Experimental study on the performance of different photovoltaic thermal collectors with nano-technology

ABSTRACT

The process of cooling the photovoltaic cell effectively leads to improving the electrical efficiency of the cell. Herein, the current experimental study employed three different nanofluids (CuO, ZnO, and TiO₂) to cool the PV panel to produce a hybrid collector, also known as a photovoltaic thermal solar collector (PVT). The nanoparticle volume fraction was 0.1, 0.2, and 0.3 vol%. The process of cooling the PV panel was carried out using a copper tube on the back of the PV, which was placed to cover the largest possible area on the back of the PV. Three different flow cross sections – rectangular, square, and circular – were used to compare them. This experimental study was carried out under solar radiation conditions ranging from 450 W/m² to 750 W/m², and the flow rates of the nanofluid were 0.5, 1, 1.5, and 2 L/min. The results show the electrical and thermal efficiency of the PVT system at different conditions. The electrical efficiency increased as a result of adding nanofluid compared to normal water, where the cell with CuO/nanofluids gave the highest value of electrical efficiency at 450 W/m², equaling 11.8%, while it was equal to 11.6%, 11.5%, and 10.8% for ZnO/nanofluids, TiO₂/nanofluids, and water, respectively. An increase in mass flow rate leads to increased thermal, electrical, and combined PVT efficiencies. As well. The high mass flow rate increases the heat transfer coefficients between the tube wall and flowing fluid, which in turn decreases the PV module’s temperature. Finally, the rectangular section and the CuO/nanofluids gave the best value for the electrical power, which reached 83.17 W, and the highest electrical efficiency, which reached 11.5%.

KEYWORDS:

• Electrical efficiency
• nano-technology
• photovoltaic collector
• solar irradiance
• thermal efficiency

Nomenclature

Ac	=	Area of collector (m2)
$C_p$	=	Specific heat capacity of fluid (J/Kg. ℃)
G	=	Solar radiation (W/m2)
Q	=	Heat transfer rate (J/s)
Ta	=	Temperature of standard condition (25°C)
Ti	=	Inlet temperatures of fluid in PVT (℃)
To	=	Outlet temperatures of fluid In PVT (℃)
PVT	=	Photovoltaic thermal
β	=	Temperature coefficient of silicon cell (β = 0.0045°C)
Ø	=	Nanoparticles volume fraction
${\eta }_{PVT}$	=	Efficiency of solar collector
${\mu }_{nf}$	=	Nano fluid viscosity (kg/m. s).
${\mu }_w$	=	Water viscosity (kg/m. s).
${\rho }_f$	=	Density of the base fluid (kg/m3).
${\rho }_{nf}$	=	Density of the Nanofluid (kg/m3).

List of symbols

Ac	=	Function of the collector area (m2)
Cb	=	Conductance of the bond between the fin and tube
Cp	=	Specific heat of the collector cooling medium (J/kg K)
Dh	=	Hydraulic diameter
EAC	=	AC energy output at time t(min), h(hour), d(day), m(month)
EDC,d	=	Daily net DC energy output (kWh/d)
F	=	Fin efficiency factor
${\mathrm{F}}^{-}$	=	Corrected fin efficiency
FR	=	Heat removal efficiency factor
I(t)	=	Solar irradiance (w/m2)
hfi	=	Heat transfer coefficient of fluid (W/m2 K)
Ht	=	Plane-of-Array (POA), solar irradiation (kwh/m2)
Kabs	=	Absorber thermal conductivity
Kpv	=	Photovoltaic module conductivity
Labc	=	Absorber thickness
LPV	=	Photovoltaic module thickness
m•	=	Mass flow rate (kg/s)
PPV,rated	=	PV array rated power (kw)
Qu	=	Actual useful heat gain (W)
S	=	Absorbed solar energy (W)
Tp	=	Photovoltaic collector temperature (C o)
Ta	=	Ambient temperature (C o)

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Notes on contributors

Ebrahim Hajidavalloo

Ebrahim Hajidavalloo is Professor of Mechanical Engineering, Department of Engineering, Shahid Chamran University. Dr. Hajidavaloo's research covers a wide range of topics in heat transfer thermodynamics, multiphase flow, advanced numerical methods, thermal power plants, refrigeration, fluid mechanics, and convection.