【作者】 刘可亮；

【导师】 季杰；

【作者基本信息】 中国科学技术大学 ， 热能工程， 2007， 博士

【摘要】 光伏电池的转换效率随着工作温度的升高而下降，这常常会导致光伏电池在无冷却的条件下效率较低。为了降低光伏电池的工作温度，利用这部分热量，并同时提高太阳能的利用率，对太阳能进行光电、光热综合利用是一个很好的选择，近年来这方面的研究在国内外得以逐渐展开。参阅相关文献可以发现：光电／光热综合利用的研究主要有以下两种方式：一种是利用水作为冷却介质，被加热后用来作为生活用水，或者作为热泵系统的辅助热源；另一种是利用空气作为冷却介质，加热后的空气被导入到室内给房间采暖或进行其它形式的再利用。相关的研究表明：采取了上述冷却措施后，光伏电池的效率得以明显改善，同时太阳能的综合利用率也得以显著提高。然而为了使水或空气可以达到直接利用或再利用的目的，常常希望冷却介质的能达到较高的温度，这和提高光伏电池效率的方向是背道而驰的。为了从根本上解决这个问题，我们提出了一种新型的太阳能综合利用方案：即把光伏集热器和热泵系统直接偶合起来，利用温度较低的制冷剂带走光伏集热器的热量，由此可以达到很好的冷却效果，并可以在热泵的冷凝端输出品质提升后的热量用于采暖或制取生活用热水。这种系统被称为光伏太阳能热泵(photovoltaicsolar assisted heat pump，PV-SAHP)，对其进行的相关研究表明该系统具有优良的热性能，并且光伏电池的转换效率也得以显著提高。本文利用分布参数模型对光伏太阳能热泵系统的核心部件—光伏蒸发器进行了深入的数值研究，并在此基础上构件了PV-SAHP系统模型，研究了结构参数、太阳辐射强度、环境参数等因素的改变对光伏蒸发器和整个热泵系统性能的影响。对光伏蒸发器的模拟采用了分布参数法，相对于集总参数法而言，这种方法具有更高的精度。它能够给出光伏蒸发器各绢件的温度分布以及能量流动特点，并同时给出光伏蒸发器的热／电输出等。在上述理论模拟的基础上，设计并搭建了光伏太阳能热泵实验台。并在合肥冬季的气候条件下，进行了相关的实验研究。对实验结果和数值模拟结果进行了对比分析，二者具有很高的一致性，验证了所建模型具有较高的精度。研究结果表明光伏蒸发器的热效率可以达到0．53～0．75：电效率可以达到0．124～0．135；综合效率可达到0．64～0．87，与同类型的集热器相比高出约10％以上。光伏太阳能热泵的COP最高达到8．4，平均COP为6．5。由此可见光伏太阳能热泵具有非常优越的性能。采用上述模型，本文还对光伏太阳能热泵的变频率工作特性进行了数值模拟研究。由于光伏太阳能热泵是工作在宽幅变动的太阳辐射和环境温度下，因此必须对制冷剂流量进行适时调整，以避免蒸发器山口的制冷剂处于两相状态，危及到压缩机的安全运行，或者蒸发器出口制冷剂的过热度太大，导致散热损失增加，降低蒸发器的热效率。本文采用了变频率和电子膨胀阀的二级调整方式调节制冷剂流量，使其与外界参数的变化相匹配，取得了很好的效果，使光伏太阳能热泵系统处于安全、高效的运行状态。更多还原

【Abstract】 Photovoltaic efficiency declined with the increase of the working temperature. This leads to a relatively lower efficiency when solar cells operating without a cooling service. In order to utilize this part of thermal energy, which was discharged to the environment directly, a comprehensive utilization of the solar energy is a good alternative. Researches on this field have been widely carried on inside and outside china.References revealed two main modes were adopted by various authors in photovoltaic/photothermic (PV/T) utilization of the solar energy: in the first mode water was used as the coolant of the PV panels and the heated water was used for domestic usage or as a thermal resource of a heat pump. In the second mode air was used as the coolant, and the hot air was inducted to a room for space heating. The results demonstrated the photovoltaic efficiency was improved with the cooling effect, and the overall efficiency was also lifted to a higher level.However the water or air was usually heated to a relatively high temperature on the purpose of a direct usage. This was on the opposite direction of the photovoltaic efficiency improvement. This paper proposed a novel system which was directly coupled of a PV solar collector and a heat pump. The solar collector acted as the evaporator of the heat pump. In the evaporator, refrigerant absorbed heat from the PV base plate, and discharged it to the cooling water in the condenser. In this way the PV panel’s temperature dropped and the photovoltaic efficiency was improved at the same time. This novel system was named as photovoltaic solar assisted heat pump (PV-SAHP). Research has revealed it has a superior thermal and electrical performance.A distributed parameters approach has been successfully used to simulate the PV evaporator. On this base, the model of the PV-SAHP system was also built. Researches were focused on the structural parameters and environmental parameters, which influenced the performance of the heat pump. Compared to the lumped parameters approach, the distributed parameters approach has a higher accuracy. It can give the temperature distribution of the refrigerant along the tube, and calculate the thermal /electrical outputs at the same time.Based on the above theories we designed and built the experimental rigs of the PV-SAHP system. Experimental researches were taken under winter weather conditions of Hefei region. The results of the experiment and simulation agreed very well, which demonstrated the system’s model has a high accuracy. The thermal efficiency, electricity efficiency and the overall efficiency of the PV evaporator were G.53～0.75, 0.124～0.135, and 0.64～0.87 respectively. Compared to a water-based or air-based PV/T collector the overall efficiency was 10% higher. The coefficient of performance (COP) reached 8.4 with an average value of 6.5, which demonstrated the PV-SAHP system has a superior performance.With the models above, this paper also give a numerical study of the PV-SAHP system working in a variable frequency condition. When PV-SAHP operates, the solar radiation intensity and ambient temperature varied in a wide range, so it is necessary to adjust the mass flow rate of the refrigerant according to the environment parameters. This can effectively avoid two-phase flow appears at the outlet of the evaporator, or control the superheated degree of the refrigerant within a suitable region. If the two-phase flow flushed into the compressor, the compressor would be seriously damaged. If the superheated degree is too high, the heat loss to the environment increased and the thermal efficiency of the evaporator dropped on the contrary. This paper adopted a two-stage modulation through the compressor frequency and the expansion valve to match the mass flow rate with the thermal load, which ensured the PV-SAHP system working in a healthy, effective state.更多还原