Research hones in on the ultimate green roof

Last month, three researchers at Portland State marked the end of the first four years of research on the interaction between solar panels and planted green roof installations. 

The project was funded by the National Science Foundation and partners including the Institute for Sustainable Solutions, Oregon BEST, the city of Portland, and Portland General Electric. A separate National Science Foundation grant is backing a partnership with the Oregon Museum of Science and Industry, known as OMSI, to translate some of the work into interactive displays for curious young minds. 

Collaborators on the grant included Carl Wamser, a solar specialist and professor emeritus of Chemistry; David Sailor, director of the PSU Green Building Research Laboratory and professor of Mechanical and Materials Engineering; and Todd Rosenstiel, a green roof specialist and assistant professor of Biology. 

The trio set out to prove that green roofs, also called ecoroofs, and photovoltaic arrays, installed in the same space can be symbiotically helpful to each other, the plants in the green roof trays keeping the solar cells cooled for optimal performance, and the shade provided by solar panels keeping the plants healthy. 

“The differences are very subtle,” Wamser said. “Both systems do absolutely fine. And although whether they both do better is marginal, installing both is a good way to optimize roof space.” 

The study collected a wealth of information about the performance of systems—in fact researchers claim the test site that was installed on the south-facing roof of PSU’s Science Research and Teaching Center building is likely to be among the most heavily instrumented site of its type in the world. Some 315 data streams feed in from 263 different sensors, which are monitoring 21 different types of data from different locations. For example, soil moisture sensors in each pan collect information on the environment of plants living under the panels or exposed to the elements. 

The study also cleared the way for further research and partnerships on everything from plant choices to the effects of photovoltaic panels on local temperatures. 

Todd Rosenstiel and Carl Wamser.

For example, Rosenstiel is looking at the value of green roof installations not only for their ability to naturally retain and filter stormwater, but also for their CO2 sequestration. Green roofs can also add insulation benefits to buildings and provide habitats for wildlife. 

“It’s been pretty interesting ecology up there,” Wamser said of the test site. 

Working with OMSI, Wamser and his colleagues are developing displays that will find ways to present some of the findings to the public. Within the next year, a new display at OMSI will shine a light on how solar cells and green roofs work and interact with the world around them. 

The research has so far fueled five journal publications, a master’s thesis, and a passel of conference presentations. It also gave rise to an episode of a TV series called Green Science Oregon.  It is expected to remain a viable and useful research site for many more years.

Green Science Oregon Episode 1 Trailer from WVP on Vimeo.