To view this page ensure that Adobe Flash Player version 11.1.0 or greater is installed.
COMMERCIAL FEATURE
The right bill of materials
for solar modules
D uPont Photovoltaic Solutions has
of the parks were showing signs of visual
numerous types and styles of modules
established an extensive fielded
defects or changes. The size of the park
is encapsulant yellowing; typically it is a
module evaluation programme
did not appear to matter as the trend was
result of UV exposure. The encapsulant
to develop the knowledge base which
the same for both parks over 5.0 MWp
is formulated with cross-linking agents,
will enable a better understanding of
and for smaller installations that were
free radical scavengers and UV blockers
how modules and materials age and
less than 40 kWp. After totalling
to prolong the life of the module, and
degrade in the real world environment.
the visual defects, 32 MWp out of the
while the EVA can yellow on its own,
As part of this work, solar field visits have
61 MWp were found to be showing visual
these additives have also been known to
been conducted on a global scale with
signs of degradation or changes. Defects
yellow. This yellowing phenomenon has
over 60 fields inspected in the United
such as Partially Induced Degradation
been known to reduce transmission by
States, Canada, India, China, Japan,
(PID) or hot spots were not included in
5% directly impacting power.
Europe, Turkey, and the Middle East.
this survey. These degradation modes
Out of the 32 MWp of modules
These fields have ranged from newly
are well documented and have led to
with visual defects, backsheets defects
commissioned to 30 years old.
safety and performance issues.
alone accounted for 42% of all defects.
During field inspections, a Fourier
Solar parks of all ages showed signs
The backsheet is responsible for the
transform infrared spectrometer (FTIR)
of visual defects with an alarming trend of
electrical insulation and protection of the
was used to identify the chemical
these defects occurring both on a large
module. With the backsheet representing
composition of the outer layer on
scale in relatively young modules with
such a large percentage of the defects
the back of the module. This aids in
less than six years in the field. A great
observed, a very substantial risk exists
determination of the type of backsheet
deal of science and engineering go into
in terms of safety and potential for long
used by module manufacturers. The
designing and producing a module that
term power generation. The defects of
inspections focus on checking for any
will last 25 years in the environment, and
the most concern for backsheets include
visual changes in the module such as
the current qualification standards are not
cracking, yellowing, and delamination.
yellowing, issues with the backsheet
catching these early degradations.
Modules containing backsheets that
protection, snail trails, etc.
Ribbon corrosion is any change in
have cracked and delaminated represent
Across Europe, Turkey and the
colour that was noticed on the solder
actual failures of the backsheets, but an
Middle East, 22 crystalline-silicone solar
ribbons. This darkening of the ribbon
early potential predictor of backsheet
parks were surveyed with a very wide
surface can be due to darkening of
failure is also yellowing of the backsheet.
distribution of sizes from 1.4 kWp to
UV-sensitive flux residues, which would
Yellowing of the backsheet is typically
13.3 MWp for a total of about 61 MWp
only impact the aesthetics of the module.
associated with degradation of the
of installations. The parks ranged in
However, ribbon corrosion in extreme
polymer, and degradation of the polymer
age from two to 12 years. Only three
cases can lead to backsheet degradation
in severe cases can compromise the
of the installations surveyed were
by series resistive heating which will
mechanical properties. After day-
rooftop-based, the majority were ground-
eventually affect the safety and power
night thermal cycles of a mechanically
mounted on a mixture of fixed structures,
generation of the module.
compromised backsheet, cracking or
single axis trackers and double axis
Along with ribbon corrosion and snail
delamination of the backsheets can
trackers. trails, a third defect that can be found in
occur, resulting in loss of electrical
During the field
protection of the module. Tedlar
inspections, the focus was on
outer layer based backsheets
the visual aspect of the solar
had the lowest occurrence of
panels, which can be an early
these defects.
and first indicator of failure
This work reinforces
that can lead to more serious
that the best indicator of
problems. The visual changes
performance of materials is real
and defects types looked for
exposure to the environment,
during inspections included
and that many of these early
ethylene-vinyl acetate (EVA)
failures were not caught by
yellowing, ribbon corrosion,
current qualification testing.
snail trails, backsheet cracking,
Unfortunately, given the
backsheet backside yellowing
no-replacement policy of the
and backsheet front side
module makers for many of the
yellowing. A reoccurring theme
defects discussed, the best way
found during the inspections
forward is to select more proven
Percentage of defects observed by type for all the parks combined (61 MWp). materials, like Tedlar TPT. ESI
was that a sizable proportion
92 ESI AFRICA ISSUE 1 2014