Evaluation of flux density measurement method for concentrated solar irradiance
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摘要: 为了确定一种新型间接测量太阳能热发电系统聚焦光斑能流密度分布方法的测量误差范围,对其进行了进一步研究。从理论公式出发,分析了该测量方法的误差源;使用球面小定日镜、CCD相机、漫反射板、中性密度滤光片等设备进行了能流密度测量的实验,使用MATLAB软件对实验数据进行处理,得到了漫反射板上聚焦光斑的能流密度分布和总能量;实验时借助全站仪测量并计算了定日镜中心的光线入射角,根据定日镜的面积和反射率、太阳直射辐射值、余弦效率等计算了光斑能量的理论值,并与测量得到的聚焦光斑总能量比较,得出了实验条件下该方法测量光斑总能量以及能流密度的相对误差为3.5%。该测量误差在允许范围内,进一步证实了该能流密度测量方法的正确性和可行性。Abstract: In order to estimate its measurement error range when indirectly measuring the flux distribution on receivers of solar thermal power systems, a new method is studied. The error sources of this method are analyzed based on the theoretical equation. An experiment to measure the flux density distribution of a concentrated beam is implemented with a spherical heliostat, a CCD camera, a diffuse reflector, neutral density filters and other devices. The flux density distribution and total energy of the concentrated solar irradiance on the reflector is calculated with a MATLAB program. The incident angle of rays on the center of the heliostat is measured with a total station. The theoretical value of the beam energy is calculated according to area and reflectivity of the heliostat, the direct normal irradiance and cosine efficiency. By comparing the theoretical value of the beam energy with the measured total energy, the relative error of the total energy and the flux density measured by this method is obtained. The measured relative error is 3.5%.This error is within permission, which further verifies the correctness and feasibility of this new method.
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图 4 OD4滤光片衰减比随波长变化
Figure 4. Attenuation factor of the OD4 filter varies with wavelength changing
表 1 误差源总结
Table 1. Summary of error sources
Error source Relative error/% Pixel value of the CCD camera, PCCD 3.84 Direct normal irradiance, EDNI 0.2 tam2(δsun/2) 3.4 Attenuation factor of the filter, fsun/freceiver 0.5 Reflectance data of the receiver 0.3 
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表 2 实验条件和设备参数
Table 2. Test conditions and device parameters
Date and Time 6/3/2015 9:38 AM(Beijing time) Location Changchun, China Direct normal irradiance/(W·m-2) 870 Reflectivity of the heliostat 0.83 Reflectivity ofthe receiver 0.982 Size of the receiver/m 0.35×0.35 Area of heliostat reflective surface/m 2 0.120 5 Neutral density filter attenuation factor for beam image 1 Neutral density filter attenuation factor for sun image 19 055 Resolution of the CCD camera 1 236×1 628 Pixel size of the CCD/μm 4.40×4.40
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