Experimental analysis of photovoltaic-thermal collectors with closely spaced tubes

ABSTRACT

Solar Photovoltaic (PV) systems have become increasingly popular in the last decade due to continuous increase in conversion efficiency and significant reduction in per unit generation cost. Photovoltaic-thermal (PV/T) collectors have been gaining popularity to utilize Sun’s spectrum effectively for production of electricity and utilization of waste heat. In the present study, two independent serpentine PV/T collectors having small gap between tube columns are designed to obtain desired temperature for domestic use with limited collector area and to achieve better cooling uniformity. PV/T-I has a copper absorber plate attached to the rear surface of the PV module and tubes are brazed to the plate, while PV/T-II has only tube for fluid flow which is glued to the PV back. Both the PV/T’s have a back cover to protect the tubing from moisture and dust. PV/T’s are tested under outdoor conditions during September–December, 2018. The developed PV/T’s are analyzed using the energetic and exergetic method. The average energy and exergy efficiency for PV/T-I is found to be 62.28 ± 5.53% and 12.27 ± 5.58%, whereas for PV/T-II average energy and exergy efficiency found to be 51.13 ± 5.53% and 13.4 ± 5.58%, respectively.

KEYWORDS:

• PV/T solar collector
• serpentine collector
• absorber plate
• thermal efficiency
• exergy efficiency
• heating rate
• hot spot investigation

NOMENCLATURE

$A_C$	=	collector area, $m^2$
$c_p$	=	specific heat at constant pressure, $\mathrm{J}/\mathrm{k}\mathrm{g}\mathrm{K}$
$\dot{E}{x}_{el}$	=	electrical exergy input, $W$
$\dot{E}{x}_{in}$	=	exergy input, $W$
$\dot{E}{x}_{out}$	=	exergy output, $W$
$\dot{E}{x}_{th}$	=	thermal exergy input, $W$
$G$	=	solar radiation, $\mathrm{W}/{\mathrm{m}}^2$
$I_m$	=	current at maximum power point, $A$
${\dot{m}}_{\hspace{0.17em}}$	=	mass flow rate of fluid, $kg/s$
$T_a$	=	ambient air temperature, $\mathrm{K}$
$T_{fi}$	=	fluid inlet temperature, $\mathrm{K}$
$T_{fo}$	=	fluid outlet temperature, $\mathrm{K}$
$T_p$	=	PV surface temperature, $\mathrm{K}$
$T_{sun}$	=	temperature of the sun, $\mathrm{K}$
$V_m$	=	voltage at maximum power point, $V$
v	=	wind speed, $m/s$
Greek symbols	=
${\eta }_{el}$	=	electrical efficiency of PV/T, %
${\eta }_{en}$	=	overall energy efficiency of a PV/T, solar collector, %
${\eta }_{ex}$	=	exergy efficiency of PV/T, %
${\eta }_{th}$	=	thermal efficiency of PV/T, %

Additional information

Notes on contributors

Dudul Das

Mr. Dudul Das is a Research Scholar in the Centre for Energy at Indian Institute of Technology Guwahati, India. His current research includes solar PV/T collector design and performance investigation.

Pankaj Kalita

Dr. Pankaj Kalita is an Assistant Professor in the Centre for Energy at Indian Institute of Technology Guwahati, India.  His current research includes solar energy conversion, thermochemical and biochemical conversion, fluidized bed technologies, energy management, energy storage (Li-ion and thermal energy), and integration of renewable energy for remote electrification.