Numerical investigation and modelling of controllable parameters on the photovoltaic thermal collector efficiency in semi-humid climatic conditions

ABSTRACT

Hybrid Photovoltaic Thermal (PV/T) systems are energy-generation systems that transform thermal irradiance into both electrical and thermal energy at the same time. Hybrid photovoltaic thermal systems consist of a photovoltaic panel connected to a thermal collector. The main objective of this paper is to find the optimal operating conditions that can be controlled to decrease the photovoltaic panel temperature in order to improve the electrical and thermal performance of PV/T systems. In this work, we proposed the 3D numerical model that is implemented within the COMSOL Multiphysics program to study the PV/T system. The experimental input data being used in this research study reflects a typical Algerian area with semi-humid climate conditions. We study the effect of water velocity, pipe length, diameter, thickness and inlet fluid temperature on the electrical and thermal performance using the design of experiments (DOE) method. Further, the analysis of variance (ANOVA) is used to identify which of these effects impact the most the photovoltaic thermal and electrical efficiencies, the response surface methodology (RSM) is employed to describe how these effects are interacting. Based on ANOVA analysis, the following factors are reported to be important: water velocity, pipe diameter, pipe length and the inlet fluid temperature. Further, there is a significant interactions between water velocity, pipe length and pipe diameter. Among the operating conditions being calculated using the RSM, the optimal one is found when water velocity, pipe length, pipe diameter, pipe thickness and inlet water temperature have the following values, 0.05 m/s, 7.27 m, 0.01 m, 0.0008 m and 10°C, respectively. The corresponding thermal, electrical and overall efficiency were found around 80.73%, 12.87% and 93.60%, respectively. The proposed simulation model provides a reliable framework to study, improve and predict PV/T systems performance whilst ensuring low computational time.

KEYWORDS:

• Photovoltaic thermal system
• 3D numerical model
• finite element method
• response surface methodology
• solar energy

Disclosure statement

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

Nomenclature

Ac	=	PV cell area (m2)
Afc	=	Cross-sectional area of the inlet flow channel (m2)
Cp	=	Specific heat capacity at constant pressure (J kg−1 K−1)
Cpw	=	Specific heat capacity of water (J kg−1 K−1)
Di	=	Inner diameter, m
Ec	=	Total solar energy absorbed into the cell, W
Eel	=	Electrical energy, W
Eth	=	Thermal energy extracted by water, W
hc	=	Convection heat transfer coefficient, W/m2 K
ks	=	Thermal conductivity of the solid, W/m K thermal
kw	=	Thermal conductivity of water, W/m K mass
$\dot{m}$Mass flow rate, kg/s	=
P	=	Pressure, Pa
R	=	Solar irradiance, W/m2
T	=	Variable water temperature, oC
Tamb	=	Ambient temperature, oC
Tc	=	Temperature of PV cell, oC
Tin	=	Water inlet temperature, oC
Tout	=	Water outlet temperature, oC
Tref	=	Reference cell temperature, oC
u, v, w	=	Components of velocity vector, m/s
u	=	Velocity vector field, m/s
U0	=	Inlet water velocity, m/s
ANOVA	=	Analysis of variance
DOE	=	Design of Experiments Method
RSM	=	Response surface methodology
FEM	=	Finite Element Method

Greek symbols

ßref	=	Temperature coefficient at reference cell temperature
ʋ	=	Kinematic viscosity of the water, m2/s
ρ	=	Density of the water, kg/m3
ȠTref	=	PV cell electrical efficiency at reference temperature
Ƞth	=	Thermal efficiency
Ƞel	=	Electrical efficiency
$\overline{{\eta }_{el}}$	=	Average electrical efficiency
ȠTol	=	Total PV/T efficiency
τg	=	Glass Emissivity
αc	=	Absorptivity of PV cell

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/15567036.2022.2125124