线性菲涅尔一次镜场光学效率分析

Optical efficiency analysis of primary linear Fresnel reflectors in CSP

对线性菲涅尔太阳能集热一次镜场的光学效率进行了数值计算。用最大采光半角θ、反射镜列数n和镜场填充率μ来描述镜场,计算一次镜场光学效率随光线入射角γ的变化趋势。该算法的计算结果与Trace Pro及Sol Trace的计算结果一致。分析表明：线性菲涅尔一次镜场的光学效率受相邻反射镜列间的遮挡和阴影影响,加大光线入射角,镜场效率明显下降;在无阴影和无遮挡的情况下,随着入射角γ的增加,与光线垂直入射相比,镜场效率按cosγ/2倍率下降。通过计算得到光线垂直入射时,镜场不发生遮挡的临界镜场填充率及其对应的光学效率。研究结果显示：减小最大采光半角能显著增加镜场光学效率;当最大采光半角为45~60°、在正午前后6~8 h,不发生阴影和遮挡的临界镜场填充率一般低于75%;与抛物线槽式聚光器相比,设计良好的线性菲涅尔一次镜场反射镜的阴影和遮挡,使正午前后6~8 h的平均光学效率下降5.0%~8.3%。

Numerical algorithm has been developed to calculate the optical efficiency of the primary LFR system. The half maximum light receiving angle θ,mirror rows n and filling factor μ are used to describe the primary LFR system. The optical efficiency is calculated as the incident angle changes,by algorithm proved by comparison with Trace Pro and Sol Trace simulations. It is found from the analysis that the LFR system optical efficiency is influenced by blocking and shadowing between adjacent mirror rows,causing reduction as the incident angle increases. If there is no blocking and shadowing,the efficiency is cosγ/2 times the perpendicular incidence efficiency. Critical mirror filling factor,if reached blocking and shadowing will happen,is given for perpendicular incidence from the calculation,together with the corresponding efficiency. The optical efficiency of the LFR system can be improved remarkably by reducing the half maximum light receiving angle. The critical mirror filling factor,for the LFR system with the half maximum light receiving angle between 45 ° and 60 °,during the 6 ~8 hours around noon, should be smaller than 75%. Compared with PTC technology,the shadowing and blocking effects caused a reduction of 5.0%~8.3% in optical efficiency during the 6~8hours around noon for an optically optimized LFR.