Performance analysis and test on concentration solar thermoelectric generation device

Abstract: Due to environmental and energy security concerns, many researches are being conducted in harvesting the energy of the sun. Thermoelectric is one material which generates a voltage in the presence of a temperature gradient. When these materials are sandwiched between a solar absorber and a heat sink to establish a temperature difference and generate power, they are called solar thermoelectric generators (STEGs), converting solar power to electric power. In this paper, we conducted performance analysis and testing of a concentration solar thermoelectric generation device based on thermoelectric generator (TEG). The device included an electrical generating unit with 10 serially connected thermoelectric modules using a traditional semiconductor material, Bi2Te3. The semiconductor was illuminated by concentrated solar radiation on hot side and cooled by running water through flat heat pipe on the cold side with the condensation of the heat pipe in water tank and the evaporation of the heat pipe connected with the cold side of TEG. A sun-tracking parabolic trough concentrators was used to concentrate solar radiation. Its orientation towards the sun was achieved with a stepper motor. In order to express the performance of concentration solar thermoelectric power generation system accurately, a comprehensive energy transfer model was established, the simulation results showed that when the ambient temperature were constants, the increases of solar irradiance making the solar-thermal conversion efficiency dropped from 58.86% to 54.94%, but thermoelectric conversion efficiency was enhanced from 1.17% to 6.15%. Under the influence of processing technology and materials, even if the same type of thermoelectric modules under the same temperature difference, open circuit voltage and internal resistance were different. When in series with 10 modules, the temperature at the hot side of thermoelectric modules were different spatially due to uniformed heat flow. fl At the same time, due to effect of peltier the temperature of the modules changed along with the different of output power, these factors would lead to different output characteristic of each thermoelectric module. When multiple modules were in series together, it can't make each module working at maximum power output state, resulting in the overall electric energy production reduced. In this research, we used centralized-distributed-hybrid MPPT (Maximum Power Point Tracking) control scheme to overcome the maximum power points mismatching among different thermoelectric generator modules and maximized the energy efficiency of the device. The results of tests showed that the output power of TEG with MPPT was achieved fast, accurately and steadily, and in 30 minutes working time the average power added 3.2 W. In addition, we determined the influence of water flow quantity and optimal load for the performance. The results showed that when flow quantity was less than 8 L/min, temperature of heat pipe condensation and TEG cold side were drop rapidly. But when the flow quantity was greater than 8 L/min, the temperature change was flat out. Output power was rising along with the increase of temperature difference. The maximum power was 30.2 W. The optimal match load was near resistance when temperature difference was low. The optimal load increases gradually along with the increase of temperature difference. The optimal load resistance was 38 Ω with temperature difference of 150 K. Whole day tests for the device have done during the 08:00-16:00 on June 16, 2015, from which the output power smoothly changing and it was between 22.8-30.1 W. With eight-hour test, the average power was 27.8 W, and the electric quantity was 222.4 W?h. The thermoelectric conversion efficiency was up to 5.4% and the maximum efficiency of the device was 4.1%. These test results were consistent with theoretical model analysis. The concentration solar thermoelectric generation device is solid-state device, it has no moving parts, which increases reliability and reduces maintenance. It has many applications such as rural electrification in developing countries and power supply for remote sensors.