-type PERC cells use more boron doping, which can cause LID. To counter this, panel manufacturers use higher-purity silicon that leaves less oxygen to react with the Boron. This reality presents a technical challenge that can cause PERC cells to have higher LID than other types of panels.

N-type solar cells are one technology that completely avoids the LID issue. Remember I said that p-type solar cells are so named because they contain positively charged Boron atoms? Instead, N-type cells are doped with negatively charged Phosphorus atoms, removing the possible build-up of LID-causing Boron oxide. The LID problem can be eliminated if there is no presence of boron. N-type, a newer technology, has made its way into products like the REC N–Peak series. Jinko also produces an N-type panel, as did LG Electronics, when they made solar panels.

Solar panels with yellow backing sheet
The largest fall in efficiency due to LID typically occurs within the first few hours or days of exposure to sunlight

Should you be concerned about LID?

LID is not something solar homeowners should worry about too much. Solar panels will experience a more significant efficiency drop in the first year for various reasons, including LID. The panel’s degradation becomes slower and steadier after that – so overall, we are talking about a possible performance decrease of 6-8% after 10 years for many panels.  It’s noteworthy but not a strong argument against installing solar panels.

The performance warranty that your solar panel has will reflect this reality. When you research solar, you might notice that two warranties will be offered on a solar panel.  The first, called a Product Warranty, covers defects in the product and, in our opinion, is the key warranty to rely on. The second is called the Performance Warranty and covers the panel’s efficiency, ie, how much generating capacity a panel will lose over its lifetime, often seen as 25 years.

Some panels claim to lose 2% in the 1st year, and others say 3%. Many panels also nominate a further degradation factor after year one, such as 0.5% every year after the 1st year, which usually has the highest degradation factor. Every solar panel we have researched has a performance warranty that allows for a more significant power drop-off in its first year than it does for subsequent years. Most often, warranties guarantee that solar panels won’t lose more efficiency than 2 to 3% in the first year and 0.5 to 0.8% yearly. You can check the degradation factor of your panels by studying their datasheet or performance warranty, where this information is revealed. Check out to Your Energy Product section, this is where you can find your products datasheet.

What does this all mean for solar homeowners?

You can monitor your system’s production over time. Most monitoring solutions, either as part of the inverter package or as a self-contained monitoring solution, such as Solar Analytics, allow you to see your solar system’s daily, monthly and annual kWh output performance. So, if you experienced similar weather over 2 years and your production numbers have been much lower in the 2nd year, you could have seen a higher-than-expected panel degradation.

While there are other potential reasons for this production loss, for example, you have 2-panel strings, and one has had a malfunctioning connection point, it is certainly something to investigate. Higher quality monitoring software will also send you warnings, for example, via email, if your system’s performance is lower than it should be – using historical weather data. If your system is not producing the same output levels as it used to, and if there has been a significant drop in panel efficiency, you could consider filing a warranty claim with the panel manufacturer.

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