Optimal design method for concentrating photovoltaic-thermoelectric hybrid system

Utilizing the dissipated thermal energy by photovoltaic cells working as the heat source of thermoelectric module to generate extra electricity is an optional way to further improve the photoelectric conversion efficiency of concentrating photovoltaic system. However, there exists a confrontation between the efficiency temperature characteristics of the photovoltaic cell and the thermoelectric module. The photovoltaic efficiency decreases with the rise of its temperature while the thermoelectric efficiency increases with its temperature difference augmenting, which makes the design of the concentrating photovoltaic-thermoelectric hybrid system crucial. In this paper, the selection principle of the coupling devices and a novel optimal design method for the concentrating photovoltaic-thermoelectric coupling system are proposed. The minimum figure of merit of the thermoelectric generator that enables the efficiency of the concentrating photovoltaic-thermoelectric hybrid system to be larger than that of the concentrating photovoltaic system is calculated and regarded as the reference of evaluating the feasibility and selecting the coupling devices. For the optimal designs, the temperature distribution where the concentrating photovoltaic-thermoelectric hybrid system has the highest electric efficiency is firstly calculated. Then, the optimum thermal resistance of the thermoelectric generator, which keeps the photovoltaic-thermoelectric hybrid system operating at the optimal temperature distribution, is calculated. Once the thermoelectric thermal resistance is obtained, the optimal structure of the thermoelectric generator can be determined. The effects of reference efficiency, the efficiency temperature coefficient of the photovoltaic cell, the figure of merit of the thermoelectric module and the convective heat transfer coefficient of the cooling system on optimal designs of the concentrating photovoltaic-thermoelectric hybrid system are also discussed.