Enhancement of a photovoltaic cell performance by a coupled cooled nanocomposite thermoelectric hybrid system, using extended thermodynamics

Abstract

A new analytical mathematical model is developed, describing a cooled photovoltaicthermoelectric hybrid system. The thermoelectric material is a nanocomposite where the model takes into account size-dependent non-local thermoelectric properties from an extended thermodynamic point of view. The photovoltaic device powers also the cooling system. The model determines first the optimum thickness of the photovoltaic device, then studies the influence of several size-related parameters on the thermoelectric efficiency (also related to the figure of merit) and finally, coupled to a cooling device, the overall efficiency. For the photovoltaic part, the model is applied to two materials, mono-crystalline and poly-crystalline silicon. The thermoelectric part of the model is applied to an n-leg nanocomposite made out of Sb2Te3 nanoparticles in a Bi2Te3 matrix and of a p-leg nanocomposite made out of Bi2Se3 nanoparticles in a Bi2Te3 matrix. An optimal total photovoltaic device size has been found to be around 127 µm and 1.25 µm for the mono-and poly-crystalline silicon, respectively, leading to efficiencies up to 20 %, depending on photovoltaic recombination characteristics. With the cooling device, the overall efficiency was increased by up to an additional 10 % (an increase of almost 50 %), leading to overall efficiencies around 25 %. IntroductionDevelopments in renewable energy seek to alleviate the global energy crisis and reduce its impact on the environment. One way is to use solar energy. By means of photovoltaic (PV) solar cells, photonic energy is mainly converted into electricity and waste heat. PV cells have relatively low conversion efficiency, because they can only utilize part of the incident solar energy due to its given bandgap, and require often hybrid configurations [1]. One way to increase the efficiency of PV cells is using thermal management by means of heat sinks [2]. Otherwise, the waste heat can be used in order to be converted to more electricity via thermoelectric devices (TE) [3][4][5][6]. As a common PV cell converts a large amount of solar irradiant energy into heat, a hybrid PV cell and TE device (PVTE) may be a prospective way to improve the overall efficiency of solar energy [7]. One form of PVTE systems uses the socalled spectrum splitting concentrating system, where the photons with an energy out of the PV working waveband are incident to the TE devices, generating thereby electricity via the thermoelectric effect [8][9][10]. This system is complex and the heat produced from the PV is still not used. Connecting the TE device directly at the dark side of the PV cell is simpler and theoretically all thermal energy can be used by the TE device [11], of which the efficiency can be even increased by cooling the TE device [7,12]. It is the latter hybrid system that we consider in this work. As the efficiency in TE devices are proportional (though not necessarily linearly) on mainly the temperature difference across the device and the figure of merit, both are to be increased. The temper...

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