Civil Engineering Reference
In-Depth Information
regulations related to PV/T design and installation, develop the potential research
topics/directions
for
further
improvement,
and
promote
its
potential
market
exploitation throughout the world.
PV/T is a technology combining PVs and solar thermal components into a
single module to enhance the solar conversion efficiency of the system and make
economic use of the space. The dual functions of the PV/T result in a higher
overall solar conversion rate than those of sole PV and solar thermal collector. PV/
T modules are architecturally adaptable and have the potential to develop into a
range of standardised and aesthetically appealing commercial products. Its market
potential is expected to be high compared to the individual PV and solar thermal
systems due to its obvious benefits over the independent systems.
PV/T modules could have very different structures. In terms of coolants used,
currently available PV/T configurations could be classified as air, water, refrig-
erant and heat-pipe-based types. Technical performance of a PV/T system is
usually evaluated using energy and exergy efficiencies, whereas the economic
performance is measured with LCC and CPT, and the environmental benefit is
justified by EPBT and GPBT.
Air-based PV/T is one of the most commonly used PV/T technologies and has
been developed into commercial units in many engineering practices. This type of
system can achieve maximum electrical efficiency of around 8 % and thermal
efficiency of around 39 %, and its performance is largely dependent on the air flow
speed and temperature. The major problem with the air-based system lies in its
relatively poor heat-removal effectiveness owing to the low density, specific heat
capacity and thermal conductivity of the air.
Water-based PV/T is also a very popular technology and has gained growing
application in practical projects. This type of system can achieve maximum
electrical efficiency of around 9.5 % and thermal efficiency of about 50 %, and its
performance is largely dependent on water temperature and flow rate, and water
flow channels' geometrical shape and sizes. Compared to the air-based system, the
water-based system could improve the electrical efficiency of the PVs and increase
the solar thermal energy utilisation. However, the scope for improvement is lim-
ited by a few of its inherent technical difficulties, such as arising water temperature
during the operation and complex system layout.
Refrigerant-based PV/T could significantly improve the solar utilisation rate
over the air- and water-based systems and therefore has potential to replace the
former two systems in near future. The system usually operates in conjunction
with a heat pump, and its performance is largely dependent on the type and
thermal/physical properties of the refrigerant used and structural/geometrical
parameters of refrigerant flow channels. The refrigerant-based PV/T can achieve
maximum electrical efficiency of around 10 % and thermal efficiency of around
65 %. This system represents a step forward in BIPV cooling technology, but it
practicality faces several challenges, namely potential refrigerant leakage, unbal-
anced refrigerant distribution across the panel coils, as well as difficulty in pressure
maintenance over the operation duration.
