Experiments were conducted in summer using two identical photovoltaic (PV) panels at two heights using three roofing types: white, black, and green (vegetated). For experiments at an 18 cm height, the mean power output of the PV-green roof system was 1.2% and 0.8% higher than the PV-black and PV-white roofs, respectively. At a 24 cm height, the benefit of the green roof was slightly diminished with power output for the PV above a green roof being 1.0% and 0.7% higher than the black and white roof experiments, respectively. These results were consistent with measured variations in mean panel surface temperatures; the green roof systems were generally cooler by 1.5–3 °C. A unique aspect of this research is the investigation into the effect of vegetation on the convective cooling of the PV panels. Panel heat transfer coefficients for the PV-green roof were 10–20% higher than for the white and black roof configurations, suggesting a mixing benefit associated with the roughness of the plant canopy. While the best PV performance was obtained by locating PV above a green roof, the relative benefits diminish with distance between the PV and the roof.
Measuring the Effect of Vegetated Roofs on the Performance of Photovoltaic Panels in a Combined System
Portland State University,
Portland, OR 97207
Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received November 13, 2015; final manuscript received August 19, 2016; published online October 3, 2016. Assoc. Editor: Carlos F. M. Coimbra.
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Ogaili, H., and Sailor, D. J. (October 3, 2016). "Measuring the Effect of Vegetated Roofs on the Performance of Photovoltaic Panels in a Combined System." ASME. J. Sol. Energy Eng. December 2016; 138(6): 061009. https://doi.org/10.1115/1.4034743
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