Hydrological and Life Cycle Assessment of Green Roof Photovoltaic Systems

Traditionally, green roof (GR) and photovoltaic (PV) systems have been viewed as direct competitors vying for the same roof space. However, with appropriate design, synergistic effects can arise when these technologies are combined. This study is focused on two major areas: first, the cradle-to-use life cycle analysis of integrated systems in terms of energy and carbon emissions; and second, the hydrologic related effects of an integrated system including runoff, water retention, evapotranspiration, and soil moisture, among others. A probabilistic analysis was performed to examine the potential energy and carbon emissions of GR, PV, and integrated systems (GR-PV). The analysis demonstrates that a GR-PV system is a low-risk investment generating lower energy and carbon-emission pay-back time in comparison with separate GR and PV systems. The hydrology and vegetation growth of two full scale integrated systems was monitored at GRITlab between August 2016 and July 2017 with 1.2 m and 0.6 m differential height between GR modules and PV panels. Doubling the differential height (from 0.6 to 1.2m) did not significantly change the rainwater retention and peak flow reduction in the integrated systems. Larger vertical distance between PV and GR provided plants with more solar radiation and greater rain exposure, which led to more vegetation growth. GR evapotranspiration (ET) processes and modeling approaches for shaded and unshaded conditions were investigated using data from two GR modules installed at the Green Roof Innovation Testing laboratory (GRITlab) on the fifth-story roof of a University of Toronto building located on the downtown St. George campus. A modified Penman-Monteith equation was developed to provide improved prediction of hourly ET, specifically for GR applications. The modified equation improved ET estimates by 8-9% and 37% under non-water limited and water limited conditions, respectively for the GRITlab data. The net radiation and wind speed beneath PV panels was modeled as a function of length, height, slope and row-spacing of PV panels and diurnal wind/sun characteristics. ET rates beneath PV panels were shown to be most sensitive to PV panel row-spacing and length.Ph.D.2020-04-30 00:00:0