Influence of PV-Reflector Shading on Rooftop Heat Transfer, Building Energy Loads, and PV Power Output Incorporating Temperature Dependent Photovoltaic Efficiency

Date of Award

2022

Degree Name

Ph.D. in Mechanical Engineering and Aerospace Engineering

Department

Department of Mechanical and Aerospace Engineering

Advisor/Chair

Rydge Mulford

Abstract

Photovoltaic (PV) power output depends on the solar radiation incident on the PV, the module temperature, and the PV material properties. Augmenting reflectors is a common technique to reflect solar irradiation onto PV surfaces to increase PV power output supplied to the building. However, PV cell temperature is a function of solar energy incident on the PV surface; meaning increased solar sunlight on PV leads to increased PV temperature. The PV power output when considering the influence of PV temperature on efficiency is less than the PV power output without considering PV temperature. Additionally, PV installations on rooftops add shading to the building and reduce energy consumption during summertime, blocking solar energy from entering the rooftop for all seasons. As such, the energy consumption will be increased in the winter season as PV provides shade during the heating season. Providing more shading on rooftops by adding reflectors next to roof-mounted PV increases energy savings during the cooling season and further increases energy consumption in the heating season. PV power output depends on the slope of PV, the angle between PV and reflector, and the weather condition of PV, while energy savings and energy addition depend on roof location and absorptivity as well as eather conditions. Using TMY3 hourly data, this study investigates the influence of PV temperature on reflector-augmented PV power output in several United States cities. The study obtains PV efficiency with and without considering PV temperature and compares PV power output based on four different angles between PV and reflectors and PV and the horizontal line. The results show that temperature-dependent efficiency is less than temperature-independent efficiency, while power fraction during summer is higher than in the wintertime. In addition, the study investigates heat flux performance through PV-shaded roofs in three locations in the United States. The study obtains the energy savings and energy addition by adding PV shading on rooftops and presents the metric of PV effectiveness as a utility factor ratio calculated by adding energy savings to PV power output divided by energy addition. The utility factor shows that PV-shading is more effective in hot sunny weather than in cold cloudy weather. Finally, the study examines energy consumption, energy savings, and utility factor by adding reflectors to the roof-mounted PV array in the three locations. Different lengths of reflector augmented into PV model are investigated. The overall results indicate that providing more shading on rooftops decreases energy savings in the heat season and increases energy in the cold season. Adding reflectors further augments PV power, increasing the utility factor of the roof mounted PV array.

Keywords

Mechanical Engineering

Rights Statement

Copyright © 2022, author.

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