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where g
rc
is the initial electrical efficiency at reference temperature; b
PV
is the cell
efficiency temperature coefficient; T
pv
and T
rc
are, respectively, the PV cell tem-
perature and its reference temperature.
Alternatively, in practice, the electrical efficiency (g
e
) of a PV module can be
regarded as the ratio of measured output power (P
o
) to the overall incident solar
radiation.
g
e
¼
P
o
IA
c
ð
11
Þ
The generated electrical energy can be therefore calculated by
Q
e
¼
P
o
¼
g
e
IA
c
ð
12
Þ
2.2 Classification of the PV/T Modules
PV/T modules could be structurally and functionally very different. In terms of
coolant used, the modules could be classified as air, water, refrigerant and heat
pipe fluid-based types. In terms of the physical structure applied, the modules
could be classified as flat-plate, concentrated and building integrated types. In this
chapter, the coolant-based classification was adopted and illustrated as follows.
Air-Based PV/T
An air-based PV/T module is a solar air heater with an additional PV layer lam-
inated on the top or bottom of the naturally or mechanically ventilated air chan-
nels. This PV/T type could be formulated by incorporating an air gap between the
PV modules' back surface and the building fabric (facade or tilted roof). Usually,
this type of PV/T module is designed for the end-users who have demand in hot
air, space heating, agriculture/herb drying or increased ventilation, as well as the
electricity generation. For this type of module, air could be delivered from above,
below or on both sides of the PV absorber, as shown in Fig.
5
.
Water-based PV/T
A water-based PV/T module, as previously shown in Fig.
3
, has a similar structure
as the conventional flat-plate solar collectors. The absorber is attained with
numerous PV cells that are series or parallel connected and fixed with a serpentine
or a series of parallel tubes underneath. Water is forced to flow across the tubes,
and if the water temperature remains lower, the PV cells will be cooled, thus
leading to the increased electrical efficiency. In the meantime, the passing water
will be heated by absorbing the PV heat and will be delivered to certain heat
devices to provide heating. This part of water may be consumed or alternatively
cooled in the heating services and flows back to the module to regain heat.
Compared to the air-based system, the water-based PV/T systems could achieve
