Degradation of solar modules: causes and effects

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Degradation of solar cells (international term potential induced degradation or PID) refers to the reduction in electricity generation due to physical changes in the structure of the panel itself.

Degradation of solar cells (international term potential induced degradation or PID) refers to the reduction in electricity generation due to physical changes in the structure of the panel itself. As a result of some phenomena, parasitic connections are formed between the semiconductor cells and the protective case, lamination or glass protection. Leakage currents flow through them, reducing the efficiency of the solar system.

All existing structures degrade - polycrystalline, monocrystalline, film. The question is how quickly it happens. Research shows:

·         For high-quality solar panels, PID is 2-3% of their initial performance in the first year and about 0.7% in subsequent years of operation.

·         Degradation of low-quality solar modules, and this is almost the entire cheap segment, is unpredictable and can reach 20% in the first year. Such figures cancel out any savings at the purchase stage - all calculations of the payback of a solar power plant turn out to be incorrect.

Therefore, the selection of high-quality solar panels with minimal and clearly regulated temporary degradation is the most important point at the design stage.

Degradation of solar panels occurs both due to improper operation and under the influence of some external factors

1. The structure of the modules.

According to recent studies, sodium is the main element causing increased degradation of solar modules. It is likely that other active metals are also catalysts for the process. Therefore, special attention is paid to the choice:

·         front glass - quartz glass does not contain sodium compounds and prevents degradation;

·         encapsulating material - EVA vinyl acetate film suppresses polarization, and acetic acid in its composition reduces the negative effects of glass corrosion;

·         diffusion barrier between glass and electrically active zones of a semiconductor - silicon dioxide perfectly insulates leakage currents.

Anti-reflective coatings increase the capture of solar radiation and increase electricity production. But if sodium is present in their composition, such a "helper" contributes to degradation.

2. Circuitry of the entire system

The input voltage is critical, or rather its sign relative to ground. Such degradation “is treated by the correct choice of equipment and its connection scheme.

3. Influence of the environment

Multiple experiments have shown that PID increases with:

·         an increase in humidity and / or temperature;

·         sharp temperature changes;

·         frequently repeated freeze-thaw cycles.

External factors increase parasitic currents and often lead to irreversible consequences.

Regular measurements of the open circuit voltage of each module help detect solar panel degradation in time. If access to the object is limited, electroluminescence can be used.

Timely diagnostics allows you to neutralize the causes of PID and their consequences in time, as well as restore the normal operation of the system using special measures.