Bi-fluid Photovoltaic/Thermal PV/T Solar Collector with Three Modes of Operation: Experimental Validation of a Theoretical Model

  • Hasila JarimiEmail author
  • Mohd Nazari Abu Bakar
  • Mahmod Othman
  • Mahadzir Din
Conference paper


This chapter discusses theoretical and indoor experimental studies of a bi-fluid type photovoltaic/thermal (PV/T) solar collector. Two-dimensional steady-state analysis was developed and computer simulations were performed using MATLAB. Experiments were conducted for steady-state analysis under the solar simulator at Solar Energy Research Lab UiTM, Perlis, Malaysia, and under real sky conditions of Northern Peninsular Malaysia, to validate the model. The solar collector and the test rig facilities were fabricated to be suitable for mathematical validation purposes in both indoor and outdoor testing. For indoor collector testing, at an average wind speed of 1 m/s and average solar radiation of 700 W/m2, the air and water mass flow rate was varied from 0.0074 to 0.09 kg/s and 0.0017 to 0.0265 kg/s respectively. The thermal efficiency increased as the mass flow rate increased. At a mass flow rate of 0.0262 and 0.0066 kg/s for air and water respectively, the thermal efficiency curves tended to plateau, which marked the optimum point of the fluid flow. For the simultaneous mode of fluid operation, testing was conducted with air and water fixed at a flow rate of 0.0262 and 0.0066 kg/s respectively, while the fluids’ mass flow rate was varied according to the range used during the independent mode. The range of the computed efficiencies for the simultaneous mode were higher than for the independent mode. In this study, collector outdoor testing was conducted for each mode of operation on a typical day in January in Perlis, Northern Peninsular Malaysia. Based on the outdoor monitoring analysis for simultaneous mode, the performance of the collector was also higher overall than the independent mode. The test was conducted by monitoring the performance of the collector with the air mass flow rate and water mass flow rate fixed at 0.0262 and 0.0066 kg/s respectively. Theoretical analysis was also performed and then validated against the experimental results by a direct comparison of the plotted curves and using mean absolute percentage error (MAPE) analysis. For the air, water and simultaneous modes, by taking into account both indoor and outdoor collector testing, the theoretical and experimental curves were found to be in good agreement, and the computed MAPE values for the fluids’ output temperature were less than 2 %. Thus, the two-dimensional mathematical model was proven valid. The PV/T collector designed in this study has a variety of applications because it can be operated in three different modes of fluid operation, and the theoretical model is useful in modelling all three modes without further modification.


Photovoltaic/thermal 2D analysis Bi-fluid Indoor Outdoor 



Collector aperture area’s subsegment, which is equal to the area of the PV module’s subsegment (m2)


Conversion power factor


Specific heat capacity of air


Specific heat capacity of water


Inner pipe diameter


Outer pipe diameter


A General subscript to represent a fluid


A Friction factor in a fluid’s channel


Global radiation


Heat transfer coefficient (W/m2 K)

hcvbs f1

Convection heat transfer coefficient from back surface of Tedlar to air flow (W/m2 K)

hcvbs f2

Convection heat transfer coefficient from back surface of Tedlar to water flow (W/m2 K)

hcvfin f1

Convection heat transfer coefficient from surface of a fin to flowing air (W/m2 K)


Wind convection heat transfer coefficient (W/m2 K)


Generalised notation for heat transfer coefficient of linear equations derived from developed energy balance equations for general heat transfer coefficient i (W/m2 K)


Radiation heat transfer coefficient between inner surfaces of collector (W/m2 K)


Radiation heat transfer coefficient from PV cells to sky (W/m2 K)


Thermal conductivity of fin (W/mK)


Thermal conductivity of air (W/mK)


Thermal conductivity of water (W/mK)


Thermal conductivity of photovoltaic cells (W/mK)


Length of fin (m)


Subsegment for each temperature node

\( {\overset{.}{m}}_{f1} \)

Air mass flow rate (kg/s)

\( {\overset{.}{m}}_{f2} \)

Water mass flow rate (kg/s)


Total number of fins


Rate of heat flux (W/m2)

quf1, m

Rate of heat transfer per unit area for air nodes (W/m)

quf2, m

Rate of heat transfer per unit area for air nodes (W/m)


Reynolds number


Total rate of solar energy absorbed by solar cells of PV module


Total energy absorbed by Tedlar


Temperature (K)


Ambient temperature (K)

Tbp, m

Temperature nodes of surface of back plate (K)

Tbs, m

Temperature nodes of rear surface of Tedlar (K)


Mean temperature of surface of back plate with fins (K)


Mean temperature of rear surface of Tedlar (K)


Mean temperature of cell (K)

Tf1, m

Temperature nodes of air flow in channel (K)

Tf2, m

Temperature nodes of water flow in copper pipe (K)

Tfin, m

Mean temperature of fin at subsegment m (K)

TPV, m

Temperature nodes of PV cells (at centre of cells) (K)


Temperature at reference point


Sky temperature (K)


Mean inner wall temperature of copper pipe (K)

Ut, m

Overall top heat loss coefficient for subsegment m


Maximum velocity of air (m/s)


Wind speed (m/s)


Tube spacing (m)


Absorptance of PV cells


PV module packing factor


Temperature coefficient at reference temperature


Thickness of PV module


Thickness of Si cells


Thickness of Tedlar layer


Fin thickness


Area of subsegment of PV module


Distance between temperature nodes (\( \Delta x=1\ \mathrm{cm} \))


Emissivity of sky


Emissivity of glass cover

γbsbp, m

Area correction factor for heat transfer from back surface of Tedlar to surface of back plate with fins

γbs f1, m

Area correction factor for heat transfer from back surface of Tedlar to flowing air

γbs f2, m

Area correction factor for heat transfer from back surface of Tedlar to flowing water

γfin f1, m

Area correction factor for heat transfer from fin surfaces to flowing air

γbp f1, m

Area correction factor for heat transfer from surface of back plate with fins to flowing air

γbpa, m

Area correction factor for heat transfer from surface of back plate with fins to ambient


Transmittance factor of front cover glass of PV module


Transmittance factor due to double glazing (glass covers)




Electrical efficiency of a PV cell


Electrical efficiency


Electrical efficiency converted to equivalent thermal efficiency


Fin efficiency


Fin effectiveness


Electrical efficiency at reference temperature

ηth f1

Thermal efficiency of air

ηth f2

Thermal efficiency of water

\( \sum {\eta}_{\mathrm{th}} \)

Total thermal efficiency of solar collector

\( \sum {\eta}_{\mathrm{PVT}} \)

Primary energy saving or equivalent thermal efficiency

\( \sum {\eta}_{\mathrm{th},\mathrm{inst}} \)

Instantaneous total thermal efficiency of solar collector



This work was funded by the Malaysian Fundamental Research Group (FRGS) 600-RMI/ST/FRGS 5/3/Fst (160/2010) and Solar Energy Research Lab, Universiti Teknologi Mara (UiTM), Perlis, Malaysia


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Authors and Affiliations

  • Hasila Jarimi
    • 1
    Email author
  • Mohd Nazari Abu Bakar
    • 1
  • Mahmod Othman
    • 1
  • Mahadzir Din
    • 1
  1. 1.Universiti Teknologi Mara PerlisPerlisMalaysia

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