Solar modules degrade over time through several mechanisms: light-induced degradation (LID) in the first hours of exposure, potential-induced degradation (PID) from voltage stress, thermal cycling that stresses materials as they heat and cool, humidity and moisture ingress that corrodes internal components, ultraviolet exposure that ages the encapsulant and backsheet, and microcracks in cells from handling, transport or mechanical load. Together these cause a small annual loss of output, typically a fraction of a percent per year after an initial first-year drop. Choosing quality modules with good encapsulants and certification, and handling and installing them carefully, slows degradation and protects long-term output.
”- Modules degrade through several mechanisms, not one, each causing small output losses.
- Key causes: light-induced (LID) and potential-induced (PID) degradation, thermal cycling, humidity, UV, and microcracks.
- Typical degradation is a fraction of a percent per year after a larger first-year drop.
- Quality encapsulants, good certification and careful handling slow degradation.
- Lower-degradation modules produce meaningfully more energy late in a 25-to-30-year life.
Degradation is normal, but the rate varies
Every solar module loses a little output as it ages. That is expected, and manufacturers publish a degradation curve and a performance warranty around it. What varies, and what matters, is the rate. A module that degrades slowly is still producing most of its original output decades later, while a fast-degrading one falls off sooner. Understanding the causes helps you buy slow-degrading modules and avoid accelerating the process.
Light and voltage: LID and PID
Light-induced degradation (LID) happens in the first hours of sun exposure, causing a small initial drop as the cell stabilises. Potential-induced degradation (PID) is caused by voltage stress between the cells and the frame over time, and can be significant in poorly built modules or badly designed systems. Quality modules are engineered to resist PID, which is one reason certification and build quality matter.
Heat, humidity and UV
Modules heat up in the sun and cool at night, and this thermal cycling repeatedly stresses the materials and solder joints. Humidity and moisture that find their way past the seals corrode internal components and connections. Ultraviolet light gradually ages the encapsulant and backsheet, the polymer layers that protect the cells. The encapsulant quality, in particular, has a large influence on how well a module resists moisture and UV over decades.
Microcracks and mechanical stress
Cells are thin and brittle, and rough handling, poor packing, transport shocks or heavy snow and wind loads can create microcracks. These tiny fractures may not be visible but can grow over time and reduce output. Careful handling during transport and installation, and modules built to withstand mechanical load, limit this. This is one reason buying from suppliers with proper packing and handling matters as much as the module spec itself.
How to limit degradation
You cannot stop degradation, but you can slow it. Choose modules with strong certification, good PID resistance and quality encapsulants, and check the published degradation rate and performance warranty. Handle and install carefully to avoid microcracks. Over a 25-to-30-year life, a module that degrades a little more slowly each year ends up producing meaningfully more total energy, so a lower degradation rate is worth paying attention to at purchase.
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