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Detailed reviews and information of the best solar panels, inverters and batteries. Plus hybrid and off-grid solar system reviews and information articles on how solar and battery systems work.

Solar Panel Warranty

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 Solar Panel Warranty

For those new to solar, understanding solar panel warranties can be quite confusing due to the two very distinct warranty conditions, a product warranty and a performance warranty. Like most products and appliances, solar panels have a manufacturer’s product warranty that protects against any failures due to faulty materials or workmanship. Solar panels also have a secondary warranty condition, known as the performance warranty which accounts for a slight loss in performance or degradation over the life of the panel.

1. Product Warranty

The product warranty is the manufacturer’s warranty that protects the customer against defects that may have occurred due to manufacturing errors, quality issues, or component and material failures. This means the manufacturer must either replace or provide a refund for solar panels which fail within the product warranty period. In general, solar panel manufacturers must provide a minimum 10-year product warranty period, however, a growing number of premium manufacturers now offer 15, 20 and even 25-year product warranties.

2. Performance Warranty

The performance warranty also referred to as the power output warranty ensures that the solar panel still produces a minimum amount of power output after the expected 25-year life of a panel. Once installed outside and exposed to sunlight, UV radiation, high temperatures and extreme weather, all solar panels will slowly reduce power output over time. Typically, 2% is lost in the first year, while the annual loss over the remaining 24 years is typically much less, at around 0.5% to 1.0% per year.

The industry standard is 80-84% power output retained after 25 years. However, some high-end manufacturers, such as Sunpower, LG, and REC guarantee as much as 88% to 92% remaining power output on most modules after 25 years of use. There is also a growing number of manufacturers offering 30-year performance warranties on the unique dual glass and bifacial solar modules.


Solar Panel Warranty Comparison Chart

The yellow line indicates the minimum power rating after 25 years of use as specified under the various manufacturer’s performance warranty documents. Note, without an obvious defect it is almost impossible to determine if the rated power output of a panel is within tolerance without specialised equipment. With this in mind, we recommend taking the manufacturers reputation and service history into consideration. A local support office or service centre should also be a must.

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Performance warranty explained

Rooftop mounted solar panels are generally very reliable, have no moving parts and require very little maintenance. However, it is normal for the solar PV cells to slowly break down and suffer from a small amount of degradation. Solar panels are expected to perform under a wide variety of very extreme environments, from freezing winter conditions to very high summer temperatures, high humidity, wind, and severe UV radiation, not to mention salt mist corrosion in coastal seaside locations. Due to these extreme conditions, all solar panels experience some minor degradation over time due to several known phenomena explained below.

 
 

Degradation rates vary significantly depending on the type of cell substrate used by the manufacturer of which there are two main types, P-type and N-type. Panels with the least amount of degradation are those built with a high-grade N-type silicon substrate. These high-performance N-type cells have a lower rate of light induced degradation and can expect to lose only 0.5% per year, which equates to close to 90% retained power output after 25 years of use. Due to the lower cost of production, most manufacturers use P-type cells which have a slightly higher rate of degradation at approximately 0.8% per year.

PID - Potential Induced Degradation

Potential induced degradation is a form of panel degradation which can occur after several years of use due to high voltage, elevated temperatures and humidity. PID is essentially a voltage leak from the cells to the frame of the solar panel resulting in reduced voltage and power loss. Most rooftop solar arrays operate in the 300 to 600V volt range and PID is more prominent with higher string voltages, therefore the more panels connected in a string, the greater the chance of PID occuring. Large scale solar farms often operate in the 1000 to 1500 volt range so the chance of PID is much higher. In very serious cases, after 10+ years, the power can be severely affected with up to 50% string power loss. Fortunately, many of the leading manufacturers have virtually eliminated the risk of PID, however it’s still an ongoing problem as highlighted by the latest test results from independent testing institutions like PVEL.

LID - Light Induced Degradation

When a solar panel is first exposed to sunlight a phenomenon known as ‘power stabilisation’ occurs due to traces of oxygen in the silicon wafer. This effect is well studied and is the initial phase of light induced degradation, or LID, known as the stablisation phase. A solar panel can lose up to 3% of its rated wattage (Wp) output in the first few hundred hours of operation and the full effect of this initial phase occurs during the first year of use.

After the initial stablisation phase, the rate of LID reduces significantly down to 0.5% to 0.8% per year for the next 25+ years. Fortunately, most manufacturers have factored the initial LID effect into the production process. To ensure the rated panel power (Wp) is still maintained after the initial LID phase, panels are often rated up to 5% higher than the nameplate Wp rating. For example, a 350 Watt panel, may initially produce up to 5% more power, or up to 368 Watts for a short amount of time. However, this slight over production is generally very short lived and may not be measurable unless the panels are operating under the ideal (STC) conditions.

 
Performance warranty comparison chart - LG use high grade cells to ensure the least amount of degradation over the expected 25 lifetime

Performance warranty comparison chart - LG use high grade cells to ensure the least amount of degradation over the expected 25 lifetime

 

General degradation

Example of solar panel backsheet cracking and delamination after 10 years

Example of solar panel backsheet cracking and delamination after 10 years

In addition to the well known PID and LID effects, panels can also suffer from more serious issues due to a breakdown of the encapsulant and protective layers which are supposed to protect the cells from the elements. The most common of these is back-sheet failure. While the front glass sheet protects the solar cells from rain, hail, dirt and debris, the white plastic back-sheet is designed to protect the rear side of the cells from water, humidity and scuffs. However, often due to substandard material selection and poor quality control, UV radiation can cause the rear protective back-sheet can breakdown, crack or degrade over time. This degradation can then lead to more serious issues such as moisture ingress, corrosion and earth leakage.

LeTID

Most modern silicon crystalline solar panels contain PERC solar cell technology which increases panel efficiency and has been adopted by the majority of the world’s solar panel manufacturers. However, it has only recently become apparent that P-type PERC cells can suffer what is known as LeTID or light and elevated temperature induced degradation.

The LeTID phenomenon is similar to LID although the losses due to LeTID have been recorded to be as high as 6% in the first year and if not fully accounted for by the manufacturer could lead to poor performance and potential warranty claims. Fortunately N-type silicon cells from several manufacturers including LG, Sunpower and REC do not suffer the effects of LeTID. Also several manufacturers who use P-type poly and mono PERC have developed processes during manufacture to reduce or eliminate any LeTID losses, this includes Q Cells who are the first to claim anti-LeTID technology on all panels.

Many of the worlds leading manufacturers including Jinko Solar Trina Solar, Longi Solar and GCL have all recently gained certification against LeTID from TÜV Rheinland. Other who also claim to have reduced or accounted for the effect of LeTID include REC, Winaico and Canadian Solar. See the latest updates and information on manufacturers meeting the challenges of LeTID in the detailed articles from PV Tech.

How to know if your solar panels are working correctly?

Unless there are obvious signs of panel failure, such as cracked glass, it is often very difficult for an untrained person to determine if a solar panel is operating at its expected level. When a solar panel is manufactured, the power output is measured using a high powered flash test producing exactly 1000W per square meter of light in a controlled environment at a temperature of 25°C. However, it is very hard to obtain accurate measurements in the real world as the panel surface temperature is typically much higher than 25°C when exposed to sunlight, plus the amount of sunlight (solar irradiance) can vary significantly depending on the season, time of day, dust, smog, atmospheric losses and other factors.

For the reasons explained above, the best way to measure your solar performance is to check the daily production level (kWh) of the solar system and compare it to previous days, months and years. Most modern solar systems have some form of system monitoring that measures the amount of solar generation. This data is often logged in an App or online portal which can be used to assess the performance over time. This can also be compared to other systems in your area but be sure to account for the orientation of the solar panels as this can greatly affect the outcomes. Solar Analytics is a third party add-on device that has the ability to analyse your solar performance and alert you of any performance issues.

Solar system monitoring using solar analytics can help determine whether your solar system is operating correctly.

Solar system monitoring using solar analytics can help determine whether your solar system is operating correctly.

Coming soon: How to make a warranty claim, Solar panel maintenance, Mounting locations, panel clamping zones.