Two recent studies, however, raised some eyebrows by indicating that the plants on a green roof may actually improve the performance of the photovoltaic solar cells themselves.
By absorbing rainwater and on rooftops and enhancing water evaporation, the plants in a green, or “living,” roof can reduce the ambient air temperature and mitigate the heat island effect on rooftops. In addition to providing natural insulation for buildings, the plants also create a better environment for solar cells, which perform best at lower temperatures.
According to preliminary research being conducted by the Bronx Design and Construction Academy, the efficiency rates for a solar array on a green roof are 3 percent higher than a solar array on a conventional rooftop.
The students and a professor at the Bronx Academy who conducted the Green Roof Integrated Photovoltaic Canopy experiment submitted a $100,000 grant through the Zayed Future Energy Prize last summer and are currently one of the top two finalists in the Americas region. The students have been invited to Abu Dhabi to present their findings at the annual World Future Energy Summit. The winners of the Zayed Future Energy Prize will be announced on Jan. 15, 2013.
Meanwhile, a separate study conducted by the American Solar Energy Society (ASES) suggests an even more synergistic relationship between green roofs and solar panels. Living roofs, the ASES researchers found, can also improve solar cell performance by filtering out pollutants and dust from the surrounding air that can interfere in the photovoltaic process. Operating a green roof in conjunction with a solar array, the study found, can boost solar panel performance by as much as 16 percent.
The wide variation in the results of the two studies has to do with differences in the types of solar cells being used, the plants that are included in the green roof ecosystem and the materials in the rooftops. However, both studies provide encouraging data that suggest a synergistic connection between living roofs and solar panels.