Electroluminescent based functional release testing for photovoltaic installations

The proper function of photovoltaic installation was very unsecure to test right now. The only test method consisted on a statistical analysis comparison on the produced power. The uncertainty of the statistics is obvious as there is no precise data of the sun radiation available. Even if a deviation from the generated performance is seen, defects which are not showing obvious exterior damage can’t be seen.

Lion System has developed with PV-EL tester a new mobile quality assurance test tool which allows flexible outdoor functional release and final Acceptance testing on photovoltaic installations.

It is now first time that new high resolution InGaAs near infrared cameras allows functional release testing on installed photovoltaic installations with allowing a precise allocation of the defect. The applied electroluminescent imaging is a contactless image based measuring principle allowing looking directly into the cells of a photovoltaic module. The principle allows detecting defects which have a direct influence on the performance as well as on the lifetime.

Defects which are due to the module manufacturing as well as defects which are due to mechanical stress during transportation or at the installation are seen and documented. Defects which due to module aging are reducing the revenues are also seen and documented.

Electroluminescent imaging principle

By connecting the photovoltaic module to a DC voltage electrons in the cells are recombined and are emitting light. The module is shining in the near infrared spectrum a non visible area for the human eye. This is called electroluminescent imaging. The module lighting is visualized for the human eye by a high resolution near infrared InGaAs camera working in a range of 900 to 1700nm.
There is a direct relation between the photon emission of a cell and the efficiency of this area in the power generation.
The electroluminescent functional acceptance test is siutable for mono- and polycrystalline photovoltaic module as well as Si based thin film modules.

Electroluminescent image from a damaged photovoltaic module.
The cell brightness is showing the defective cell areas and varying functionality.

Defects and documentation

The final electroluminescent report gives the owner the guarantee that its new photovoltaic installation is in good conditions/shape. Defects showing an earlier degradation and by this a revenue reduction of the installation are detected and documented.

Electroluminescent imaging on already existing installations allows the detection of modules which are by damage or adding generating some revenue reduction.

A) Module measurement before installation.

Measurment of every single module at the supplier or at the installation location. Documentation of every module including identifcation number. Required is a closed room  to perform the measurement.

Measured are:

• Micro cracks, splinter, cell fractures, interrupted contact finger,
• Cell fractures showing an electrical separation with the resulting dead cell areas,
• Short circuit in the solar cell,
• Defective solder joints, 
• Defect strings or bypass diodes.

B) Module measurement after installation.

The measurement is performed on the assembled installation. The test requests a direct access to the supply line cable of the different installation strings as well as to a 380V power supply on site. The measurement can only be performed from nightfall where the installation isn’t working with a maximum angle of 25° between camera and modules. Optionally an elevator might be required for some measurement on roof installations.

Measured are: 

• Modules of different transmission power within a String
• Cell fractures caused by manufacturing or installation

If you want more information on this subject please contact us.