Experimental study of a novel photovoltaic-thermal-thermoelectric generator-based solar dryer for grapes drying

ABSTRACT

 In the present work, a novel photovoltaic-thermal-thermoelectric generator (PVT-TEG) based solar dryer has been developed, and its drying performance is experimentally investigated and compared with open sun drying (OSD). The reason for incorporating the PVT-TEG system in the solar dryer is to improve the system’s utility in practical drying applications by augmenting electrical power generation with the combination of PV and TEG along with extracting thermal energy for drying, thereby improving the overall system efficiency. Grapes drying has been performed to analyze the drying process and thermal and electrical performance of the system. The moisture content level after the experiment is evaluated as 1.71 (d.b.) from an initial value of 4.00 (d.b.) in PVT-TEG solar drying compared with 2.51 (d.b.) in OSD. The findings of the drying performance are determined as 17.81% for drying efficiency, 1.10 kWh/kg for specific energy consumption, and 0.68 kg/kWh for specific moisture extraction rate. The energy efficiencies obtained for the experiment are PV panel efficiency of 14.07%, TEG efficiency of 11.64%, PVT efficiency of 72.36%, and thermal efficiency of 48.50%. When compared to the open literature, the utility of the present novel dryer is found in terms of its enhanced drying and energy performances.

KEYWORDS:

• Photovoltaic thermal
• Thermoelectric generator
• Energy and mass balance
• Hybrid solar dryer
• Grapes drying

Nomenclature

$T_c$	=	Cell temperature (℃)
$T_o$	=	Standard test temperature (℃)
${\beta }_o$	=	Standard efficiency factor (-)
${\eta }_o$	=	Standard efficiency (%)
${\alpha }_c$	=	Absorptivity of cell (-)
$T_{\mathit{amb}}$	=	Ambient temperature (℃)
$I_t$	=	Solar radiation (W/$m^2$)
$A_m$	=	Area of module ($m^2$)
${\tau }_g$	=	Transmissivity of glass material (-)
${\beta }_c$	=	Packing factor of photovoltaic panel (-)
$\mathit{G}$	=	Solar irradiance (W/$m^2$)
$K_{\mathit{TEG}}$	=	Thermal conductance (W/m K)
$S_{\mathit{TEG}}$	=	Seebeck coefficient (V/K)
$R_{\mathit{TEG}}$	=	Electrical resistance (Ω)
$I_{\mathit{TEG}}$	=	Operating current of TEG (A)
$T_{\mathit{h},\mathit{TEG}}$	=	Hot side temperature of TEG (℃)
$T_{\mathit{c},\mathit{TEG}}$	=	Cold side temperature of TEG (℃)
$m_f$	=	Air mass flow rate (kg/s)
$C_f$	=	Specific heat of air (J/kg K)
$h_{\mathit{c},\mathit{TEG}}$	=	Convective heat transfer coefficient of TEG (W/$m^2\mathit{K})$
$T_f$	=	Working fluid temperature (℃)
$T_{\mathit{fi}}$	=	Inlet fluid temperature (℃)
$T_{\mathit{fo}}$	=	Outlet fluid temperature (℃)
$A_c$	=	Area of collector ($m^2$)
$A_{\mathit{TEG}}$	=	Area of TEG ($m^2$)
${\phi }_1$	=	Relative humidity at inlet (%)
${\phi }_2$	=	Relative humidity at outlet (%)
$m_C$	=	Mass flow rate of crop (kg/s)
$q_1$	=	Heat of the product at inlet of dryer (J/kg)
$q_2$	=	Heat of the product at outlet of dryer (J/kg)
$h_{\mathit{f}1}$	=	Enthalpy of fluid at inlet of dryer (J/kg)
$h_{\mathit{f}2}$	=	Enthalpy of fluid at outlet of dryer (J/kg)
$h_f$	=	Latent heat of vaporization (J/kg)
$A_d$	=	Area of dryer cabin ($m^2$)
$T_{\mathit{cp}}$	=	Crop temperature (℃)
$T_{\mathit{dc}}$	=	Dryer cabin temperature (℃)
$h_{\mathit{cpc}}$	=	heat transfer coefficient of crop to the dryer cabin (W/$m^2\mathit{K})$
${\eta }_{\mathit{PVT}}$	=	Photovoltaic thermal efficiency (%)
${\eta }_{\mathit{TEG}}$	=	Thermoelectric generator efficiency (%)
${\eta }_O$	=	Overall efficiency (%)
$Q_{\mathit{h},\mathit{TEG}}$	=	Absorbed energy flow in TEG (W)
$Q_{\mathit{c},\mathit{TEG}}$	=	Dissipated energy flow in TEG (W)
$P_{\mathit{TEG}}$	=	Power output of TEG (W)

Disclosure statement

No potential conflict of interest was reported by the author(s).