Optical And Thermal Performance Analysis And Optimization Of Parabolic Trough Solar System

As one kind of sustainable and renewable energy, solar energy plays an important role in issues such as environmental pollution and energy crisis. As a result, solar energy has seen a wide application and a rapid development in recent decades, meanwhile, the input in funds for technology gradually increase. In order to achieve the commercialized and large-scale application, improving the collection efficiency of solar thermal collecting device, lowering the heat loss of the solar system and reducing the cost of construction and operation of thermal power plant and so on becomes a research hotspot.This paper present the refractive surface error transfer process and develop an optical model of solar trough system which considers the refractive surface error. Through comparing the calculation results with the experimental data the optical model is validated. The optimized design parameters are presented based on the maximization of the annual average net heat efficiency. The model is applied to compare the performance of solar parabolic trough system with vacuum tube receiver under two kinds of reflectors, which are glass mirror and film mirror, respectively. Based on the optical model, this paper present a two-dimensional heat transfer model of collector and develop a fast numerical algorithm, the heat transfer model is coupled to the three-dimensional optical model of parabolic trough solar system. In addition, the heat transfer model considers the effect of temperature on thermal properties of material and calculates the radiation heat transfer of two surfaces of collector directly with heat transfer formula, thus boosting the accuracy and reducing the calculation amount. This paper simulates the performance of solar parabolic trough system with two kinds of collectors on and off the irradiation of sun, which are vacuum tube collector and air tube collector, respectively, and compare the simulation results with experimental data and the computed result of other two-dimensional heat transfer model. On the strength of heat transfer model, the effect of external environmental condition, the velocity of heat transfer fluid as well as the optical coefficient of collector on collection efficiency of solar parabolic trough system is also analyzed.The main conclusions of this paper are as follows:(1) There exists about20%relative error of the optical efficiency if the refractive surface error transfer process is ignored. The refractive surface error and the reflective surface error should be considered in predicting the performance of the solar trough system.(2) Both parabolic trough systems with vacuum tube receiver with two kinds of reflectors and north-south axis tracking system are relatively inefficient in winter days, and the net energy output in winter solstice is less than one sixth of the summer.(3) The net heat efficiency of solar trough system with glass mirror is50%less than that of the system with film mirror in the noon of winter solstice and latitude40.(4) The film reflector is more preferable than glass reflector especially in high latitude if they have the same optical property.(5) Under the actual working condition that the operating temperature of parabolic trough solar system is above250℃, the average relative error of collection efficiency calculated by our model is0.91%for vacuum tube collector and0.80%for air tube collector.(6) The effect of the direct normal incidence and the optical coefficient of collector on collection efficiency of solar system is great, in contrast, the effect of the wind speed and the environment temperature as well as the the velocity of heat transfer fluid has less influence on collection efficiency solar system.