In the past, sun farmers would purchase a consignment of photovoltaic modules, and then send a representative sample of these cumbersome panels to the labs for testing to ensure they functioned at the level promised by the supplier.
Today, one of the tests that could previously only be performed in a lab can be done in the field – and the tests are the most accurate yet.
The photovoltaic research group at Nelson Mandela Metropolitan University’s Centre for Energy Research (CER) – which runs one of two photovoltaic testing labs countrywide – has acquired the country’s first outdoor electroluminescence (EL) imaging camera.
It captures images of light, not visible to the naked eye, that are emitted by the photovoltaic panel. But what truly sets this particular camera apart is that it doesn’t require the darkened lab environment usually required for EL testing, thus scientists can conduct their testing on-site.
“It is the first time in South Africa that this can be done,” said NMMU physics lecturer Dr Freddie Vorster (pictured above). “The whole set up is completely mobile, and the testing is as accurate as you can get.”
How does it work? When electric current is passed through a photovoltaic module, it lights up, although this is not in the spectrum visible to human beings. The EL imaging camera takes a photograph of the light emitted by the module, clearly showing any defective areas. “It can even pick up small cracks in the module’s cells.”
The camera then downloads this image to a computer, where scientists can observe where the weak spots are.
In the past, EL tests could only measure one module at a time but, since the modules that are deployed in a solar farm are strung together, the newly-acquired equipment allows scientists to record up to 40 at a time.
The test does not form part of the three standard International Electrotechnical Commission (IEC) tests for photovoltaic modules – nor does the thermal imaging test (which detects heat patterns) that the NMMU lab carries out as a matter of course.
However, both these in-house tests add two extra layers of information to the three that are routinely conducted. The first of these is a visual inspection to ensure there is no visible short circuitry or other obvious faults. The second is current voltage characterisation, conducted in a solar simulator, in which an intense flash of simulated sunlight – similar to the flash of a camera – is aimed at the module to test if it produces the correct amount of power, and the third is high voltage insulation testing.
“The current-voltage simulator test tells us what the current and voltage characteristics are and helps us check that what is written on the back of the module is what it says it is.
“Because the light is so intense, we can only perform this test for a fraction of a second and must capture the necessary data in that brief second.”
Vorster said the camera package was developed in Germany by a spin-off company from Berlin’s Humboldt University and has won several innovation awards. The EL camera package adds to the photovoltaic module characterisation capabilities at the CER and forms part of ongoing research and development in the field of EL characterisation.
The CER’s photovoltaic testing lab was set up to provide high level training for students in a professional testing laboratory environment and, at the same time, offer a much needed specialised service to the local photovoltaic industry. The lab is currently managed by PhD student Jacqui Crozier.
“The experience and knowledge gained from this test lab feeds directly back to our photovoltaics research activities which are primarily focused on the development of novel characterisation techniques,” said Vorster.