Building Energy Savings and Power Output Augmentation of Roof Mounted Photovoltaic Using Co-Located Rooftop Reflectors

Abstract

Photovoltaic (PV) panels installed on building rooftops yield a positive influence on the thermal performance of the building due to the shading of the PV panels, decreasing cooling loads while causing a smaller increase in heating loads. Additionally, the electrical power output of PV panels has been shown to be increased by including reflectors between PV rows, concentrating the solar flux onto the active portion of the panels. When implemented into the spaces between the rows of a roof-mounted PV array, reflectors might further improve the positive thermal effects of rooftop installed PV arrays. This work focuses on predicting rooftop heat flux and temperature for a building rooftop equipped with PV panels and reflectors. The saved energy load, additional energy load, PV power output, rooftop heat flux, and the utility factor (ratio of positive building energy impacts to negative building energy impacts) are reported parametrically for variations in the rooftop absorptivity and reflector area for three US locations. Utility factors of 375, 140, and 160 are found for Phoenix, AZ, Boise, ID, and Dayton, OH, respectively, for a reflector covering the full area between panels with a roof having a minimal absorptivity. A building in Phoenix, AZ exhibits a 15% increase in the utility factor of the PV-building system when reflectors are incorporated compared to a PV-building system without reflectors, while a building in Dayton, OH showed a 22% increase in utility factor when reflectors are included between the rows of a roof-mounted PV array.