The goal of this research is to provide data that will advance the ability to design integrated green roof - photovoltaic array systems that can be optimized for multiple purposes on urban roofs. The fundamental research question to be addressed is: Can green roof design and/or management be altered to enhance both photovoltaic energy production and green roof function in a combined technology system. The research will use the Portland State University (PSU) Photovoltaic Test Facility, but the concepts and results generated should be broadly applicable to other urban systems, based on the project's modeling efforts. A suite of experimental green roof microcosms will be established to test hypotheses examining the relationship between green roof properties (species composition and evapotranspiration) on photovoltaic energy production and roof carbon gain. In addition, the impact of these technologies (separately and in combination) on building energy consumption and the development of the urban heat island effect will be investigated. Direct use and implementation of results will build upon collaborations with the City of Portland Bureau of Environmental Services, Portland General Electric, Oregon BEST (Built Environment and sustainable Technology Center), Gerding Edlen Development, and GreenWorks, with planned outreach components with the Oregon Museum of Science and Industry. The project will provide interdisciplinary research training for 8 to 10 undergraduate research assistants and three graduate students from PSU. Through development of a senior capstone course, engineering students will participate in key design aspects of the project. The research will support an emerging collaborative relationship among faculty members in multiple departments at PSU, an important aspect for research progress in environmental sustainability.
This NSF-sponsored project has established a research site consisting of multiple green roof pans with integrated photovoltaic panels. When people visualize a "green" function for a rooftop, it is typical to imagine either a green roof or solar panels. With this research, we are demonstrating that both can coexist and meet all of their functions at least as well as they would have done independently. The study has been investigating interactions between the functions of the green roofs (for example, thermal building insulation, rainwater retention, and carbon dioxide sequestration) and the functions of the photovoltaic panels (electrical power production). This installation of green roofs integrated with photovoltaic panels is likely to be among the most heavily instrumented research sites of this type in the world. We have 315 data streams from 263 different sensors monitoring 21 different types of data from different locations (for example, soil moisture sensors in each pan at different depths either under the panels or exposed to the elements). Results from this site have been used to improve models for the calculation of the effects of green roofs and photovoltaics on thermal properties of buildings and the urban heat island effect. This project has generated new knowledge about the evolution of biosystems in green roof plantings, the effects of shade, irrigation, and plant choices on the development and function of green roofs, and the effects of both green roofs and photovoltaic panels on local heat transfer. We have found that the water retention capabilities of green roofs depend significantly on the nature of the plants and soil organic matter; a mix of plants is generally more effective than a single type such as sedum. The output of the photovoltaic panels depends on their temperature, which depends on the thermal and reflective properties of the nearby roofing material; white roofing is comparable to green roofs, while darker roofing lowers photovoltaic efficiency. Knowledge from this project is expected to help disseminate useful information about green roofs and photovoltaics to facilitate their implementation. In the long run, we expect that the findings will help to inform architects and engineers in designing buildings that can take advantage of both green roofs and solar panels. Citizens can become more knowledgeable about both green roofs and photovoltaics via the information on our website (http://solar.pdx.edu) or activities we have been developing at the local science museum in Portland (OMSI - Oregon Museum of Science and Industry). This project is included in a separate NSF-sponsored project that is bringing this research and other research on Professor Wamser’s laboratory to the general public via activities developed for OMSI.
