【作者】 张谦；

【导师】 胡芃； 程晓舫；

【作者基本信息】 中国科学技术大学 ， 工程热物理， 2013， 博士

【摘要】 目前,人类赖以生存发展的化石能源面临着严重的需要解决的问题：首先是全球已探明的化石能源储存量有限,不可再生能源很快将会消耗殆尽；其次,化石能源的消耗带来了严重的环境问题,如温室效应、大气污染等。因此,开发和利用可再生能源十分必要和紧迫。太阳能作为一种取之不尽、用之不竭的清洁可再生能源,近年来受到了越来越多的重视。但太阳能辐射能流密度较低,制约了其应用。开发具有实用价值的低成本、高效率、高稳定性的太阳能聚光器,是提高太阳能辐射能流密度最有效的途径,能够进一步促进太阳能的广泛应用。而传统聚光器,如槽式、碟式和塔式太阳能聚光器,在加工、安装维护,或聚光能流密度均匀性等方面均存在一定的缺点。因此,本文在传统聚光器的基础上,提出了一种新型线性菲涅耳反射太阳能聚光器，一种分频聚光光伏光热综合利用系统,以及一种分段槽式太阳能聚光系统,并依托国家重点基础研究发展计划(973)计划(NO：2010CB227305),中科院太阳能行动计划(No.CX2090130012),开展了相关理论和实验研究。首先,提出了新型线性菲涅耳玻璃镜面反射聚光器的结构设计原理。该系统主要包括三个部分,反射玻璃镜面、平板框架以及聚光接收体。条形玻璃镜面的宽度和倾斜角度随自身所处位置、聚光接受体形状尺寸和安放角度以及是否考虑太阳入射光立体角影响等因素确定,并给出了无量纲理论公式。数值分析表明系统理论聚光比、面积利用率主要与聚光接收体的安装高度和镶嵌玻璃镜面的平板框架尺寸有关；聚光接收器为平板型时,其安装角度对理论聚光比和面积利用率的影响不大；为圆柱体时,理论聚光比与反射镜面数基本成线性规律,面积利用率与无量纲跨度与接收器高度的比值μ/ξ有关。因玻璃镜面安装彼此之间存有间隙,可大大降低风阻；由于采用平面玻璃镜反射太阳辐射,在焦平面位置可以得到均匀分布的能流密度,提高光伏电池效率。其次,建立了线性菲涅耳玻璃镜面反射聚光器实验系统。用CCD法对聚光光强分布进行了测试,结果表明其分布均匀,与理论分析计算结果一致。采用单晶硅电池进行了聚光光伏发电实验,效率可以达到15.9%,具有较高的发电效率。过对单管集热器、双管集热器以及双管加扭转叶片集热器进行了聚光集热实验,分析了东西向线聚焦系统端头效应对集热的影响。结果表明集热温度在120℃以下时,该聚光系统的总体集热效率可以达到0.74左右,并且由于辐射热损的影响集热效率随集热温度的上升而减小。再次,在线性菲涅耳聚光反射太阳能聚光器的基础上,提出了一种聚光分频光伏光热综合利用系统。其中分频器选用Si02和Nb203作为高低折射率材料,使用Needle法针对单晶硅电池特性对其膜系结构进行了优化设计,结果显示,约80%的有利于单晶硅电池发电的光谱辐射(波长范围0.35μrn<λ≤1.1μm)可以透过涂层照射到电池表面,约71%不利于单晶硅电池发电的光谱辐射(1.1μm<λ≤3μm)被反射到了集热管上。从而大大降低了太阳电池的废热负荷。理论分析结果显示,对于单晶硅光伏电池宽度100mm,安放高度2000mm,角度360,聚光器理论聚光比56.8的聚光分频系统,单晶硅光伏电池发电效率可达11.99%,同时集热部分可以独立获得1511.4W/m的中高温热能。最后,提出了一种新型的分段式槽式太阳能聚光器,通过在平面框架上放置同焦线的多块抛物面反射镜面,将光线聚集于焦线处,使用平板型集热器或圆柱型集热器作为接收体,用于太阳能聚光光热利用。该聚光器由于采用分段式的抛物反射镜,因此相比传统槽式聚光器具有较小的风阻,较低的镜面高度,并同时能够达到较高的聚光倍数。根据几何光学原理给出了确定每块抛物镜面尺寸及位置的曲线方程,并根据各器件实测的光学性质对聚光器进行了理论分析计算,分析结果当聚光器跨度在4m以内时,接收器安装高度值应取1.2m以上,跨度在6m以内时,接收器安装高度值应取1.8m以上。理论集热效率可以达到0.75以上。更多还原

【Abstract】 At present, fossil energy source which is necessary for human’s survival and development is facing serious problems:the first is the limitation of fossil fuel reserves and non-renewable; the second are the serious environmental problems caused by fossil fuels such as greenhouse effect, air pollution and etc. Therefore, the development and utilization of renewable energy resources is very important and emergency. Solar energy is inexhaustible, clean and renewable, has captured more and more attention in recent years. However, the density of solar radiation is very low, which is the main disadvantage for its application. Developing a solar concentrator with low cost, high efficiency and stability is the most promising approach to improve the density of solar radiation and can promote the utilization of solar energy. Traditional solar concentrators in the form of trough, dish or tower exist certain defects in manufacture, installation and maintain, or the uniformity of the concentrated solar energy. On the basis of the traditional one, this thesis proposed a new linear fresnel reflector solar concentrator, a hybrid solar concentrating Photovoltaic/Thermal (CPV/T) system with beam splitting technique, and a segmented parabolic trough solar concentrator. The related theoretical and experimental works were carried out by the support of the National Basic Research Program of China ("973" Program)(Grant No.2010CB227305) and the CAS Solar Energy Action Program (Grant No. CX2090130012).Firstly, the construction and the design principle of the new linear fresnel reflector solar concentrator were proposed. This concentrator contains three parts: reflective glass mirrors, flat frame and concentrated solar receiver. The specified width and slope angle of each mirror are determined by its position, the width and the slope angle of solar receiver, and the solar cone. A dimensionless model was developed for the performance analysis of the concentrating system. According to the results of numerical analysis, it is found that the theoretical concentration ratio and the area utilization ratio are mainly related with the installation height of the receiver and the size of the flat frame. For a flat-panel receiver, its installation angle has a neglectable effect on the theoretical concentration ratio and the area utilization ratio. For a cylinder receiver, the theoretical concentration ratio is linear with the number of the mirrors, and the area utilization ratio is related with the ratio of the dimensionless frame size and receiver height μ/ξ Because of the gaps between the glass mirrors, the wind drag is greatly reduced. Due to using flat glass mirrors, uniform energy flux density can be generated on the focal plane, which can improve the efficiency of photovoltaic generation.Secondly, an experimental system of the proposed linear fresnel reflector solar concentrator was developed. The distribution of concentrated solar radiation of the focal plane was measured by using CCD method, and the results show a high uniformity of the flux distribution and agree well with the theoretical simulation results. The CPV experiments were carried out, and the results show that the monocrystalline silicon cell can achieve a high PV generation efficiency of15.9%. The concentrating solar thermal experiments were also investigated for single-tube receiver, double-tube receiver and double-tube receiver with twisted blades. The end effect of the east-west linear concentrating system was analyzed. The experimental thermal efficiency of the system can achieve about0.73～0.74when the operation temperature is under120℃, and decreases with the increasing of the operation temperature because of the radiation loss of the receiver.Thirdly, a hybrid solar concentrating PV/thermal (CPV/T) system with beam splitting technique was proposed based on the linear fresnel reflector solar concentrator. SiO2and Nb2O3were employed as the high and the low refractive index materials for the beam splitter, and the selectivity transmission coating was designed and optimized for monocrystalline silicon cell by Needle method. The results show that nearly80%of the desired radiation for monocrystalline silicon solar cell (0.35μm<λ≤1.1μm) is transmitted to the solar cells, and about71%of the undesired radiation (1.1μm<λ≤3μm) is reflected to the thermal receiver for thermal utilization. Thus, the waste heat load of solar cells would be much reduced. For a CPV/T system with concentration ratio of56.8, cells width of10cm, cells height of200cm, and cells slope angle of36°, the theoretical PV generation efficiency is11.99%, and and thermal energy of1511.4W per meter length can be simultaneously harvested with high temperature.Finally, a novel segmented parabolic trough solar concentrator was presented, in which several segmented parabolic mirror reflectors with the same focal line were fixed to a flat frame. It can generate a concentrated radiation on a flat panel solar thermal collector or a tube solar thermal collector, which covert solar energy into thermal energy. Compared to the traditional parabolic trough concentrator, the proposed concentrator has a lower wind resistance and a lower mirror height because of the segmented parabolic mirrors, and also can reach a similar high concentration ratio. The parabola formulas of mirror reflectors were derived to determine their sizes and positions based on the principle of geometrical optics. According to the experimental results of every components of the concentrator, the theoretical performance of the segmented parabolic trough solar concentrator was investigated and analyzed. The results showed that the receiver height should be over1.2m for concentrator aperture within4m, and over1.8m for concentrator aperture within6m. The theoretical thermal efficiency is over0.75.更多还原