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Photovoltaic Energy Performance in Relation to Roofing Types: An Investigation of the Thermal Interaction Between Building Roof Surface and PV Panels
Alshayeb, Mohammed Jawad
Alshayeb, Mohammed Jawad
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Abstract
Roofs comprise 20-25% of total urban surface area, and with different roofing technologies and photovoltaics, present an opportunity for buildings to move closer to net-zero energy. The conversion efficiency of photovoltaic (PV) panels in real world settings is lower than those measured in a laboratory under the Standard Testing Condition (STC) due to several factors such as differences in irradiance level, dirt and dust, shading, air speed, and air temperature. The operation temperature of PV modules has an impact on the conversion efficiency and output energy of the system. Since the efficiency of PV panels is reported based on the STC temperature of 25°C, PV manufacturers publish temperature coefficients relating losses in efficiency for each degree the temperature fluctuates from 25°C. Because there is thermal interaction between the PV panels and surrounding surfaces, the selection of roofing materials is important to roof-mounted PV arrays. For instance, green roofs and white roofs have surface temperatures below 50°C, while common roofing materials reach temperatures of over 75°C. This research investigated the thermal interactions between the building roof surface and PV panels by examining the PV panel temperature differences and energy output performance for those installed over a green roof (PV-Green), a white roof (PV-White), and a conventional black roof (PV-Black). Thermocouples were placed on the underside of the PV panels and between the roof surface and PV panels. The energy output from every PV panel was monitored. During the hours of the year with high temperatures, over 25°C, PV panels over the green roof consistently recorded lower underside surface temperatures and lower ambient temperatures than PV panels installed over the white or black roof. Due to the differences in PV underside surface temperatures, PV-Green generated more electricity than PV-White and PV-Black. There were slight differences in energy production between PV-White and PV-Black. In general, PV panels installed over a green roof outperformed PV panels installed over a white roof membrane and PV panels installed over a conventional black roof membrane.
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Date
2018-01-01
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University of Kansas
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This item contains archived web content.
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Alshayeb_ku_0099D_15785_DATA_1.pdf
Adobe PDF, 6.3 MB
- Embargoed until 2158-05-31
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Keywords
Architecture, Architectural engineering, Conventional black roof, Green Roof, Photovoltaic energy performance, Renewable Energy, Thermal interaction, White roof