An Analysis of Real-Time Measured Solar Radiation and Daylight and Its Energy Implications for Semi-Transparent Building-Integrated Photovoltaic Façades

For analyzing cooling loads, day-lighting, and building-integrated photovoltaic (BIPV) systems, solar radiation and daylight illuminance data are required. However, these data are sparse. Furthermore, studies have shown that the energy potential of building-integrated photovoltaic (BIPV) systems for the entire building skin (BS) and unconventional orientations, such as east, west, and north need further exploration. Thus, this study presents findings from measured solar data and an energy analysis of semi-transparent BIPV. Firstly, solar radiation and daylight data measured from June 2019 to May 2020 in Hong Kong are presented. The analyzed solar-radiation data were used to determine the solar-energy potential of BIPV for BS and the four principal building orientations (i.e., N, E, S and W). With a simple analytical approach, the solar data’s building-energy implications for semi-transparent BIPV were assessed. The findings showed that the annual average horizontal global-, diffuse-, and direct-irradiance values were 291.8, 164.3, and 127.5 W/m²/day, respectively. Similarly, 120, 72, and 107 klux were obtained as the peak global, diffuse, and direct illuminance, respectively. Furthermore, the results show the potential of using BIPV on the entire BS in Hong Kong. It was also observed that a semi-transparent BIPV façade integrated with daylight-linked lighting controls could offer significant energy savings in electric lighting and cooling while also producing energy. In particular, BIPV façades with a large window-to-wall ratio (WWR) of 80% can provide an overall energy benefit of up to 7126 kWh.

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