Basics of the photovoltaic thermal module - Solar Energy Sciences and Engineering Applications - page 165

of the air channel is increased by attaching fins of about 15 cm on to the opposite air
channel surface. To form fin plate elements, they applied the 1.5 cm aluminum and
4cm of π profile respectively.
5.5 CONCLUSION
The feasibility of the PV/T system will be dependent upon its technical and economic
competitiveness with respect to other alternatives. The technical feasibility can be
evaluated by comparing the electrical module efficiency and thermodynamic efficiency
of such systems with those of the conventional ones, while the economic feasibility
(energy metric analysis) can be tested by balancing the capital cost of the solar system
against the savings in conventional fuel costs. As the economic feasibility is heavily
dependent on the financial parameters based on some assumptions (e.g. the inflation
rate of conventional fuel costs), it is certain that the viability of such solar systems
will be more pronounced when the environmental costs of conventional electricity
production are factored in.
As referred to in earlier sections, several studies (both theoretical and experimental)
shows that most of the systems could only achieve a maximum thermal efficiency of
about 60% for air-cooled and a slightly higher for water-cooled PV/T systems. The
reduction in thermal efficiency might be due to reflection losses (since PV surfaces are
not spectrally selective), and also due to the fact that the heat resistance between the
absorbing surface and the heat transfer medium is increased because of the additional
layers of material (e.g. tedlar). Hence, it is necessary to keep all layers between the
PV panel and the absorber as thin as possible. It should be pointed out that several
researchers (Tiwari and Sodha, 2007; Dubey et al., 2009) have confirmed to use glass
instead of tedlar, as tedlar becomes a barrier for extracting thermal energy, in turn
reducing both the electrical and overall efficiency of the system.
Poor thermal contact was also reported to be a problem by Sudhakar and Sharon
(1994) who found a temperature difference of about 15 ◦ C between PV laminate and
water output temperature. Hence, the objective of future research should aim to opti-
mize the air channel geometry of the PV/T system and to simulate the PV/T collector
characteristics, and further investigate the influence of various heat transfer promoters
on the cell temperature of the PV module for different operating conditions. It is also
essential to establish an analytical expression for the electrical efficiency of the PV mod-
ule with and without air flow as a function of climatic and design parameters, which
can be derived based on a detailed energy balance of each component of the chosen
configuration. For the case of PV/T liquid collectors, though the sheet-and-tube design
performs efficiently, the channel plate constructions may provide interesting ways of
further increasing the heat transport, provided that the channels are made sufficiently
thin. For an unglazed PV/T water collector, a heat pump can be integrated to the PV/T
system, which may be a promising development for the future.
To make solar energy devices more attractive for potential applications, it is essen-
tial to develop a thermal model of integrated photovoltaic and thermal solar systems,
which could be used to analyze the overall system performance under various cli-
matic as well as design conditions. The possibility of generating electricity and heat
energy from PV/T solar collector with either forced or natural flow (using water or