| The development of a price-competitive concentrating collector is the key to its application for the medium-temperature solar thermal utilization system.The optical efficiency of dish concentrating mirror field is excellent with high cosine efficiency,and there is no block loss.However,there are certain shortcomings in the processing,installation and commissioning,or the uniformity of energy distribution in traditional parabolic dish concentrators,which makes the cost of dish system remain high.In this paper,a quickly adjusted model and algorithm for Fresnel dish concentrator are proposed,which can not only significantly simplify the alignment process in the installation of concentrators,but also reduce the cost.It is very suitable for the use of fragmented idle space to build distributed renewable energy system.Theoretical analysis and exploration are from the following aspects:(1)A specular model of the Fresnel dish concentrator is proposed.The plane facets are configured in a multi-circle circular array instead of curved mirrors,which solves the high cost of the special manufacturing requirements of the mirrors.For Fresnel dish concentrators,the effect of size,circles and numbers of facets on concentrator performance are analyzed.The results show that the geometric concentration ratio increases with the decrease of facet size and the increase of circles,when the concentrator radius is certain.The increase of concentration ratio is faster with the increase of facet circles,but the cost increases accordingly.(2)The algorithm for determining inclination of facets rapidly is proposed.The optimum inclination angles of each circle-facets are calculated,and the focal spot radius of the circle mirror on the focal plane is minimum.It is considered that spot radius of the circle-facets on focal plane is the minimum value,when the spot sizes reflected by the center point of one mirror attains a minimum.That is,the posture of facets can be determined by the reflected spot sizes.(3)The energy flux distribution of Fresnel dish concentrator on focal plane is analyzed.TracePro optical software is used to simulate the change of focal spot of each circle-facets under different inclination angles and heights of heat absorber.The results of focal spot simulation analysis verify the correctness of the algorithm.Combining the calculation formulas of heat collecting efficiency ?c and energy flux distribution uniformity ?f,the performance of the energy density of the focal plane that has been obtained is analyzed.When heat absorber height is 1349 mm,98.7% of the energy on focal plane is distributed within a radius of 112 mm.And the energy distribution on absorbing surface is more uniform.(4)The supporting structure of Fresnel dish concentrator and the focusing system of facets are designed.All the facets are adjusted in same plane at the initial state,the concentrator can simultaneously set the inclination angle of all the facets instead of each facet.The rapid and accurate attitude adjustment of the concentrator is realized.The adjusting bars are removed once the adjustment is completed.The same set of focusing mechanisms can be reused multiple times,thus the cost is reduced. |
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