Characterization And Evaluation For Safety And Thermal Performance Of Photovoltaic Glass

Failures of photovoltaic glass, such as spontaneous breakage of tempered glass and delamination laminated glass affect the PV modules safety and service life.Coupled with the development trend of thin and lightweight PV module and Building Integrated Photovoltaic(BIPV) energy-saving requirements, evaluation and characterization of structural safety and energy-saving performance of PV glass needs to be established. Theoretical studies of mechanical and thermal properties of typical PV glass were accomplished and some new test methods and test facilities were developed in this thesis.(1) The function of the internal stress of tempered glass was established and then the relationships between the thicknesses of the tensile stress layer and compressive stress layer was derived. The cause of spontaneous breakage of tempered glass is due to the stress concentration in the tensile stress layer. Tempered glass with higher stress has more break probability and the probability of spontaneous breakage is proportional to the cubical size of impurities radius. The closer to the neutral layer, the spontaneous breakage happens easier. In addition, working temperature changes or asymmetric temperature distribution can also lead to spontaneous breakage. Based on the principle of photo-elastic, inspection apparatus for detecting spontaneous breakage defects of tempered glass were developed which can rapidly detect and identify the spontaneous breakage defects of PV tempered glass.(2) Based on the "mean strength criterion" theory, the effect of stress gradient on the bending strength of glass was studied which explained the relationship between the bending strength and thickness of the thin glass. Equivalent Coating Method(ECM) is presented by adopting the bending model with small deflection and low stress gradient for testing bending strength of thin and ultra-thin glass which can accurately determine the fracture strength of thin and ultra-thin glass. A cantilever beam transient excitation method was used to measure and calculate the elastic modulus of ultra-thin glass. The elastic modulus of ultra-thin PV glass could be calculated simply by using the natural frequencies of the cantilever beam with Length-thickness Ratio(LTR)≥10.(3) “Double cross-section” method for determining interface bond strength of laminated glass is established which provides a precise test technology for evaluating the brittle material interface bonding strength. On the basis of this method, the tension bonding strength and shear strength of PV laminated glass with EVA and PVB film respectively were studied under damp-heat exposure and natural atmospheric exposure. The results show that EVA is more sensitive to the damp-heat aging and atmospheric environment than PVB and its performance decline ratio is greater than PVB film with the increase of the aging period.(4) Three kinds of efficient numerical calculation methods of temperature field response of PV laminated glass with uncertain parameters are developed. By retaining some high-order terms of Neumann series, the high-order perturbation method can effectively improve the computational accuracy. The sub-interval perturbation method is more suitable to the heat transfer problem with large uncertain parameters by the sub-interval decomposition technology. Interval collocation analysis method has higher calculation precision in solving the upper and lower bounds of temperature by adopting the finite order Chebyshev polynomial series to express interval system temperature response.(5) Based on the analysis of the heat transfer mechanism of PV laminated glass,the solar heat gain model was established and the heat transfer formula was derived. A new indicator defined as "Solar Heat Gain-Electric Energy Outputs Ratio(HEratio)” of PV glass was proposed to characterize the relationship between solar heat gain and power generation. Furthermore, a test system for measuring the solar heat gain of PV glass was developed. Experimental results of solar heat gain of three typical PV glass show that the solar heat gain capacity of PV glass is affected by installation angle, PV glass structure and cell area ratio. The heat gain will decrease effectively following with the increase of solar cell area.