【作者】 茆磊；

【导师】 夏维东； 叶宏；

【作者基本信息】 中国科学技术大学 ， 热能工程， 2010， 博士

【摘要】 热光伏(TPV)系统是目前最先进的分布式能源解决方案之一,它利用光伏(PV)电池将人造热源的热辐射能转换为电能输出,故其基本原理与PV系统完全相同,即利用半导体PN结的光电转换特性。由于人造热源辐射距离小,TPV系统拥有比PV系统高得多的输出电功率密度,可达数瓦每平方厘米,并且输出稳定,不受天气等因素影响,这是TPV系统最为显著的特点之一。TPV系统的其它优势和特点还包括：可应用能源形式多样,运行安静、维护成本低,安全、无污染,可实行热电联供等。上述优势和特点决定了TPV系统在工业、商业、军事和航空航天等领域都将拥有非常巨大的实用价值和应用前景。TPV系统的主要构成部件为热源、辐射器、TPV电池、光子回收系统和能量控制单元。热源提供系统所需的辐射能量,其形式多样,包括化学燃料燃烧能、核能、太阳能等。辐射器将热源的能量辐射至TPV电池表面,分为灰体辐射器和选择性辐射器。TPV电池将接收到的辐射能转化为电能输出,是TPV系统的核心部件,决定了TPV系统的性能水平。光子回收系统用于回收半导体能带外的光子,以降低能量损耗,包括前置滤波器和背面反射器(及其组合)。能量控制单元控制系统的电能输出、各部件的冷却和余热回收等。目前对于TPV的研究主要围绕以上各关键技术以及系统构建展开。辐射器、TPV电池和光子回收系统是TPV系统的关键部件,它们一起构成了TPV系统的核心——热辐射发电模块。在热光伏系统性能初步研究中,建立了该模块的数学物理模型,通过数值模拟获得了SiC灰体辐射器分别配合GaSb和Si电池所构成的TPV系统的输出伏安特性曲线；再以GaSb电池为例,分别分析了SiC灰体辐射器温度、电池温度对系统性能的影响。得出结论：辐射器温度升高,系统输出电功率密度迅速增大,电池效率也稳步提高；电池温度升高则导致系统性能下降,电池效率也大幅下降。最后,讨论了与GaSb匹配的一种选择性辐射器的辐射能量分布情况。与SiC灰体辐射器相比,选择性辐射器可以显著减少辐射能量中的不可用部分,从而有效提高系统的性能。TPV系统的光谱控制部件包括选择性辐射器和光子回收系统。光谱控制部件对于提高光谱效率乃至TPV系统效率具有举足轻重的作用,是构建高性能TPV系统的关键部件之一。本文从配合以GaSb电池为转换器的TPV系统的滤波器入手,分别对透明导电氧化物(TCOs)滤波器和一维Si／SiO2光子晶体滤波器进行了理论和实验研究。在透明导电氧化物滤波器的优化分析中,建立了TCOs滤波器的理论模型,分析了载流子浓度、迁移率等电学参数对其光学性能的影响；计算了辐射器种类分别为A1203／Er3Al5012熔融陶瓷选择性辐射器和SiC灰体辐射器、而辐射器温度为1 400～1 600 K时,应用于以GaSb电池为转换器的TPV系统的TCOs滤波器的最佳载流子浓度和薄膜厚度区间。最后,讨论了石英玻璃衬底厚度对TCOs滤波器性能的影响,并考察了A1203／Er3Al5O12熔融陶瓷选择性辐射器+TCOs滤波器+GaSb电池的TPV系统的性能。针对一维硅／二-氧化硅光子晶体滤波器,建立了一维Si／SiO2光子晶体滤波器的理论模型,并指出原始结构的(L／2HL／2)5型光子晶体滤波器在GaSb电池特征波长处存在较大反射峰,制约了TPV系统性能的提高；再根据对称单元的等效折射率理论,将其结构改进为[1.10(L／2HL／2)](L／2HL／2)3[1.10(L／2HL／2)],即中间三个单元不变,左、右各最外一个单元修改为折射率匹配单元。模拟结果表明：改进型滤波器在特征波长处的透过率有较大改善,且一定程度地抑制了长波光子的透过；辐射器为1250℃的黑体时,采用改进型滤波器光谱效率和输出电功率密度均提高10%以上,电池效率也有所提高。采用磁控溅射方法制作了原始结构和改进型一维Si／SiO2光子晶体滤波器的试样,试样截面电镜图像表明所得光子晶体滤波器试样结构与设计大致相符,试样的光谱反射率和透过率的测量结果与数值模拟结果吻合良好。在辐射热阻网络法热光伏系统热分析中,采用辐射热阻网络方法建立了LMFraas提出的典型中温TPV系统的辐射换热模型。相对于蒙特卡罗等方法,辐射热阻网络法的优势是模型较简单,计算量小。但对模型的一般求解过程中并未考虑石英玻璃管对辐射光子的波长转换作用,导致计算所得的石英玻璃管的光谱发射功率密度与普朗克定律相违背。通过在辐射热阻网络中添加虚拟的单色波热源的方式对模型进行了修正。该方式忽略了波长转换的详细过程,可以简化修正模型的复杂程度,并减少计算量和计算时间。采用修正模型得到了系统的辐射热流密度、光谱效率和石英玻璃管的等效辐射温度等一些重要参数,与参考文献中蒙特卡罗等复杂模型的结果吻合较好。更多还原

【Abstract】 As one of the most advanced power solutions presently, thermophotovoltaic (TPV) system converts thermal radiation from man-made heat source into electricity by photovoltaic (PV) cell. It utilizes the same principle as do PV system, namely the photoelectric effect of semiconductor. Due to the small distance of the man-made heat source, the power-density output of the TPV system is much higher than the PV system, approaching a few Watt/cm2, stably without being affected by any weather condition. This is the most significant advantage of TPV system. Other advantages include versatile fuel-usage, quiet operation, low maintenance, safe, pollution free and possibility for cogeneration of electricity and heat. All those make the TPV applications in the field of industry, commerce, military and aerospace very promising and attractive.A TPV device consists of a heat source, a radiator (emitter), a TPV cell array, a photon-recycle system and an energy-management unit. The heat source, which provides the necessary radiation energy, can be the fuel combustion, nuclear or solar energy. The radiator, which radiative the energy from the heat source towards the TPV cells includes gray-body radiator and selective radiator. The TPV cells, which converts the received radiation into electricity outputs, is the pivotal component of the system and therefore dominates the system performance. The photon-recycle system, which recycles out-band photons to reduce the energy waste, can be classified into two categories, the front filter and backside reflector (or the combination of both). The energy-management unit controls the output, cooling and waste-heat recovery of the system. Present researches mainly focus on the advance technology of those separate components and the demonstration of system prototypes.The key components of the TPV system are the radiator, the TPV cells and the photon-recycle system, which compose the core of the system, namely the thermal radiation-electricity module. In the primary investigation research on the TPV system performance, physical and numerical model of this module is constructed. Current/voltage characteristics of the system consisting of a SiC gray-body emitter and GaSb or Si PV cells are obtained. Influences of the emitter temperature and the cell temperatures on the performance of the system consisting of a SiC emitter with GaSb cells are analyzed, respectively. The power-density output as well as the cell efficiency increases with the emitter temperature. However, the rise of the cell temperature leads to negative effects. Whereafter, the radiative energy distribution of a selective emitter matching GaSb cell is discussed. The selective emitter cuts down the unusable radiative energy remarkably comparing with a SiC emitter, and thus improves the system performance significantly.In the TPV system, the selective radiator and the photon-recycle system are so called spectral-control components, which decide the spectral efficiency of the system and further contributes to the system efficiency. Considering that the spectral-control components are the very key components for high-performance systems, this paper presents a detailed theoretical and experimental discussions on the transparent conducting oxides (TCOs) as well as one dimensional (1D) Si/SiO2 photonic crystal (PhC) filter matching TPV systems based on GaSb converter.In the analysis and optimization of TCOs filter, the model of TCOs filter is constructed and the influence of the carrier concentration as well as mobility on the spectral properties is analyzed. The optimal carrier concentration and film thickness are evaluated for TPV system based on GaSb converter with Al2O3/Er3Al3O12 eutectic ceramic selective radiator as well as SiC gray-body radiator varying from 1400 K to 1600 K. At last, the influence of the quartz thickness on the filter properties is discussed, and the performance of the system consisting of the Al2O3/Er3Al5O12 selective radiator, the TCOs filter and GaSb cells is investigated.In the development of 1D Si/SiO2 PhC filter, the theoretical model of 1D Si/SiO2 PC filter is constructed, and the issue that large oscillations around the characteristic wavelength of GaSb cell in the pass band of 1D PhC filter of (L/2HL/2)5 structure leads to a discount on the system performance is pointed out. A modified 1D Si/SiO2 PhC filter of [1.10(L/2HL/2)](L/2HL/2)3[1.10(L/2HL/2)] is designed based on the theory of equivalent refractive of symmetry unit. In the modified structure, the 3 middle units remain unchanged while the left and right units serve as the refractive match units. Simulation results indicate that the transmittance around the characteristic wavelength of the modified PhC filter is improved remarkably and the transmission of long-wavelength photons are also inhibited. The spectral efficiency and power-density output of the system with a blackbody radiator at 1250℃can be improved 10% by adopting the modified 1D PhC filter comparing to the original 1D PhC filter, the cell efficiency is also improved at a certain extent. Both PhC filter samples of the modified and original structures were prepared through a magnetron sputtering process. The cross-section SEM indicates that the structures of the prepared samples approximately match the design and the measured spectral reflectance and transmittance show good coherence with the simulation.In the thermal analysis of TPV system using the radiation resistor network method, the radiative heat transfer model of a typical medium-temperature TPV reported by L M Fraas is constructed by adopting the radiation resistor network method, the advantages of which include simple modeling and short computation time comparing with the Monte Carlo (M-C) method. However, in the usual solving process no consideration of the wavelength-shift for the photons when passing the quartz envelop will lead to violation of the spectral emissive power density pf the quartz with the Planck’s Law. Whereafter, the model is improved by adopting a fictitious monochromatic heat source. This method ignores the detailed process of the wavelength shift, so it can predigest the complexity of the model and reduce the computation time. The calculated radiative heat flux, spectral efficiency and the equivalent radiative temperature of the quartz envelop from the improved model fit better with the results from M-C model in the literature.更多还原