A Real-time Solar Dish Monitoring Method Based On Computer Vision

The output of solar thermal power generation is stable and controllable.Under the increasing demand for energy when developing,efficient utilization of solar energy has a tremendous growth potention in the future.Among the four ways of solar thermal power generation,dish Stirling machine has the highest peak photoelectric conversion ratio.And because it can be operated in independent or combined way,which has important applications in various occasions.The solar dish is a point-focusing concentrator with high concentration ratio.This system can produce high temperatures for the following thermoelectric module,so there is little tolerance for poor optical alignment.Improper facet position in solar dish will lead to poor performance and shorten life of device with excessively high flux.Moreover,a variety factors can influence flux density distribution of solar dishes.As the front-end energy part of the dish Stirling machine,the dish concentrating mirror system gathers the parallel incident sunlight into a spot,and get a very high concentration ratio.In practice,the errors of the mirror focusing system will cause the problems of focal spot diffusion,uneven distribution and local hot spots,which directly affects the working temperature and efficiency of the collector,as well as the life of peripheral components.The main factors affecting the performance of the concentrating system are the installation error of the mirror unit,the accuracy of the mirror surface and the interference of external forces on the mirror surface during operation.In order to keep the high efficiency operation of whole system and adjust the system during different circumstance conditions,monitoring the deformation of the facet is necessary.On the one hand,we can infer the distribution of spot energy flow through this system,so as to achieve the function of control and early warning.On the other hand,it can guide the mirror attitude in installation.In the future,each mirror u:nit has its own control unit,and we can use the information from mirror attitude can control them.In this paper,for dish mirror object,various errors affecting performance of dish mirror system are studied.It is found that the errors on mirror surface will only lead to the uniform spread of the spot and the deviation of each mirror unit from the ideal position in the mirror system will lead to unexpect hotspot position.The focal plane is offset by a hot spot or a whole spot in the spot.At the same time,the mathematical analysis and modeling of the mirror element are carried out under the assumption that the facet is a rigid body.And we give the mathematical expression of facet in 3D-space.Based on this,a method based on machine vision is proposed,which can effectively and robustly monitor the mirror pose.At the same time,the data are used to reconstruct the mirror shape,and the Monte Carlo ray tracing model is established to simulate the spot shape near the concentrator.The results show that the simulation results are in good agreement with the experimental one.The average energy flux error between the two methods is about 7%.