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Protecting solar cells from UV light
Scientists in France tested the effectiveness of various encapsulant
materials, used to laminate solar cells into modules, at protecting
cells and other components from damage caused by ultraviolet (UV)
light. Their findings show that encapsulants with additives
specifically designed to absorb UV light tend to turn yellow over
time, which can contribute to various other problems with performance.
By
MARK HUTCHINS
22June 2023
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Image: dimitrisvetsikas1969, Pixabay
Lamination and encapsulant materials play a key role in protecting PV
modules’ inner workings from heat, cold, dust, damp and, somewhat
ironically, from the light they are built to absorb. Ultraviolet light
is a factor in several types of degradation and performance loss
observed in the field, and is likely
still a problem with the latest cell technologies.
For the encapsulant
material itself, yellowing over long periods of exposure to light
is a common problem that can cause performance loss by itself, and
also reduce the level of protection against other degradation. And
this was the focus of a group of scientists led by France's National
Solar Energy Institute (INES), a division of the French
Alternative Energies and Atomic Energy Commission (CEA), who
conducted accelerated testing on modules built with a range of
different encapsulation materials.
The group fabricated single-cell modules, using heterojunction solar
cells laminated at 160 degrees with five different commercially
available PV encapsulant materials – two based on ethylene vinyl
acetate (EVA) and three based on polyolefins (POE). These modules were
illuminated for 4,200 h, and samples were also tested for up to 1,300
h under ultraviolet radiation and an elevated temperature, to test the
effects of UV light alone.
The experiments are described in full in the paper “Solar
cell UV-induced degradation or module discolouration: Between the
devil and the deep yellow,” published in Progress
in Photovoltaics. After testing, the modules were inspected
visually and measured for fluorescence and current/voltage
performance.
Results showed that the EVA encapsulant was most affected, and two of
the POE samples also exhibited minor yellowing. Notably, the three
samples that did have yellowing were those that contained additives
designed to absorb UV light. After 4,200 h of testing, the EVA module
was shown to have lost 4.2% of its initial performance.
The study concludes that UV-absorbing additives tend to degrade,
affecting PV module performance over time. However, the researchers
note that the protection they provide against other degradation
mechanisms would likely still justify their use – as long as the solar
cells they are protecting remain vulnerable to UV-induced degradation.
“The destruction of UV absorbers is an issue affecting the integrity
of the whole PV module and can lead to accelerated delamination, among
other critical types of damage,” the researchers explain. “There is
then a challenge to find new ways to bolster the photoprotection of
the device, especially for the most stringent environments, such as
those located in deserts.”
As for solutions to this challenge, they suggest trialing
mineral-based rather than organic UV absorber materials, and also note
that quantum dots may eventually become an alternate solution, though
this is still in earlier stages of research. Finally, they suggest
investigating UV-absorbing glass, replacing the need for encapsulant
additives.
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