Civil Engineering Reference
In-Depth Information
ciency of
the solar cell before the lamination process, after the lamination and under stress. In
addition, through the use of contact extensometers placed on the ETFE foils and the
solar cell, it has been possible to measure the elongation under loading and the load
transfer mechanism between the two layers in
Therefore, the test campaign was planned in order to investigate the ef
uenced by the encapsulant. Finally,
the de-lamination of the encapsulant has been investigated under stress up to
rupture of the sample determining the corresponding critical tension load.
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5.2.1 State of the Art
There are several strategies for the integration of OPV cells into ETFE cushions for
building application. The most promising approach is based on the direct printing of
OPV cells onto ETFE foils, however this technique is characterised by huge dif-
ciency over large areas.
For this reason, the most accessible way is the mechanical integration of
ficulties related to the ETFE substrate and the modules
'
ef
exible
solar cells, already commercialised for other applications but generally based on
PET substrates that are inadequate for membrane structures. Therefore, the OPV
modules could be located in a pocket made from two ETFE layers welded together
at their edges. Despite the poor aesthetical quality of the final result, the advantage
of this method is that the modules would not be subjected to stresses from the
structure.
The lamination process could be a valid alternative and a considerable
improvement to the standard mechanical integration. The commercial OPV mod-
ules based on PET substrates can be integrated into ETFE foils by means of an
appropriate material that is able to provide the required adhesion strength between
PET and ETFE by setting the optimal pressure and temperature parameter. The
reduced level of adhesion which characterise the ETFE smooth surface is generally
increased by means of a speci
fl
.
The mechanical properties of OPV cells integrated through lamination are
complicated by the ETFE time and temperature dependent behaviour with a
complex stress-strain relationship which can be elastic, visco-elastic and plastic
depending on the applied load (Galliot and Luchsinger
2011
).
The mechanical properties of ETFE foils are generally investigated through
uniaxial tensile tests because of their simplicity regarding the set-up, the post-
process, the shape and size of the sample, with the main limitations being the
absence of a biaxial control and the impossibility of determining the Poisson
c pre-treatment called
“
corona
”
s ratio.
In addition, if the testing activity aims to investigate the material beyond its elastic
properties, the uniaxial results become useless and a biaxial test is required in order
to examine the plasticity behaviour. For foils, the bursting test or bubble in
'
ation
test is quite widespread because of the relatively simple test rig and the possibility
to achieve a higher ultimate stress value before failure with the only limitation of a
single stress ratio (1:1). On the other hand, the biaxial extension of a cruciform or
square specimen enables the control of several parameters such as the load ratio,
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