Effect of non-uniform illumination on performance of solar thermoelectric generators

doi:10.1007/s11708-018-0533-7

Front. Energy

2018, Vol. 12

Issue (2) : 239-248 https://doi.org/10.1007/s11708-018-0533-7

RESEARCH ARTICLE

Effect of non-uniform illumination on performance of solar thermoelectric generators

Ershuai YIN¹, Qiang LI¹(

), Yimin XUAN²

¹. MIIT Key Laboratory of Thermal Control of Electronic Equipment, School of Energy and Power Engineering, Nanjing University of Science and Technology, Nanjing 210094, China
². IMIIT Key Laboratory of Thermal Control of Electronic Equipment, School of Energy and Power Engineering, Nanjing University of Science and Technology, Nanjing 210094, China; School of Energy and Power, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

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Abstract

Solar thermoelectric generators (STEGs) are heat engines which can generate electricity from concentrated sunlight. The non-uniform illumination caused by the optical concentrator may affect the performance of solar thermoelectric generators. In this paper, a three-dimensional finite element model of solar thermoelectric generators is established. The two-dimensional Gaussian distribution is employed to modify the illumination profiles incident on the thermoelectric generator. Six non-uniformities of solar illumination are investigated while keeping the total energy constant. The influences of non-uniform illumination on the temperature distribution, the voltage distribution, and the maximum output power are respectively discussed. Three thermoelectric generators with 32, 18 and 8 pairs of thermocouples are compared to investigate their capability under non-uniform solar radiation. The result shows that the non-uniformity of the solar illumination has a great effect on the temperature distribution and the voltage distribution. Central thermoelectric legs can achieve a larger temperature difference and generate a larger voltage than peripheral ones. The non-uniform solar illumination will weaken the capability of the TE generator, and the maximum output power decrease by 1.4% among the range of non-uniformity studied in this paper. Reducing the number of the thermoelectric legs for non-uniform solar illumination can greatly increase the performance of the thermoelectric generator.

Keywords solar thermoelectric generators non-uniform solar illumination performance evaluation solar energy

Corresponding Author(s): Qiang LI

Issue Date: 04 June 2018

Cite this article:

Ershuai YIN,Qiang LI,Yimin XUAN. Effect of non-uniform illumination on performance of solar thermoelectric generators[J]. Front. Energy, 2018, 12(2): 239-248.

URL:

https://academic.hep.com.cn/fie/EN/10.1007/s11708-018-0533-7
https://academic.hep.com.cn/fie/EN/Y2018/V12/I2/239

Fig.1 Schematic diagram of STEGs

Fig.2 Structure diagram of the TE generator with 32 pairs of thermocouples

Fig.3 Properties of Bi₂Te₃ semiconductor materials

Fig.4 Heat fluxes of six uniformities at a solar radiation density of 10000 W/m²

Tab.1 Parameters for the simulation

Fig.5 Temperature distribution of TE generator under six non-uniform solar illuminations at G₀ = 50 kW/m², r_e = 1.84 W, and h = 10000 W/(m²?K)

Fig.6 Influence of solar illumination non-uniformity on temperature of thermoelectric legs at G₀ = 50 kW/m², r_e = 1.84 W, and h = 10000 W/(m²?K)

Fig.7 Voltage distribution of TE generator at a uniform radiation of G₀ = 50 kW/m², r_e = 1.84 W, and h = 10000 W/(m²?K)

Fig.8 Generated voltage of each thermoelectric semiconductor leg at r_e = 1.84 W and h = 10000 W/(m²?K)

Fig.9 Influence of solar illumination non-uniformity at G₀ = 50 kW/m² and h = 10000 W/(m²?K)

Fig.10 Influence of number of thermoelectric legs on total performance of STEG

C_P	Specific heat capacity/(J?(kg?K)^-¹)
T	Temperature/K
t	Time/s
$q →$	Heat flux vector/(W?m^-²)
$q ˙$	Heat generation rate/(W?m^-³)
$∇$	Hamiltonian
s	Seebeck coefficient/(V?K)
k	Thermal conductivity/(W?(m?K)^-¹)
$J →$	Electric current density vector/(A?m^-²)
$E →$	Electric field intensity vector/(V?m^-¹)
$D →$	Electric fluxdensity vector/(A?m^-²)
Z	Figure of merit of TE generator
G	Solar radiation density/(W?m^-²)
D²	Variance of Gaussian distribution
G₀	Density of uniform radiation/(W?m^-²)
A_s	Area of selective absorber/m²
Q	Heat flux density/(W?m^-²)
P	Output power of TE generator/W
V	Voltage/V
r	Resistance/W
r	Density/(kg?m^-³)
s	Electrical conductivity/(S?m^-¹)
j	Electric scalar potential/V
p	Eircumference ratio
w	Normalization factor
t	Transmittance of the glass
a	Absorptance of the solar selective absorber
e	Emissivity of selective absorber
e	External resistance
oc	Open circuit voltage
max	Maximum output power of TE generator
TE	Thermoelectric generator

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