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Title: Study on the overall energy performance of amorphous silicon based solar photovoltaic double-skin facade
Authors: Peng, Jinqing
Degree: Ph.D.
Issue Date: 2014
Abstract: Buildings have been consuming about 60% of the total electricity end-uses in Hong Kong and this proportion is increasing over recent years. Building facade, especially the glass curtain wall, as a key component of the building to connect the outdoors, affects the air-conditioning cooling/heating loads and lighting load significantly. Actually, it is one of the main sources of air-conditioning cooling/heating loads. Poor insulation performance of facade results in high cooling/heating energy use. Hence the need to develop energy efficiency facade is apparent. In this context, solar photovoltaic integrated double-skin facade (PV-DSF) technology has been attracting growing attention in recent years due to its improved thermal insulation performance as well as itself power generation ability. PV-DSF not only can significantly reduce the heat gain/loss via the building envelope, but also can generate electricity in situ through the photovoltaic effect. In addition, the use of semi-transparent amorphous silicon (a-Si) PV module in the PV-DSF not only increases the aesthetics of facade, but also make it possible to obtain more natural lighting so as to reduce lighting load. Although the semi-transparent PV-DSF is expected to be a promising energy efficiency facade, little research has been conducted on the long-term overall energy performance, in particular the dynamic power output performance under different weather conditions. Therefore, this thesis aims to investigate the overall energy performance including power generation performance, thermal and daylighting performances experimentally and numerically. To accurately predict the power performance, the impact of the solar spectral irradiance on the short circuit current of the PV-DSF was also studied thoroughly. Firstly, a novel ventilated PV-DSF based on semi-transparent amorphous silicon was developed outdoors. It mainly consisted of an outside layer of semi-transparent a-Si PV modules, an inner layer of an inward opening window as well as an air ventilation cavity between these two layers. This ventilation design can remove much of the waste heat generated by the PV module energy conversion processes, and thus bring down the operating temperature of the solar cells so as to improve its energy conversion efficiency. The long-term experimental results showed that the monthly average energy generation of the south-facing PV-DSF was about 3.3 kWh/m² in winter in Hong Kong. It could reduce the energy use of air-conditioning by 15% compared with the conventional double-skin facade. The average solar heat gain coefficient (SHGC) of the ventilated PV-DSF was about 0.15, which is much lower than that of a normal single glazing window. At noon on sunny days, the natural daylighting illuminance in the indoor room can reach up to 400 lux, which can meet lighting requirements for most of indoor activities.
As this PV-DSF can operate in different ventilation modes, such as natural ventilation, buoyancy-driven ventilation and non-ventilation modes, the thermal and power performances of PV-DSFs under different ventilation modes has been experimentally investigated to uncover appropriate operational strategies in different weather conditions to maximize its energy efficiency. The experimental results indicated that the naturally-ventilated PV-DSF gives a much better performance in reducing solar heat gain than the non-ventilated PV-DSF and also has a slightly better power output performance, whereas the non-ventilated PV-DSF has better thermal insulation performance. Based on this conclusion, the optimal operating modes for the PV-DSF have been determined and recommended for different weather conditions. A comprehensive numerical simulation model, based on EnergyPlus, has been developed to simulate the overall energy performance of the PV-DSF, especially the dynamic power generation performance under different weather conditions. To accurately predict the dynamic power output, this thesis also carried out a thorough experimental study and theoretical analysis on the impact of the solar spectral irradiance on the short circuit current of a-Si PV modules. Through introducing the air mass cumulative distribution function (AMCDF), a new empirical model for calculating the short circuit current of PV modules on sunny days was proposed. For predicting the short circuit current on overcast days, a new method, named weighted average spectral response method (WASR), was proposed by combining with an average photon energy (APE) database matrix, which is proposed to determine the APE under any sky conditions in local. The developed simulation model for the PV-DSF has been validated with measured experimental results to verify its accuracy. The comparison results showed that the error between the simulated monthly AC energy output and the measured one was less than 3%. With the developed simulation model, the annual overall energy performance of the PV-DSF was studied by using the weather data of typical meteorological year (TMY) in Hong Kong and Berkeley in California. In terms of power performance, the best orientation for PV-DSF installation in Hong Kong is 40 degrees south by west, in which the PV-DSF could generate the maximum energy of 39.4 kWh/m²/yr., while in Berkeley, the optimum orientation is 30 degrees south by west and the maximum energy output is 67 kWh/m²/yr. However, if taking the overall energy performance into account, the optimum orientation for PV-DSF installation in Hong Kong and Berkeley were 20 degrees south by east and due south, respectively. Based on the developed simulation model, sensitivity analysis has also conducted to investigate the impact of the air gap depth on the overall energy performance of PV-DSFs. Based on the analysis results, the optimum air gap range in Hong Kong and Berkeley were recommended to be 300-500 mm and 400-600 mm, respectively. From the above, the academic contributions of this thesis can be summarized into four aspects. Firstly, a novel ventilated PV-DSF prototype was developed in this thesis and its pretty good overall energy performance were comprehensively demonstrated by outdoor experiment. Secondly, a methodology and a comprehensive model were developed to simulate the overall energy performance of the PV-DSF, including the power generation performance, daylighting and thermal performances. With this model, the impact of some key parameters (such as the orientation, the air gap depth and the ventilation mode) on the overall energy performance can be determined. Thus, this model provides a useful solution for optimizing the design of PV-DSFs in different climate zones in the future. Thirdly, the impact of the diffuse solar radiation ratio (Rd) on the short circuit current was found in this research and the relationship between Rd and short circuit current of a-Si PV module was determined. Lastly, based on the research output of the solar spectrum study, two different models, viz. AMCDF model and WASR model, were proposed to predict the short circuit current of PV modules under any weather conditions. With these two models, the engineers can predict the short circuit current of any PV module more easily and accurately.
Subjects: Building-integrated photovoltaic systems
Buildings -- Energy conservation.
Facades -- Environmental aspects
Hong Kong Polytechnic University -- Dissertations
Pages: xxxviii, 279 leaves : color illustrations ; 30 cm
Appears in Collections:Thesis

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