An experimental study on the shading effects of Photovoltaic system

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An experimental study on the shading effects of Photovoltaic system


Author: Chik, Tsz-yan
Title: An experimental study on the shading effects of Photovoltaic system
Degree: M.Eng.
Year: 2006
Subject: Hong Kong Polytechnic University -- Dissertations
Photovoltaic power systems
Photovoltaic power generation
Department: Dept. of Building Services Engineering
Pages: xv, 106, [2] leaves : ill. (some col) ; 30 cm.
Abstract: Since a Photovoltaic (PV) system's power output decreases when it is shaded by surrounding buildings, it is important to investigate the influence of the shading on monocrystalline photovoltaic modules as well as building-integrated photovoltaic systems. With the utilization of laboratory test, the most important parameters, i.e. short-circuit current, open-circuit voltage, maximum power output and fill factor of PV modules were determined under various climatic conditions. In addition, the relationship between the decreased output due to the shading and the change of the I-V characteristics were examined. The findings suggest that the I-V characteristics are changed by the conditions of the shadow, which covered the module. A PV module tester, which complies with the requirements of the International Electrotechnical Commission (IEC) standard, was set up to experimentally study the characteristics of monocrystalline PV module. The dissimilarity between nominal parameters of manufacturer's specification and experimental results measured from the PV module test was only ± 8.5%. These results have proved that the PV module tester is a suitable tool in the PV market as well as in the PV power generation industry for academic research purposes.
The mathematical model, based on the concept of a diode model was used in which five parameters were determined by experimental results. A good agreement was found by using this mathematical model to simulate the actual performance of BIPV system. Furthermore, the stimulation results obtained from the software ECOTECT indicate that the neighboring building Li Ka Shing Tower blocked direct sunlight exposed on the PV panel in some specific periods of the year. Therefore, an assessment of yield reduction due to shadowing effect was carried out, using the mathematical model and theoretical calculations. The results indicate that the average energy yield was reduced by about 23% during a daytime between 7:00 am and 11:00 am for both typical sunny and cloudy days. By taking site measurements, it is concluded that the influence of solar intensity on the energy performance of the tilted PV was significant and the overall system efficiencies of two typical days were almost the same, about 5% in average. It would appear that the system loss primarily occurred in conversion from solar energy to electricity and secondarily in inverter and wiring losses. The inverter efficiencies also fluctuated with a constant range, with average of 90%.

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