L R AS Published on Monday 20 September 2021 - n° 374 - Categories:fundamentals PV
Lifetime of residential solar panels
The life of the panels depends on several factors: climate, type of panel and the racking system used, among others. Production loss over time, estimated at 0.5% per year,
often requires the equipment to be removed. Manufacturers generally consider that after 25 to 30 years, there is sufficient degradation to consider replacing a panel. A 20 year old panel has a production rate of 90% of its original capacity.
The quality of the panels has an impact on the degradation rate. High-end panels such as Panasonic and LG have rates of about 0.3% per year, while some brands have degradation rates as high as 0.8%.
Some manufacturers build their panels with PID resistant materials in their glass, encapsulation and diffusion barriers. A significant portion of the degradation is attributed to a phenomenon called potential induced degradation (PID). This is a problem encountered by some, but not all, panels. It occurs when the panel's voltage potential and leakage current cause ionic mobility within the panel between the semiconductor material and other elements of the panel, such as the glass, substrate or frame.
All panels also experience what is known as light-induced degradation (LID), which results in a loss of panel efficiency in the first few hours of exposure to sunlight. This varies from panel to panel depending on the quality of the wafers and crystalline silicon, but generally results in a one-off loss of efficiency of 1 to 3%, according to the PVEL test laboratory.
Exposure to weather conditions is the main factor in panel degradation. Heat is a key factor in both the real-time performance of the panel and its degradation over time. Ambient heat adversely affects the performance and efficiency of electrical components, according to NREL.
Heat exchange also leads to degradation through a process called thermal cycling. When it is hot, materials expand; when the temperature drops, they contract. This movement slowly causes micro-cracks to form in the panel over time, reducing efficiency. The coefficient explains the loss of efficiency for each degree Celsius above the standard temperature of 25 C. For example, a temperature coefficient of -0.353% means that for every degree Celsius above 25°, the panel loses 0.353% of the total production capacity.
Wind is another weather condition that can cause damage to solar panels. Strong wind can cause the panels to bend, known as dynamic mechanical loading. This also causes micro-cracks in the panels, which reduces the yield. Some racking solutions are optimised for high wind areas.
The failure rate of solar panels is low. NREL conducted a study of more than 50,000 systems installed in the US and 4,500 worldwide between 2000 and 2015. The study found a median failure rate of 5 in 10,000 panels per year. This failure rate has halved since 2000.
System downtime is rarely attributed to panel failure. 80% of solar plant downtime is due to inverter failure,
PV Magazine of 14 September 2021