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Multiple factors affect the productive lifespan of a residential solar panel. In the first part of this series, we will look at the solar panels themselves.
Residential solar panels are typically sold with long-term loans or leases, with homeowners signing contracts of 20 years or more. But how long do the panels last and how resistant are they?
The useful life of the panels depends on several factors, such as the climate, the type of module and the shelving system used, among others. Although there is no specific “end date” for a panel itself, loss of production over time often forces equipment to be retired.
When deciding whether to keep your panel operational in 20-30 years or look for an upgrade then, the best way to make an informed decision is to monitor production levels.
Degradation
According to the National Renewable Energy Laboratory (NREL), the loss of power over time, called degradation, is usually around 0.5% per year.
Manufacturers typically consider 25 to 30 years to be the time when sufficient degradation has occurred to consider replacing a panel. The industry standard for manufacturing warranties is 25 years on a solar module, NREL said.
Taking into account the reference annual degradation rate of 0.5%, a 20-year panel is capable of producing around 90% of its original capacity.
The quality of the panels can influence degradation rates. According to NREL, premium manufacturers such as Panasonic and LG have rates of around 0.3% annually, while some brands degrade as much as 0.80%. After 25 years, these premium panels could still produce 93% of their original performance, and the most degraded example could produce 82.5%.
A considerable portion of the degradation is attributed to a phenomenon called potential-induced degradation (PID), a problem experienced by some panels, but not all. PID occurs when the voltage potential and leakage current of the panel cause the mobility of ions within the module between the semiconductor material and other elements of the module, such as the glass, support, or frame. This causes the power output capacity of the module to decrease, in some cases significantly.
Some manufacturers build their panels with PID-resistant materials in the glass, encapsulation, and diffusion barriers.
In addition, all panels suffer from so-called light-induced degradation (LID), which causes them to lose efficiency in the first hours of exposure to the sun. Light-induced degradation varies from panel to panel depending on the quality of the crystalline silicon wafers, but typically results in a single efficiency loss of 1 to 3%, according to PVEL testing laboratory, PV Evolution Labs.
Weather
Exposure to weather conditions is the main factor in the degradation of panels. Heat is a key factor in both real-time panel performance and its degradation over time. Ambient heat negatively affects the performance and efficiency of electrical components, according to NREL.
By consulting the manufacturers technical data sheet, you can find out the temperature coefficient of a panel, which will demonstrate its ability to perform at higher temperatures.
The coefficient explains how much real-time efficiency is lost for each degree Celsius rise above the standard temperature of 25 degrees Celsius. For example, a temperature coefficient of -0.353% means that for every degree Celsius above 25, 0.353% of total production capacity is lost.
Heat exchange drives the degradation of the panels through a process called thermal cycling. When it is hot, materials expand, and when the temperature drops, they contract. This movement causes microcracks to form in the panel over time, which reduces production.
In its annual Module Score Card study, PVEL analyzed 36 operational solar projects in India and found significant effects of thermal degradation. The average annual degradation of the projects was 1.47%, but installations located in colder mountain regions were degraded by almost half, 0.7%.
Proper installation can help solve heat-related problems. The panels should be installed a few centimeters above the roof, so that convective air can flow underneath and cool the equipment. Light-colored materials can be used in the construction of the panels to limit heat absorption. And components such as inverters and combiners, whose performance is especially sensitive to heat, should be placed in shaded areas, suggests CED Greentech.
Wind is another weather condition that can damage solar panels. Strong wind can cause panels to bend, which is called dynamic mechanical loading. This also causes microcracks in the panels, which reduces production. Some shelving solutions are optimized for high wind areas, protecting panels from strong lifting forces and limiting microcracks. Normally, the manufacturers technical sheet provides information on the maximum winds that the panel can withstand.
The same goes for snow, which can cover the panels during the strongest storms, limiting production. Snow can also cause dynamic mechanical loading, degrading the panels. Snow usually slides off the panels as they are slippery and get hot, but in some cases the homeowner may decide to remove snow from the panels. This must be done carefully, as scratching the glass surface of the panel would have a negative impact on performance.
Degradation is a normal and inevitable part of a panels life. Proper installation, careful snow removal, and careful cleaning of the panel can help improve production, but ultimately a solar panel is a technology with no moving parts, requiring very little maintenance.
Standards
To ensure that a given panel has a long life and performs as intended, it must undergo standard testing for certification. The panels undergo International Electrotechnical Commission (IEC) testing, which applies to both monocrystalline and polycrystalline panels.
According to EnergySage, panels that meet IEC 61215 are tested for electrical characteristics such as wet leakage currents and insulation resistance. They are subjected to a mechanical load test, both wind and snow, and to climatic tests that verify their resistance to hot spots, exposure to UV rays, humidity and cold, humid heat, the impact of hail and other outdoor exhibitions.
The IEC 61215 standard also determines the performance parameters of a panel under standard test conditions, such as temperature coefficient, open circuit voltage, and maximum output power.
It is also common to see the Underwriters Laboratories (UL) seal on a panels specification sheet, which also provides standards and testing. UL performs weather and aging tests, as well as the full range of safety tests.
Failures
The failure rate of solar panels is low. NREL conducted a study of more than 50,000 systems installed in the United States and 4,500 worldwide between 2000 and 2015. The study found an average failure rate of 5 panels in every 10,000 annually. |
