Electroluminescence (EL) images for quality assessment of solar modules

Electroluminescence (EL) is a technology that reveals electrical defects inside the solar module. Such defects—which cannot be detected visually—pose a risk of lower power yield, faster power degradation, and thus reduced performance of the solar system.

How does electroluminescence EL work?

During normal operation, a solar cell absorbs light and converts the radiant energy into electrical current. Electroluminescence reverses the solar cell's function. When a solar cell is connected to a power source, it begins to glow. However, the emitted radiation is invisible to the human eye because it lies in the infrared spectral range. Therefore, special cameras are required for EL imaging.

A segment of a solar cell glows brighter the better the electronic processes inside it are functioning. Dark spots indicate that the cell isn't functioning optimally. An EL image allows a view inside the solar cell. It makes visible what is invisible from the outside. EL is thus somewhat comparable to an X-ray image.

What defects can be seen in EL images?

EL radiation emanates from the individual solar cells, meaning defects in the cell itself, as well as some defects in the wafer, can be identified. Furthermore, defects during module production can also be detected. EL, for example, is very helpful for assessing the electrical contact between solar cells, since poor soldering prevents current from being transported away from the affected area of the solar cell. Breaks in the solar cell are most clearly visible.

Tip #1 - SOLYCO stands for full transparency regarding product quality and provides EL images for 100% of the PV modules delivered upon request. Ask other suppliers about their policies before choosing a product.

Tip #2 - Producing quality costs money. Of course, if you buy the cheapest product, you can't expect to get the highest quality. SOLYCO stands for the highest quality and an excellent price-performance ratio.

Is an EL image an important quality feature?

An EL image is a very powerful tool for assessing the overall quality of a solar module, as it can detect serious defects in the wafer, solar cell, and module areas. However, the correct analysis of an EL image requires in-depth technical expertise, and not all darker areas are necessarily due to defects.

Are there classifications of PV modules with regard to EL?

All modern factories conduct EL analyses as part of their quality assurance. In large-scale solar power plant projects, it's common for solar modules to be classified not only by electrical output but also by EL. However, this is unusual in the rooftop market. Many suppliers use this to supply their "B-grade" EL solar modules, which would not be accepted by professional buyers, to this market segment.

What are the risks associated with poor EL images?

Certain EL anomalies can be attributed to defects in the wafer material or errors in the cell manufacturing process. This can, for example, be associated with poor low-light performance, resulting in lower power production. Obvious defects in soldering quality can lead to increasing electrical resistance values during temperature fluctuations, resulting in an unusually rapid power loss, which also reduces power production. In general, PV modules with poor EL characterization carry a higher risk of underperformance.