Operational power performance of south-facing vertical BIPV window system applied in office building.

Significance Statement

Renewable energy technologies are increasingly finding their way as construction entities especially in non-residential buildings. This is because they reduce the high electricity consumption rates in these buildings and also contribute immensely in thermal and electrical load matching. Building integrated photovoltaics are one such technology that is being applied to structural components such as windows, walls, and roofs, which sets it apart from the stand alone Photovoltaic Power plants that only produce electricity. This paper focuses on the power efficiency of the Building integrated photovoltaic (BIPV) technology, especially those on vertical walls under actual operation as well as the factors that limit the performance of these technologies which include, the angle of installation, and shading.

Hyo Mun Lee and colleagues at Hanbat National University in Republic of Korea set out to investigate the operational power performance of south-facing vertical Building integrated photovoltaic window system applied in an office building. Their research work is published in Solar Energy.

In their study BIPV system with four arrays and inverters, was applied as a vertical curtain wall on the south and east face of a five-story office building, with attention paid to the south face only. Each floor face was divided into four sections, with the vision area having a typical blue-color double glazing, while the other three sections were made up of transparent BIPV window systems.

The study focused on elements that were likely to give a shading effect. These were an adjacent building of nearly similar height on the south face, a low hillock on the east face, and forty millimeter extruded louvers above each BIPV module. The study utilized measured data of irradiation, power generation and conversion efficiency of a power conditioning system.

Observations showed that the adjacent building provided no shading effect of direct solar radiation during the whole year, but the shading effect of diffuse solar radiation by adjacent building differs from the location of the BIPV arrays. The lower array experienced a greater loss as compared to the upper array. It was found that despite their short length, extruded louvers block the annual average insolation especially when the solar altitude is high during summer, and this had a greater effect on the first and fourth array. This resulted in system loss and capture loss of the BIPV.

The authors evaluated the shading effect by the hillock through the geometric shading analysis using sun-path diagram. This showed a solar access decrease between October and March especially in the early morning hours. The performance ratio analysis of the first and second array showed a significant operational degradation due to this shading effect.

They also observed a change in incidence angle at different times of the year due to changing solar altitude, resulted in irradiation loss with the highest being in the month of May due to the high incidence angle modifier.

From the research conducted it was evident that the external environmental conditions such as shading by adjacent buildings, short louvers, and vegetation have a significant effect on the power performance decline of the building integrated photovoltaic system and should therefore be considered during the design stage of this systems.

Reference

Hyo Mun Lee, Jong Ho Yoon, Seung Chul Kim, U. Cheul Shin. Operational power performance of south-facing vertical BIPV window system applied in office building. Solar Energy 145 (2017) 66-77.

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