【作者】 秦红；

【导师】 张仁元； 沈辉；

【作者基本信息】 广东工业大学 ， 材料学， 2011， 博士

【摘要】 开发可再生能源与发展低碳经济已成为当前世界各国应对能源可持续性发展和环境问题的共识。太阳能光伏发电无疑是可再生能源中最受瞩目最有发展前景的技术,许多专家预言,21世纪中叶,光伏发电将占世界总发电量的15%～20%左右,成为人类的基础能源之一。进一步提高太阳电池效率,降低光伏发电成本是发展太阳能光伏并逐步提高其在整个能源中的比例的根本关键。太阳电池工作时未转换为电能的太阳能将转换为热能并储集在组件系统内,导致太阳电池工作温度升高,而太阳电池效率随温升近似直线下降。以提高光电转换效率为目的的太阳电池冷却研究随之兴起。大量研究证明冷却可提高太阳电池效率,但详细的机理涉及不多。目前的太阳电池冷却技术有水冷与风冷两大类别,最终都以大气为低温热源,其冷却终了温度总是高于即时气温。而即时气温随太阳辐射强度增大而升高,致使太阳辐射越强烈,效率反而下降,成为提高冷却效果的热力学瓶颈。本课题针对太阳电池冷却研究背景和传统冷却技术的不足,在广泛查阅文献资料,分析太阳电池冷却技术现状的基础上,将材料学与工程热物理相结合,微观粒子动力学研究与宏观系统研究相结合,理论分析与试验测试相结合,对太阳电池冷却机理和系统的强化传热过程和应用性能进行了深入研究。主要研究工作与结论包括以下几个方面：1.温度对太阳电池效率的影响机理分析从太阳光与电池材料作用的内部电子过程出发,明确太阳光照射下硅太阳电池的电子-空穴对形成过程、电子输运过程和收集过程中温度影响的机理与具体形式,以及温度降低对太阳电池效率提高的贡献率分析方法。太阳电池性能对温度十分敏感,从机理分析出发,主要是温度对禁带宽度的影响,对载流子运动速度的影响和对散射三个方面的影响。论文分析得出两点重要结论：(1)降低太阳电池工作温度对于太阳电池效率提高的贡献,主要在于减少载流子迁移途中的能量损失,从而在入射太阳辐射能量相同的条件下提高载流子输出比例,即提高太阳电池效率。(2)降低太阳电池工作温度对于太阳电池效率提高的贡献,与温度降低近似成线性比例。但只有降温不需耗用能源或耗用能源甚少时,对于系统的能效贡献才是有效的。2.太阳电池组件的热力学与传热学分析对太阳—太阳电池组件—大气环境形成的热力系统运用能量守恒定律,分析太阳电池工作过程中光—电—热转换的具体过程,明确了组件内温度分布、影响因素及其变动规律,以及对光电转换的影响。研究表明,在一定的太阳电池材料与组件结构形式下,太阳电池的温度及效率随太阳辐照度与环境温度作近似线性变化,而变化率决定于太阳电池组件材料的物理和热力学性能参数,以及组件结构与表面传热系数。常规平板式太阳电池组件中,太阳电池处于温度最高点,所能取得的最低温度为大气温度,且只能在太阳辐射为零的条件下取得。研究发现：当前太阳电池组件材料与结构下,太阳电池组件内部热阻太大,导致表面放热系数对于传热的影响减小。因此降低太阳电池组件材料的热阻,加大太阳电池冷却的温差成为重要的任务。3.金属背板太阳电池组件的研究以减小太阳电池组件热阻为目标,研究了改变背板材料对于太阳电池组件性能的影响。通过封装材料选择原则和方法的研究,以金属材料代替高热阻的高分子材料作组件背板,从光学、机械学、热学、化学、电学及经济学方面综合匹配,进行材料种类和规格、强度、腐蚀性、绝缘性、传热性能、表面性能以及热伸长方面的的分析处理,特别是用机械方法减小材料伸长量不匹配对太阳电池的应力影响,以及保证绝缘要求的同时降低高分子材料对于导热的影响,开发出新型铝合金背板太阳电池组件,获得了授权发明专利。经试制实验研究,确认在广州同一环境条件下,铝合金背板太阳电池组件与TPT背板太阳电池组件相比,背板温度降低2-8℃,最大功率增加2%以上,且效果随太阳辐照度增加而上升。4.蓄冷降温式太阳电池组件的研究以不耗或少耗能源的前提下加大太阳电池冷却的温差为目标,研究提出了将大气温差能与太阳能结合,来改变太阳电池组件散热的低温热源,形成多热源的散热环境的创新性思路。通过对环境大气温度变化规律、系统能量传递和转换过程的各个环节与参数及强化传热结构的优化研究,构建出将大气自然温差冷能转移到白天,用于冷却太阳电池的原始创新性的蓄冷降温式太阳电池组件复合系统,提出了蓄冷降温式太阳电池组件原理与设计方法的完整论述,突破了常规冷却的低温热源温度瓶颈,大大降低了太阳电池组件温度,获得了授权发明专利。经开发试制实验研究,确认在广州同一环境条件下,蓄冷降温式太阳电池组件与对照组TPT背板太阳电池组件相比,背板温度最大可降低26.5℃以上,最大功率增加可达14%～18%。更多还原

【Abstract】 With the development of renewable energy and low carbon economy, new energy technologies have become the consensuses about dealing with sustainable energy and environmental issues. Solar photovoltaic is the most attractive and promising technology in all kinds of renewable energy technology. The global solar photovoltaic power generation will account for 15% to 20% of the number as one of the basic energy in the world in middle of 21st century. Improvement efficiency of solar cell and reduction cost of photovoltaic power generation are the keys to develop solar photovoltaic technology and increase its proportion in the whole energy resources gradually.When solar cells work, part of solar energy not converted into electricity are transformed into heat and reserved in photovoltaic module. That will result in linear reduction of conversion efficiency with raise of temperature of module. The researches of PV’s cooling technology spring up in order to improve photovoltaic conversion efficiency of solar cells. Although a large number of researches proved that reduction temperature of solar cells can increase its efficiency, few of them concerned with the detailed mechanism. The current solar cell cooling technologies include two categories: water cooling and air cooling both using air as the low temperature heat source which results in final temperature higher than the transient air temperature. Therefore, as the transient air temperature increase with the solar radiation intensity, the intense solar radiation will lead to decrease of the efficiency. This problem has become a bottleneck in improving the cooling performance.According to the background of solar cells’cooling research and the defects of traditional cooling technology, and based on the review of extensive literature and analysis for latest solar cells’cooling technology, the solar cooling mechanism, the course of the system’s enhanced heat transfer process and working performance of solar cell is researched in-depth by uniting material science and Engineering Thermophysics, microparticle dynamics and macrosystem, theoretical analysis and experimental and numeral simulation. The main research works and conclusions are as followings:1. Mechanism of temperature effect on the solar cells’ efficiencyBased on the internal electronic process between sunlight and the material in cells, the mechanism of temperature effects and its specific acting forms are defined in the processes of electron-hole pair formation, electron transport and collection occuring in silicon solar cells. The method in analysis the contribution rate of temperature decrease which brings about the increase in efficiency of solar cell is also cleared. Due to the performances of solar cell is strongly sensitive to temperature, mechanism analysis mainly includes the following three parts:the effects of temperature on forbidden energy gap; the effects of temperature on carriers’ velocity and the effects of temperature on scattering. Two important conclusions are drawn:(1) Increase in solar cells’ conversion efficiency is mainly due to the energy loss decrease in carriers’ transport process when the temperature drops, so carriers’output proportion and solar cells’ conversion efficiency are both improved in the same solar radiation intensity. (2) The efficiency and output of solar cell linearly increase when the temperature decrease, but it is effective for system efficiency only in case of no energy consumed or less energy consumed.2. Thermodynamics and heat transfer analysis of the solar photovoltaic modulesThe energy conservation law in the heat system formed by the sun, solar photovoltaic module and atmosphere are used to analyze the specific light-heat-power process. The temperature distributions in module, its influence factors and principle of factors’changes were determined, and these effects on photoelectric conversion are also obtained. When material of a solar cell and module structure were confirmed, the solar cell’s temperature and conversion efficiency almost changes linearly with solar radiation and air temperature’s variation, and the change rate depends not only on the physical and thermodynamic performance parameters of the materials and its structure configuration, but also on the surface shape and surface heat transfer coefficient. For the conventional flat-plate modules, the highest temperature appears in solar cell, and its lowest temperature equals to the air temperature only observes when solar radiation is zero. It was found that under present material and structure of solar photovoltaic module the interior thermal resistance was extremely large that lowered the effect of exterior convective heat transfer coefficient on the heat transfer rate. Therefor both decreasing material thermal resistance of the module and increasing temperature difference in cooling become very important.3. Research on solar photovoltaic module’s metallic backplaneAimed at decreasing material thermal resistance of the module, the effects of various backplane materials on the solar photovoltaic module’s performances have been investigated. Based on the studies of the selection principles and methods, metal material was utilized as backplan Material to substitute high Polymer material through comprehensive match from optical, mechanical, thermal, chemical, electrical and the economical aspects. The material type and size, mechanical strength, corrosion resistance, insulation, heat transfer properties, surface properties and thermal elongation are analyzed and determined. A innovative mechanical method is proposed to reduce effects on the stress of cells caused by mismatch of material extension length, which not only guaranteed insulativity but also lowered the effect of high Polymer Material on heat conduction. A new type of solar modules used aluminum alloy backplane was developed and a convention patent has been authorized. The experimental studies confirm that the backplane temperature of the solar modules with aluminum alloy may decrease 2～8℃compared to TPT backplane solar modules in the same environmental condition of Guangzhou. The maximum power may also increase up to 2% while the effects would strengthen as the solar radiation increase.4. Researches on Cool-Sstorage Mode Solar Photovoltaic ModuleAimed at increasing cooling temperature difference based on no energy consumed or less energy consumed, a innovational concept and method were presented that atmosphere’s temperature difference and solar energy will be combined together to alter the low temperature heat release surrounding and create multi-source, and its influences on solar module’s performance was analyzed. Through the studies of atmospheric temperature variation and optimization both parameters of energy transfer and conversion and structures of enhanced heat transfer, a composite system named the Cool-Storage Mode Solar Photovoltaic Module(abbreviated as CSSM) was constructed, which diverts the atmosphere’s cold energy to day-time so as to lower the Photovoltaic module’s temperature. The principle and design method of CSSM are proposed, which breaks the temperature bottleneck of conventional cooling method, and greatly reduces the temperature of solar modules. This method also accesses to the authorized patents. The experiment studies confirmed that backplane’s temperature of CSSM may reduce the temperature by 26.5℃compared with TPT backplane Photovoltaic modules in the same environmental conditions at Guangzhou. A maximum output power increase up to 14%～18% were achieved.更多还原