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the hybrid air collector with glass-to-glass PV module has an approximately 2% higher
overall thermal efficiency than the PV module with glass-to-tedlar.
Dubey et al. (2009) presented an analytical expression for electrical efficiency of
PV/T hybrid air collector. They tested four different configurations of photovoltaic
modules which are: glass-to-glass PV module with duct, glass-to-glass PV module
without, glass-to-tedlar PV module with duct, and glass-to-tedlar PV module without
duct. For electrical efficiency, the results show that the differences between PV modules
with glass-to-glass and PV modules with glass-to-tedlar with and without duct are
1.24% and 0.086% respectively; the difference between the electrical efficiency of PV
modules with glass-to-glass with and without duct is 0.66%. Similar to Dubey et al.'s
work, Dupeyrat et al. (2011) had also worked to improve the PV module optical
properties specifically to suit for hybrid PV/T collector application. It was shown that
“the design of a PV module for a PV-T collector allows the use of alternative materials
for the encapsulation process and a new encapsulation setup has been developed. This
is a combination of a front layer with a low refractive index instead of glass cover and a
low UV absorbing layer instead of the conventional EVA material.'' The results showed
that the said configuration of the PV/T encapsulation module increased the generated
current density at least 2 mA/cm 2 . Compared to equivalent mc-Si cells laminated as
a conventional standard glass/EVA/mc-Si/EVA/Tedlar module, the PV/T encapsulation
module also has higher solar absorption coefficient. They designed, built and tested a
prototype of PV/T collector based on experiments, and the results show 79% thermal
efficiency and 8.7% electrical efficiency, which is 87% total efficiency.
Low cost performance improvements of PV/T solar collectors for natural air flow
operation were introduced by Tonui and Tripanagnostopoulos (2007) and Tonui and
Tripanagnostopoulos (2008). Two low-cost modifications of heat extraction were
investigated in PV/T air system channel to cool down the PV as well as increase the
thermal yield. They suggested using either finned back wall or thin flat metal sheet
suspended at the middle of an air channel in the PV/T air configuration. The system
consists of the PV module with a simple air channel attached on the back. It is very
similar to using the PV module as an absorber plate with conventional air collectors.
For the improved systems, the channels are modified by attaching a rectangular pro-
file fins on the other side of the wall to the PV rear surface or by suspending a thin
flat aluminum metal sheet in the middle of the air channel (Arif Hasan and Sumathy,
2010). Compared to attaching fins to the PV rear surface, attaching fins at the back
wall was relatively easier, because attaching fins at the back of the PV module requires
special designated features during the PV modules production. They pointed out that
since the fins and metal sheets are easily obtained from the existing material which
is not expensive, and the fabrication and modification are not complicated, being
incorporated in the middle or on the opposite wall of the air channel, the total cost
of the design models for the PV/T sir collectors is low. They also modified the duct
geometry by changing the hydraulic diameter of the duct. The test results show that,
when the hydraulic diameter of the duct is decreasing, the heat transfer surface area
in the channel and convection heat transfer coefficient increased, thus more heat can
be transferred from the PV panel to the air stream. Both the PV cooling capability
and thermal efficiency of the system is increased. Tripanagnostopoulos et al. (2000)
have also presented low cost improvements in integrated air cooled hybrid PV thermal
systems specifically for buildings. They noted that the heat exchanging surface area
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