Photovoltaic Array Influences the Growth of Green Roof Plants

Abstract

A multi-faceted research project was conducted on a modular green roof in semi-arid, high elevation Denver, Colorado U.S.A. A photovoltaic (PV) array ran along the southeastern edge of the research area and visibly influenced the plant growth, cover and biomass. Plants grown near the PV prospered compared to plants in the exposed area. Average summer temperatures in the modules under the PV array were cooler with less temperature variation compared to the modules located in the exposed areas of the green roof. Shading structures integrated on green roofs may produce effects that resemble natural ecotones tending towards greater plant coverage and biomass, and therefore greater green roof resilience.

Solar Green Roofs: A Unified Outlook Twenty Years On

“…[17] The green roof areas beneath and close to the PV array remained fully vegetated, whereas coverage in the exposed areas was patchy which is, the scholars noted, a typical condition in moisture-deprived plants exposed to high levels of direct solar irradiance (bottom of Figure 2). [17] As mentioned above, the biodiversity potential habitat for wildlife in a solar green roof is enhanced in comparison to a green roof, and can be further enhanced using competences from horticulturalists and conservation scholars. [8] For instance, since 1999 the green roof the Hall 1 of Messehalle Basel (top of Figure 3, in Switzerland) with its 7 cm of volcanic substrate planted with low growing Sedum species, flowering herbs and forbs includes a large photovoltaic array deployed over 1,900 m 2 of green roof which produces 215,000 kWh/year.…”

“…[16] Testing a properly installed set of PV modules (and not single modules) over a green roof comprising eight plant species including Opuntia fragilis ( Figure 2), a team of scholars in Colorado found that the shade cast by the PV module string during the morning hours establishes gradients in substrate moisture, solar irradiance, and temperatures, with the substrate surface acting as a thermal sink relative to exposed roof surfaces. [17] Temperature variations below the PV modules, for example, were markedly lower amounting to 3.92°C and 6.36°C, respectively, for substrate surface beneath the modules in sheltered areas and in exposed areas. [17] The green roof areas beneath and close to the PV array remained fully vegetated, whereas coverage in the exposed areas was patchy which is, the scholars noted, a typical condition in moisture-deprived plants exposed to high levels of direct solar irradiance (bottom of Figure 2).…”

“…[17] Temperature variations below the PV modules, for example, were markedly lower amounting to 3.92°C and 6.36°C, respectively, for substrate surface beneath the modules in sheltered areas and in exposed areas. [17] The green roof areas beneath and close to the PV array remained fully vegetated, whereas coverage in the exposed areas was patchy which is, the scholars noted, a typical condition in moisture-deprived plants exposed to high levels of direct solar irradiance (bottom of Figure 2). [17] As mentioned above, the biodiversity potential habitat for wildlife in a solar green roof is enhanced in comparison to a green roof, and can be further enhanced using competences from horticulturalists and conservation scholars.…”

Green Roof Research in North America: A Recent History and Future Strategies

“…Green roofs cool ambient rooftop temperatures in summer and with cooler temperatures solar panels produce more energy (Alshayeb and Chang 2018;Gupta et al 2017;Hui and Chan 2011;Köhler et al 2007;Ogali and Sailor 2016;Sherba et al 2011). Solar panels on green roofs shade plants, therefore reducing evapotranspiration rates and mitigating water stress (Alshayeb and Chang 2018;Bousselot et al 2017;Köhler et al 2007;Ogali and Sailor 2016). Solar panels also moderate extreme temperatures on rooftops to the benefit of plants in both summer and winter (Bousselot et al 2017).…”

“…Solar panels on green roofs shade plants, therefore reducing evapotranspiration rates and mitigating water stress (Alshayeb and Chang 2018;Bousselot et al 2017;Köhler et al 2007;Ogali and Sailor 2016). Solar panels also moderate extreme temperatures on rooftops to the benefit of plants in both summer and winter (Bousselot et al 2017).…”