Abstract:

The unglazed PV/T system with full photovoltaic coverage has a simple structure and excellent electrical performance, but its thermal efficiency is low and the study on its energy loss is rare. In this paper, based on the first and second laws of thermodynamics, the energy balance equations of unglazed PV/T were established respectively, and an experimental platform was built to carry out the performance test under different temperatures and flow conditions. The cooling effect of working medium was verified by combining the temperature curve of the PV cell, and the thermodynamic characteristics of the system was analyzed from the perspective of enthalpy-entropy-exergy. It was found that the water-cooled channel improves the efficiency of photovoltaic modules and the uniformity of the temperature field, and shortening the water heat collection time contributes to energy saving and revenue. Ambient temperature was an important factor affecting the thermal efficiency, thermal exergy efficiency and heat loss rate of PV/T system, while the electrical efficiency was more obviously affected by the flow rate. Under the test conditions, the maximum electrical, thermal, and comprehensive efficiencies of the unglazed PV/T system were 17.36%, 25.37%, and 70.12%, respectively. The high electrical efficiency ensures the quality of energy collection, and the water collection temperature could be adjusted by the flow to meet the needs of life. Increasing the flow rate could improve the exergy efficiency of the PV/T, and the optimization plan involving the pump can further improve the economy of the system. The increase of system entropy was negatively correlated with the exergic efficiency, and it showed a decreasing trend with the increase of flow rate. The data showed that the exergy efficiency of the PV/T system reached the maximum value of 19.05% when the flow rate was 0.06kg/s, corresponding to a minimum entropy of 0.0191kW·h/K.

Key words: solar energy, PV/T, enthalpy, entropy, exergy, thermodynamics, energy loss

摘要：

光伏全覆盖的无盖板光伏/热（PV/T）系统结构简单，电性能优异而热效率偏低，有关其能量损失的研究还少有涉及。本文基于热力学第一、第二定律分别建立无盖板PV/T的能量平衡方程，搭建实验平台开展系统在不同温度、流量工况下的性能测试，结合电池温度曲线验证工质的冷却效果，并从焓-熵-?的角度对系统的热力学特性进行分析。研究发现，水冷通道提升了光伏组件的效率和温度场的均匀性，同时缩短水集热过程的时间将有助于系统节能和增加能量收益；环境温度是影响PV/T系统热效率、热?效率以及热损失率的重要因素，电效率则受流量变化的影响更为明显。测试条件下，无盖板PV/T系统的电、热、综合效率的最大值分别为17.36%、25.37%、70.12%，较高的电效率保证了能量收集的品质，而热水收集温度可以通过调节流量大小以满足生活需求。增大流量能够提高PV/T系统的?效率，结合水泵运行的优化方案可进一步提升系统的经济性；系统熵增与?效率呈负相关性，随流量的增大呈降低的趋势。数据显示，流量0.06kg/s时PV/T的?效率达到最大值19.05%，对应的熵为最小值0.0191kW·h/K。

关键词: 太阳能, 光伏/热, 焓, 熵, ?, 热力学, 能量损失