The degradation rate describes the natural, age-related loss of performance in photovoltaic modules over the course of their operating life. In short, it refers to the percentage by which the maximum efficiency and power output of a solar cell decreases each year due to environmental influences and material aging.
In a nutshell: Solar modules lose a minimal amount of power over the years – this is a normal physical process. A low degradation rate is the most critical quality feature for durable PV modules, as it guarantees that the system will still deliver close to its full capacity even after 25 years.
Why do solar modules age?
Solar modules are exposed to extreme conditions on roofs or open spaces for decades: intense UV radiation, severe temperature fluctuations between summer and winter, moisture, and mechanical loads from wind and snow. These factors lead to tiny chemical and physical changes within the silicon cells and the encapsulation films.
A distinction is made between initial degradation (LID – Light-Induced Degradation), which occurs in the very first hours of operation and usually amounts to 1% to 2%, and subsequent linear aging over the following decades. High-quality, modern modules currently feature an annual degradation rate well below 0.5%.
Significance of the performance warranty at a glance
Since degradation directly impacts the long-term economic efficiency and payback period of a project, reputable manufacturers offer clear warranty promises:
- Linear Performance Warranty: Instead of a rigid tiered warranty, a linear warranty ensures that the modules will not lose more than an exactly defined fraction (e.g., 0.4%) of their output per year.
- Long-Term Performance: Premium modules often guarantee a nominal output of 85% to over 89% of their original value even after 25 or 30 years.
- Planning Reliability: For commercial PV projects and B2B calculations, an extremely low, dependable degradation rate forms the foundation for precisely forecasting profitability and electricity yield over decades.
Technological differences in degradation
The choice of cell technology massively influences the degradation rate. Modern N-type cells (such as TopCon or HJT) are virtually immune to certain aging effects like light-induced degradation (LID) compared to older P-type cells. In addition, robust glass-glass construction optimally protects the sensitive cells from moisture ingress and mechanical stress (microcracks). Sourcing future-proof N-type technology minimizes the degradation rate and safeguards maximum economic yield over the entire lifecycle.