A Rooftop Agrivoltaic System: Pollinator Plant Establishment

Abstract

In a time of rapid habitat removal in favor of urbanization, green roofs have been recognized as a means to increase biodiversity while emulating native habitats in urban ecosystems. There is often competition over roof space for use as solar energy generation, or green roof space. Here we explore the inclusion of both green roof and photovoltaic (PV) energy generation systems stacked vertically in a rooftop system to better understand the impacts of PV arrays on six species of pollinator plants native to Colorado’s Front Range and Great Plains Regions. We conducted randomized and replicated plant establishment and growth studies in a simulated rooftop system in full sun and under a fixed mounted PV array over the course of the initial growing season. Additionally, we measured the plant growing environment, including air temperature, substrate temperature, and substrate moisture to quantify the differences in the conditions in full sun compared to conditions under the PV arrays. Light conditions were modeled. We find plant establishment and overwinter survivability is greater under the PV array, while the seasonal plant growth index varies depending on the plant species. Substrate moisture was significantly higher under the PV while substrate temperature trended towards lower daytime temperatures and slightly raised nighttime temperatures under the PV. Based on this study, the microclimate under the PV array is amenable to plant growth, and differences in plant response to the shade may closely resemble ecotones found in nature. The combination of rooftop agrivoltaics and traditional full sun green roof plantings may lead to greater native plant establishment, and therefore greater diversity of habitat niches in the built environment.