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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 often sold with long-term loans or leases, lasting 20 years or more. But how long do the panels last and how resilient are they?
The lifespan of panels depends on several factors, including climate, module type, and racking system used, among others. While there is no specific “expiration date” for a panel itself, loss of production over time often forces the equipment to be retired.
When deciding whether to keep your panel running in 20-30 years or look into upgrading at that time, the best way to make an informed decision is to monitor output levels.
Degradation
According to the National Renewable Energy Laboratory (NREL) , power loss over time, called degradation, typically occurs at a rate of about 0.5% per year.
Manufacturers typically consider 25 to 30 years to be the point at which enough degradation has occurred to warrant replacing a panel. “The industry standard for manufacturing warranties is 25 years on a solar module,” NREL said.
Considering the reference annual degradation rate of 0.5%, a 20-year-old panel can produce approximately 90% of its original capacity.
Panel quality can influence degradation rates. According to NREL, top-tier manufacturers such as Panasonic and LG have rates of about 0.3% per year, while some brands degrade as much as 0.80%. After 25 years, these top-tier panels could still produce 93% of their original output, and the highest-degrading model could produce 82.5%.
A significant portion of degradation is attributed to a phenomenon called potential-induced degradation (PID), a problem experienced by some, but not all, panels. PID occurs when the panel voltage potential and leakage current cause ion mobility within the module between the semiconductor material and other elements of the module, such as the glass, carrier, or frame. This causes the module’s power output capability 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 light-induced degradation (LID), whereby they lose efficiency in the first few hours of exposure to sunlight. 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 testing laboratory PVEL, PV Evolution Labs.
Outdoor
Exposure to weather conditions is the primary driver of panel degradation. Heat is a key factor in both real-time panel performance and panel degradation over time. Ambient heat negatively impacts the performance and efficiency of electrical components, according to NREL.
By consulting the manufacturers data sheet, you can find out the temperature coefficient of a panel, which will demonstrate its performance capacity at higher temperatures.
The coefficient explains how much real-time efficiency is lost for every degree Celsius increase 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 panel degradation through a process called thermal cycling. When its hot, the materials expand, and when the temperature drops, they contract. This movement causes microcracks to form in the panel over time, reducing 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 facilities located in cooler mountainous regions degraded by almost half as much, at 0.7%.
Proper installation can help solve heat-related problems. Panels should be installed a few centimetres above the roof, so that convective air can flow underneath and cool the equipment. Panels can be made from clear materials to limit heat absorption. And components such as inverters and combiners, whose performance is particularly 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 mounting solutions are optimized for high wind areas, protecting the panels from strong lifting forces and limiting microcracks. Typically, the manufacturers data sheet provides information on the maximum winds that the panel can withstand.
The same goes for snow, which can cover the panels during the heaviest storms, limiting production. Snow can also cause dynamic mechanical loading, degrading the panels. Typically, snow slides off the panels as they are slippery and heat up, but in some cases the owner may decide to remove the snow from the panels. This should be done carefully, as scratching the glass surface of the panel would have a negative impact on performance.
Degradation is a normal and unavoidable part of a panels life. Proper installation, careful snow removal, and meticulous panel cleaning can help improve output, but ultimately a solar panel is a technology with no moving parts, requiring very little maintenance.
Rules
To ensure that a given panel has a long lifespan and performs as intended, it must undergo standard testing for certification. 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 also undergo a mechanical load test, both wind and snow, and weather tests that check their resistance to hot spots, UV exposure, humidity and cold, damp heat, hail impact, and other outdoor exposures.
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 testing, as well as the full range of safety testing.
Faults
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 five panels per 10,000 per year.
Panel failures have improved significantly over time, with systems installed between 1980 and 2000 found to have a failure rate twice that of the post-2000 group.
(Read: “ The best brands of solar panels in performance, reliability and quality ”)
System downtime is rarely attributed to panel failure. In fact, a study by kWh Analytics found that 80% of solar plant downtime is due to failure of the inverters, the device that converts direct current from the panel into usable alternating current. |
