Study On The Characteristics And Structure Optimization Of Two - Stage System Of Solar Energy Focused Electric Heating

The proposed trough concentrating solar thermal power two-stage system based on the trough concentrating PV/T system, increased in the metal cavity heating stage. It is used to heat the cooling working medium which recovered thermal energy of solar cells, in order to maintain output solar cell efficiency and output high quality thermal energy to meet the using heat of production and living. Using the methods combined theoretical and experimental, the transducer characteristics and system architecture optimization of the trough concentrating solar thermal power two-stage system have a comprehensive study. In this paper, the following conclusions:(1) Under the conditions of the different concentrating light intensity and the different concentration ratio, the solar cell working temperature and light intensity on the PV/T cavity affect the characteristics of electrical energy output have been studied. The coupling correlation data between the space solar cell output characteristic: open circuit voltage, short circuit current, fill factor, the maximum output power, solar cell efficiency and battery temperature, light intensity is establishing. In the results, PV/T cavity away from the focal plane in a certain position, the mirror opening width of PV/T from 57 cm to 157 cm, the short-circuit current, relative maximum power is respectively decreased 27.16%, 27.01%; the open circuit voltage, solar cell efficiency is respectively increased by 2.19%, 83.45%. This shows, within a certain range, with the opening width of the trough concentrating mirror reduced, the geometric concentration ratio is lowered; the space solar cells efficiency will increase. With the increase in the opening width of the trough concentrating mirror, the other output parameters of space solar cells will increase.(2) The photo-carrier generation, recombination and transport large differences at different positions of the solar cell caused by the uneven radiation energy flux of the solar cell surface, resulting in the solar cell performance and life expectancy declined. The output characteristics of a solar cell array at different positions of PV / T cavity away from the focal plane and different opening width of PV/T stage mirror have tested using experimental method, It can reveal the uneven energy flux impact on the photoelectric conversion overall performance of the solar cell chip, and determine the placement position of a certain size space solar or PV/T cavity and the optimal opening width of the mirror. In the results, when PV/T cavity 5cm away from the focal plane and the mirror opening width of 157 cm, the maximum output power get its maximum value of 22.3678 W, the solar cell efficiency was 2.74% at this time. When PV/T cavity 3cm away from the focal plane and the mirror opening width of 57 cm, the solar cell efficiency achieved maximum value of 5.71%, the maximum output power was 17.916 W at this time. When PV/T cavity 1cm away from the focal plane and the mirror opening width of 157 cm, the thermal efficiency obtained maximum value of 58.9%, and the cooling working fluid temperature was 0.68 ℃, the solar cell efficiency was 2.2% at the same time.(3) Solar radiation energy in PV/T stage and the metal cavity heating stage in two-stage system have been realization photovoltaic and photothermal conversion. The energy flux distribution between the metal cavity heating stage and PV/T stage is a key factor influence on the thermal, photovoltaic conversion efficiency of the system. On the premise of ensuring the solar cell efficiency, in order to improve the thermal quality of the system, this paper achieve the output performance of the system on the increasing concentrating area of the heating stage by increasing the heating stage metal cavity lengths of the of different by experiment. The results shown that in 1.8m2 mirror PV/T stage and 30m2 mirror heating stage system, when the solar cell temperature is 73 ℃, the output working fluid temperature of the metal cavity heating stage is 62.38 ℃, increased by 12.06 ℃, the transient thermal efficiency is 47.26% at the same time. In direct radiation of 992 w·m-2, 1000 w·m-2, the temperature rise of the metal cavity heating stage was respectively 12.87 ℃, 13.32 ℃, compared with the direct radiation 896 w·m-2 of 1.8m2 mirror PV/T stage and 15 m2 mirror heating stage system, respectively increased by 74.86%, 80.98%.(4) The number of the cooling working fluid cycles in the system directly determines the output heat of the system. In order to optimize the system structure, the output thermal properties of a trough concentrating thermal power two-stage system in a single-cycle and a closed cycle was tested using experimental method. The results showed that when the direct radiation of 978 W·m-2 in a closed cycle, the thermal efficiency of the PV/T stage, the thermal efficiency of the heating stage, the solar cell efficiency of the system respectively 44.93%, 47.26%, 2.06%. Compared with the direct radiation of 992 W·m-2 in single cycle, relatively reduced by 21.48%, 4.97%, 20.77%. Experiments run 10 minutes later, the temperature of the working fluid in the tank is 46.7 ℃, increased of 10.85 ℃, the thermal efficiency of the 1.8m2 mirror PV/T stage and 30 m2 mirror heating stage system is 22.38%. The experimental run 20 minutes later, the temperature of the working fluid in the tank is 54.45 ℃, increased of 18.6 ℃. The experimental run 30 minutes later, the temperature of the working fluid in the tank 62.8 ℃, increased of 28.7 ℃.(5) The PV/T stage, the metal cavity heating stage were respectively optimization the position of PV/T cavity, mirror opening width of the PV/T stage, thermal heating methods and metal cavity structural of thermal main output unit of the metal cavity heating stage, and then obtain the matching and operating parameters of system between the PV/T stage and the metal cavity heating stage.This paper proposes a trough concentrating thermal power two-stage system, to ensure output the solar cell efficiency and output required quality thermal energy at the same time. The conclusions propose the support for further development, application of basic theory and preliminary experimental.