| 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. |
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