Civil Engineering Reference
In-Depth Information
Cox and Raghuraman (
1985
) explored several useful design features of air-
based flat-plate PV/T collectors in order to determine their effectiveness and
interaction on the basis of a computer simulation. They found that the air PV/T
types are usually less efficient than the liquid ones due to low PV cell packing
factor, low solar absorptance, high infrared emittance and low absorber to air heat
transfer coefficient. Methods to tackle these drawbacks were mainly recommended
on two major ways: increasing the solar absorptance and reducing the infrared
emittance. The results showed that when the packing factor is greater than 65 %, a
selective absorber could actually reduce the thermal efficiency when used with a
gridded-back cell. The optimum combination for an air PV/T module was sug-
gested to consist of gridded-back PV cells, a non-selective secondary absorber and
a high-transmitting/low-emissive cover above the PV cells.
Grag and Agarwal (
1995
) developed a simulation model to investigate the
effect of the design and operational parameters of a hybrid PV/T air-heating
system on its performance. It was found that whether or not to use single- and
double-glass covers in a PV/T air-heating system largely depended on its design
temperatures as the extra glass cover might lead to the increased transmission
losses, and beyond some critical point, the single-glass cover can collect more heat
than double glass does. The parametric studies showed that the system efficiency
increases with increase in collector length, mass flow rate and cell density, and
decreases with increase in duct depth for both configurations. However, as material
cost increases by increasing the number of glass covers, collector length, cell
density, duct depth and mass flow rate, final selection of design parameters and
operational variables of a PV/T system must be based on the cost-effectiveness of
the system by minimising the LCC of the system.
Kalogirou (
2001
) carried out the modelling and simulation of the performance
of a hybrid PV/T solar water system by using TRNSYS, which is a transient
simulation program with typical meteorological year (TMY) conditions for Nic-
osia, Cyprus. The PV system consisted of a series of PV panels, a battery bank and
an inverter, whereas the thermal system consisted of a hot water storage cylinder, a
pump and a differential thermostat. The results showed that the hybrid system
increases the mean annual efficiency of the PV solar water system from 2.8 to
22.7 % and in addition covers 49 % of the hot water needs in a house, thus
increasing the mean annual efficiency to 31.7 %. The life cycle savings of the
system were calculated at Cy£790.00, and the payback time was 4.6 years.
Tonui and Tripanagnostopoulos (
2008
) constructed an air-based PV/T solar
collector which applied two low-cost approaches to enhance heat transfer between
the air flow and PV surface. A finned metal sheet was attained to the back wall of
the air channel to improve heat extraction from the PV modules. The experimental
tests were carried out on the air-based PV/T system which used a 46-Wp-rated
commercial pc-Si PV module and has 0.4 m
2
of aperture area as the absorber plate.
The results showed good agreement between predicted values and measured data.
It is found that the induced mass flow rate and thermal efficiency decrease with
increasing ambient (inlet) temperature and increase with increasing tilt angle for a
given insulation level. The results also showed that the optimum channel depth
