9 Solar Module Technology
237
the formation of bubbles and voids and to prevent the misalignment of the cells.
The real curing (i.e. the polymer cross-linking) of the encapsulant generally takes
place at temperatures between 130 and 160 °C, during a few minutes. The membrane is then removed and the lamination chamber vented, by letting air enter the
chamber. An optional cooling step can be applied to attenuate mechanical stress
that may arise due to the mismatch in the thermal expansions coefficients of
the different components of the module. Thereby the durability properties (and
for some polymers the optical transmittance, too) of the module are improved.
Overall, the lamination process can take between 10 and 20 min. Given the relatively high operating temperatures of the heating plate (145–160°), the energy
consumption of the process can be significant. The quality of the lamination step
is critical in ensuring long-term performance and durability of the modules. The
lamination process parameters (temperature, pressure, time and heating ramps)
need to be carefully optimized and tailored to the polymer used. On the other
hand, the most critical quality parameter for a laminator is having a homogeneous
heat distribution over the heating plate. In a high-quality laminator, temperature
homogeneity fluctuations should be constrained to ±2% at most. An uneven
temperature distribution may lead to different levels of cross-linking of the EVA,
which, in the long-term, could lead to lack of adhesion and delamination in parts
of the module.
5. Finishing: after the lamination, polymer material in excess is removed from
the edges (trimming), an anodized aluminium frame is applied to the edges of
framed modules (framing), and the electrical terminations of the modules are
soldered to a junction box. Modules in a glass/foil structure are usually framed.
Glass/glass modules, which generally have a superior mechanical stability, can
be manufactured unframed.
6. Quality inspection: in-line routine quality checks generally include power measurements at STC (1000 W/m
2 , 25 °C), low-irradiance performance (200 W/m
2 ,
optional), and electro-luminescence (EL) imaging.
9.3 Module Testing, Reliability and Lifetime
9.3.1 Electrical Performance
In a similar way as for individual solar cells, the performance of modules is characterized by the short-circuit current I sc , by the open-circuit voltage V oc , by the
current at maximum power point (MPP) I mpp , by the voltage at MPP V mpp , by the
Fill Factor FF, by the power P max , and by the efficiency η measured at Standard Test
Conditions (STC = 1000 W/m
2 , AM1.5, 25 °C). As modules are sold in terms of
e/W p (or $/W p ), a correct STC (i.e. W p Watt-peak) characterization of the module
power (power rating) is critical, as it can be affected by several errors and measurement artifacts. These include spectral mismatch errors (deviations from the reference
237
the formation of bubbles and voids and to prevent the misalignment of the cells.
The real curing (i.e. the polymer cross-linking) of the encapsulant generally takes
place at temperatures between 130 and 160 °C, during a few minutes. The membrane is then removed and the lamination chamber vented, by letting air enter the
chamber. An optional cooling step can be applied to attenuate mechanical stress
that may arise due to the mismatch in the thermal expansions coefficients of
the different components of the module. Thereby the durability properties (and
for some polymers the optical transmittance, too) of the module are improved.
Overall, the lamination process can take between 10 and 20 min. Given the relatively high operating temperatures of the heating plate (145–160°), the energy
consumption of the process can be significant. The quality of the lamination step
is critical in ensuring long-term performance and durability of the modules. The
lamination process parameters (temperature, pressure, time and heating ramps)
need to be carefully optimized and tailored to the polymer used. On the other
hand, the most critical quality parameter for a laminator is having a homogeneous
heat distribution over the heating plate. In a high-quality laminator, temperature
homogeneity fluctuations should be constrained to ±2% at most. An uneven
temperature distribution may lead to different levels of cross-linking of the EVA,
which, in the long-term, could lead to lack of adhesion and delamination in parts
of the module.
5. Finishing: after the lamination, polymer material in excess is removed from
the edges (trimming), an anodized aluminium frame is applied to the edges of
framed modules (framing), and the electrical terminations of the modules are
soldered to a junction box. Modules in a glass/foil structure are usually framed.
Glass/glass modules, which generally have a superior mechanical stability, can
be manufactured unframed.
6. Quality inspection: in-line routine quality checks generally include power measurements at STC (1000 W/m
2 , 25 °C), low-irradiance performance (200 W/m
2 ,
optional), and electro-luminescence (EL) imaging.
9.3 Module Testing, Reliability and Lifetime
9.3.1 Electrical Performance
In a similar way as for individual solar cells, the performance of modules is characterized by the short-circuit current I sc , by the open-circuit voltage V oc , by the
current at maximum power point (MPP) I mpp , by the voltage at MPP V mpp , by the
Fill Factor FF, by the power P max , and by the efficiency η measured at Standard Test
Conditions (STC = 1000 W/m
2 , AM1.5, 25 °C). As modules are sold in terms of
e/W p (or $/W p ), a correct STC (i.e. W p Watt-peak) characterization of the module
power (power rating) is critical, as it can be affected by several errors and measurement artifacts. These include spectral mismatch errors (deviations from the reference