LED solar simulators for precise module testing

Whether a solar cell or solar module achieves the expected performance is not determined only once it is installed on a roof or in a solar farm. The components are measured under standardised conditions as early as the development and production stages. This is the only way to reliably determine efficiency, performance data and potential defects.

For many years, xenon light sources dominated testing technology. However, another technology is now increasingly gaining ground. At Intersolar Europe, Wavelabs demonstrated how LED-based solar simulators enable more precise and, at the same time, more cost-effective measurement of solar cells and solar modules. This approach is aimed at both research institutions and manufacturers who place high demands on measurement accuracy and reproducibility.

Wavelabs relies on LED technology for solar simulators

The company has been developing LED-based solar simulators since 2011. Unlike traditional xenon systems, the light spectrum can be flexibly adjusted. This allows the lighting conditions to be matched particularly precisely to the natural solar spectrum. A further advantage is the reduced maintenance required. LED light sources have a long service life and require significantly less maintenance than conventional systems. For laboratories and production facilities, this means lower operating costs and greater availability of the measurement systems. In the research sector in particular, the stability of measurement conditions also plays a crucial role. Only when identical test conditions can be consistently reproduced is it possible to reliably compare new cell technologies or optimise production processes.

More than 20 LEDs produce a spectrum similar to that of sunlight

At the heart of the solar simulator is a light source comprising more than 20 different LED wavelengths. Their combined effect produces a spectrum that closely resembles sunlight and illuminates the test sample evenly. Under these standardised conditions, the electrical output of a solar module or solar cell is then determined. The measured values form the basis for the technical performance specifications that are later stated on each solar module. Typical areas of application include:

• Power measurement of solar cells
• Testing of complete solar modules
• Research and development of new cell technologies
• Quality assurance in mass production
• Calibration under standardised test conditions

Electroluminescence detects defects in solar modules

In addition to conventional power measurement, modern testing systems incorporate further analytical methods. One example is electroluminescence testing, which is also an integral part of the system shown. In this process, solar cells are electrically excited and imaged using a specialised camera. The images reveal fine cracks, micro-damage or other material defects that often remain invisible to the naked eye. Such defects can impair a module’s efficiency or lead to long-term losses in power output. Combining different testing methods within a single system shortens the testing process. Power measurement, spectral analysis and defect detection can be carried out immediately one after the other, without the module having to be moved between different systems.

Integrated spectrometers monitor every measurement

A key feature of the systems presented is the continuous monitoring of the light spectrum produced. This is achieved using integrated spectrometers, which check during the measurement whether the illumination actually complies with the specified standard conditions. This additional monitoring enhances the traceability of the results. Users do not have to rely on the light source operating consistently over time; instead, they benefit from continuous monitoring of the spectral characteristics. Research institutions and the development departments of international module manufacturers, in particular, attach great importance to this form of quality assurance. In these settings, measurements often need to remain comparable over long periods in order to reliably evaluate changes in materials or processes.

LED solar simulators are gaining in importance in research and production

The transition from xenon to LED technologies is taking place gradually. The market for high-precision solar simulators is still comparatively small and limited to specialist suppliers. At the same time, interest is growing in systems that combine high measurement accuracy with low maintenance requirements. As the efficiency of modern solar cells increases, so too do the demands placed on measurement technology. Even minor differences in efficiency must be reliably detected. Added to this is the desire of many manufacturers to combine several test procedures within a single system and to automate test sequences to a greater extent. The technology presented at Intersolar Europe demonstrates how quality control in the photovoltaics sector is evolving. It is not the light source alone that determines the validity of a measurement. Only the combination of spectrally precise illumination, integrated spectral control, electrical power analysis and defect detection enables a comprehensive evaluation of modern solar cells and solar modules.