Performance Analysis And Optimization Of Trough Compound Parabolic Concentrating Energy Supply Device

In order to improve the energy supply capacity of the compound parabolic concentrator(CPC)in cold regions during winter,and create conditions for the energy supply device to be driven independently by solar energy.The energy supply device can realize the re-reception and photoelectric conversion of the incident radiation that is not converted by photothermal conversion by adding a photovoltaic module with a mirror on it’s backside at the aperture of the traditional CPC.Then the heat generated in this process can melt the frost on the surface of the glass cover plate.In this paper,the influence mechanism of different incident angles,air flow rates,receiver shapes and other working conditions on the photothermal and photoelectric conversion performance of the energy supply device and the defrosting characteristics of the winter glass cover is explored by theoretical calculation,simulation and experimental test.It provides theoretical basis and experimental data for the practical application of the energy supply device.Firstly,the size and position of the photovoltaic module are calculated by optical simulation software,and the variation of the light loss rate of the energy supply device and the same specification CPC is compared and analyzed.The results show that in the radial incident angle range of 0 °≤α≤24 °,the light escaping rate of the energy supply device is 12.0 %,which is 15.5 % lower than that of the same specification CPC.The energy supply device with ’*’ shaped receiver had less escaped light,and the light escaping rate is26.0 %,which is 1.3 % lower than that of ’+’ shaped receiver.Based on the theory of heat transfer,the heat transfer model of air medium in the energy supply device is established,and the heat transfer characteristics of air medium in the ideal state are simulated and calculated.The results show that the outlet temperature of single-layer glass tube with ’*’shaped receiver is 43.4 °C,which is 8.2 °C higher than that of single-layer glass tube with’+’ shaped receiver.Based on the research of simulating calculation,a performance testing system of trough compound parabolic concentrating energy supply device is built.Under actual weather conditions,the solar energy conversion performance and winter defrosting characteristics of the energy supply device and the same specification CPC were compared and tested.The results show that when the midday solar irradiance is 706.0 W,the ambient temperature is 16.1 °C,and the air velocity is 4.6 m/s,the photothermal conversion efficiency of the energy supply device is the highest at 75.7 %.The daily heat collection of the energy supply device with the ’*’ shaped receiver is 9.6 MJ,which is about 31.7 %higher than that of the energy supply device with the ’+’ shaped receiver.Under the same working conditions,the daily heat collection of the energy supply device is 11.7 MJ,the total conversion efficiency is about 75.1 %,and the output power of the photovoltaic module is 190.0 W,which is higher than that of the same specification CPC.In cloudy weather,the cumulative heat collection and total conversion efficiency of the energy supply device are higher than that of the CPC of the same specification,which are 5.0 MJ and 66.3 %,respectively.The energy supply device can output an additional power of 178.1 W.During the winter operation,the energy supply device can use the heat energy generated in the photoelectric conversion process of oblique incident solar radiation to melt the frost on the surface of the glass cover,shorting the defrosting time of the energy supply device,reducing the heat loss of defrosting,and extending the daily heat collection and energy supply time.The defrosting time and the temperature of the glass cover are used as the characterization parameters of the defrosting characteristics of the energy supply device,and the defrosting characteristics of the energy supply device and the same specification CPC are compared and tested in winter.The results show that under the same operating conditions,the temperature of the frosting layer on the surface of the glass cover of the energy supply device is 9.3 °C higher than that of the same specification CPC glass cover plate at the same time,and the defrosting time is shortened by 42 min.The defrosting speed of the energy supply device is 27.2 °C/h,which is 27.1 % faster than that of the same specification CPC.