Quick Answer
Some solar panels are rated for higher efficiency loss because they have a more aggressive temperature coefficient, which means they lose more efficiency as temperature increases, or because they use a different type of panel material that degrades at a faster rate.
Temperature Coefficient Impact
Temperature is a significant factor in solar panel efficiency. The temperature coefficient measures how much a solar panel’s efficiency decreases with a 1°C increase in temperature. Most high-efficiency solar panels have a temperature coefficient around -0.3 to -0.5% per °C, but some panels may have a coefficient as high as -0.6% per °C. This means that for every 1°C increase, the panel’s efficiency can decrease by 0.6% if it has a high temperature coefficient.
Material Degradation
The material used in solar panels can also affect their efficiency loss over time. For example, PERC (Passivated Emitter and Rear Cell) solar panels have been shown to degrade more quickly than mono-crystalline silicon panels, with an LID (Light-Induced Degradation) rate of around 1-2% after 1,000 hours of exposure to sunlight. This can result in a higher efficiency loss over the panel’s lifespan. Manufacturers may use different materials or designs to achieve higher efficiency ratings, but these materials may degrade at a faster rate.
Panel Degradation Rates
Solar panel degradation rates vary depending on the manufacturer and the type of panel. A common degradation rate for high-efficiency solar panels is around 0.3-0.5% per year, but some panels may degrade at a faster rate of 1% or more per year. This means that after 25 years, a panel with a 0.5% annual degradation rate may have lost around 12.5% of its original efficiency, while a panel with a 1% annual degradation rate may have lost around 25% of its original efficiency.
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