Civil Engineering Reference
In-Depth Information
To increase the PV electrical efficiency and make good use of the incident solar
radiation, it is most desired to remove the accumulated heat from the concealed PV
surface and use this part of heat appropriately. The PV/T is a technology devel-
oped for this purpose, which combines the PV cells/modules and heat extraction
components into a single module. This allows cooling of the PV cells leading to
increased PVs' electrical efficiency and, in the meantime, simultaneously utilizing
the extracted heat for heating purpose. By doing so, the PV/T solar collector can
obtain the enhanced overall solar efficiency and thus provide a better way utilizing
solar energy. The PV/T, merging PVs into the solar thermal module, represents a
new direction for renewable heating and power generation. Figure
2
indicates the
interrelationship among different solar conversion technologies.
A typical PV/T module is a sandwiched structure comprising several layers,
namely from the top to bottom, a flat-plate thermally clear covering as the top
layer; a layer of photovoltaic cells or a commercial PV lamination laid beneath the
cover with a small air gap; tubes or flowing channels through the absorber and
closely adhered to the PV cell layer; a thermally insulated layer located right
below the flow channels. All the layers are fixed into a framed module using the
adequate clamps and connections. Figure
3
is a schematic of a typical PV/T
module structure.
The general concept of PV/T technology was originally addressed by Kern and
Russell (
1978
). For a PV/T module, the solar irradiation with the wavelength from
0.6 to 0.7 lm is absorbed by the PV cells and converted into electricity, while the
remaining irradiation is mostly transformed in the form of thermal energy. The
PV/T module can collect solar energy at different grades (wavelengths) and
consequently lead to an enhanced energy and exergy efficiency. According to
Zongdag et al. (
1999
) and Zhao et al. (
2011
), the PV/T module could collect and
convert higher percentage of solar energy than either an individual PV panel or
thermal collector do at the same absorbing area and therefore offers a potential
creating a low-cost and highly effective solution for heat and power generation.
A PV/T module is basically derived from the combined functions of a flat-plate
solar (thermal) collector and of a photovoltaic panel. The overall efficiency is sum
of the collector's thermal efficiency g
th
and the PVs' electrical efficiency g
e
, which
are defined as the ratios of useful system heat gain and electricity gain to the
incident solar irradiation striking on the collector's absorbing surface, and is
written as follows:
Fig. 2 Network of different
solar conversion technologies
(Zhang et al.
2012
)
