Performance analysis of PV/Trombe with water and air heating system: an experimental and theoretical study

ABSTRACT

This paper studies an improved design of a photovoltaic/Trombe wall (PV-TW) system. It was integrating a PV panel with a serpentine-shaped copper tube as the water heating component and a single pass air channel as the air heating component. In addition to the electricity generated this type of PV-TW system enables to supply both hot air and water, which is increasing the total efficiency per unit area compared to the classical Trombe wall. The use of both fluids (bi-fluid) also creates a more excellent range of thermal applications and offers options in which hot air and water can be utilized depending on the energy needs and demands.

In this paper, the design concept of the bi-fluid PV-TW system is emphasized with 1D steady-state energy balance equations for the bi-fluid configuration are developed, validated and used to predict the performance of the bi-fluid PV-TW system for a range of mass flow rates of air and water. Incorporating the DC fan and bi-fluid cooling circuits offered favorable features of the system performance while combining the glass cover in front of the PV cell has a conflicting effect. The maximum thermal and electrical efficiencies for average daily evaluation were 79.89% and 10.69% under 300 liters/day for bi-fluid with DC fan glazed and unglazed PV-TW systems respectively. A well matching between theoretical and the experimental results were achieved, where the maximum discrepancy between them was less 4% for the solar cell temperature.

KEYWORDS:

• PV/Trombe wall
• performance
• Bi-fluid
• effect

Nomenclatures

G	=	Solar radiation (W/m2)
E	=	The power output of the PV modules (W)
$T_c$	=	Temperatures of the solar cell (°C)
$T_{f1}$	=	Temperatures of air flow (°C)
$T_a$	=	Ambient temperature (°C)
$T_{f2}$	=	Temperatures of water (°C)
$T_{f2,in}$	=	Temperatures of entering water (°C)
$T_{wall}$	=	The temperature of the outside surface wall (°C)
$T_{out}$	=	Air temperatures of outlet duct (°C)
$T_{in}$	=	Air temperatures of inlet duct (°C)
$T_p$	=	The temperature of plate aluminium (°C)
$m_f$	=	The mass flow rate of air (kg/s)
$c_{pf}$	=	Specific heat of air (J/kg.k)
$h_{c,c-a}$	=	Convection heat transfer coefficient on the outside surface of the solar cell (W/m2.K)
$h_{r,c-a}$	=	radiant heat transfer coefficients on the outside of the solar cell (W/m2.K)
$h_{c,p-f}$	=	Convection heat transfer coefficient from the back surface of the aluminum plate to air flow (W/m2.K)
$h_{r,p-f}$	=	Radiant heat transfer coefficients coefficient from the back surface of aluminum plate to air flow (W/m2.K)
$h_{c,w-f}$	=	Convection heat transfer coefficient from wall to fluid in the duct (W/m2.K)
$V$	=	Ambient wind speed (m/s)
$V_a$	=	The velocity of air flow in the air duct (m/s)
W	=	Width PV-Trombe wall (m)
$X$	=	Height PV-Trombe wall (m)
D	=	The depth of the air duct (m)
Ac	=	Area of PV-Trombe wall (m2)
$A_m$	=	Specific wetted area (m2)
UT	=	Overall heat transfer coefficient between solar cell to ambient (W/m2.K)
Ubottom	=	Heat transfer coefficient from the back surface of the solar cell (W/m2.K)
$I$	=	Electric current (A)
$V_o$	=	The voltage of solar cell (V)

Greek Symbols

${\alpha }_c$	=	absorption factor of the solar cell
${\epsilon }_1$	=	Emissivity factor on the front surface of the PV module
${\epsilon }_2$	=	Emissivity factor on the back surface of the plate aluminum
${\epsilon }_c$	=	Emissivity of the outside of the glass cover
${\epsilon }_a$	=	Emissivity of an ambient environment
${\epsilon }_p$	=	Emissivity of the inside of the plate aluminum
${\eta }_{ele,s}$	=	Electrical efficiency under standard conditions (%)
${\mu }_f$	=	dynamic viscosity of air (Kg/m.s)
${\rho }_f$	=	Density of air (kg/m3)
${\lambda }_f$	=	The thermal conductivity of the fluid (W/m.K)
${\beta }_{pm}$	=	Constant depended on shape porous media
${\eta }_{th}$	=	Thermal efficiency (%)
${\eta }_{ele}$	=	Electrical efficiency (%)
${\beta }_c$	=	Packing factor
${\alpha }_p$	=	Absorptivity of the plate
${\tau }_g$	=	Transmittance factor of the front cover glass of solar cell
${\mathrm{\forall }}_{f2}$	=	A volume of fluid (m3)
${\mathrm{\forall }}_t$	=	Total volume (m3)

Subscripts Abbreviations

C	=	Solar cell
f1	=	Air
f2	=	water
t	=	Tube
c	=	Convective
si	=	Silicon
T	=	Total
p	=	Plate aluminum
r	=	Radiant
G	=	Glass