A biosolar roof is a roof on which plants and solar panels are installed . Does the presence of one inhibit the other or do they strengthen each other? The answer is the latter, explain Peter Irga, Fraser Torpey, Eamon Wooster, Charles Sturt, Robert Fleck of the University of Technology Sydney and Jack Rojan of the University of Canberra, who summarize their research. Vegetation cools the panels to near optimal operating temperature , increasing the maximum power of the solar panels from 21 to 107% depending on the month . At the same time , the shade created by the panels contributes to the development of several species : not only plants, but also insects, microorganisms and much more. The biosolar roof even attracts many birds. Therefore, rooftop biosolar can make an important contribution to net-zero cities by increasing biodiversity and rooftop solar energy production, the authors conclude. Growing urban populations and limited space have led to the introduction of green roofs and green walls covered with living plants. In addition to increasing biodiversity, green roofs can play another invaluable role by increasing the power of solar panels .
If the temperature of the solar panel exceeds 25℃, its efficiency is significantly reduced . Green roof at moderate temperature . So, we wanted to know: Can green roofs reduce solar heat production?
Our study compared “bi-solar” green roofs – which integrate a solar system with a green roof – and comparable conventional roofs with equivalent solar systems. We measure the impact on biodiversity and solar energy production, as well as how the trees support the installation of the panels.
As expected, green roofs support greater biodiversity. When the average maximum temperature drops by about 8℃, solar energy production increases by up to 107% during peak periods . And when some types of plants outcompete others , the plants will grow.
These results show that we don't have to choose between green roofs and solar roofs: we can combine the two and get double benefits.
[Various solar panels installed on the green roof of Daramu House in Sydney city centre.]
How was this research conducted?
Many studies examining single roofs are divided into “green roof” and “non-green roof” categories to measure differences caused by vegetation. A problem in such studies is "local confounding": the impacts of two nearby locations mutually influence each other. For example, a cool, green roof area can moderate the temperature in adjacent non-green areas.
In studies using single buildings, the buildings may be far apart or built too differently to compare.
The two buildings in our study are the same height, size and shape and are located next to each other in Sydney . The only difference is that Daramu House has a green roof and International House does not.
We 've selected a mix of native and non-native grasses and non-woody plants to attract many species that bloom throughout the season .
We used motion detection cameras to identify species on the roof and collected samples to look for traces of DNA. We documented changes in green roof vegetation to reveal the shading effects of solar panels on plants.
How do these signs affect plants?
In the open area, we observed little change in vegetation cover during the study period compared to the original vegetation community.
Plant growth is fastest and healthiest in areas around solar panels . Some species have a double layer. For this part, we chose fast growing plants to get a fully green roof as quickly as possible.
Vegetation experiences the greatest changes in the areas directly under and around the solar panels. The small sunflower , Aptinia cordifolia, becomes the dominant plant. Although the landing is relatively small, it takes up most of the space under and around the solar panels.
This was surprising: we didn't expect that the plants would prefer the shade under the panels to the open areas . This shows that a roof that is strong, healthy and shaded by solar panels will not hinder the growth of the garden .
We used environmental DNA (eDNA) studies to compare the biodiversity of green roofs and conventional roofs. Water samples were collected from both roofs and processed on site using citizen scientists' portable eDNA sampling devices to detect trace amounts of DNA released by species on the roofs.
In general, green roofs are home to four times as many species of birds , seven times as many species of arthropods such as insects, spiders and centipedes, and twice as many species of snails and snails as traditional roofs. Microorganisms such as algae and fungi are much more diverse.
Fortunately , green roofs have attracted unexpected views of the city . These include the blue-banded bee ( Amegilla cingulata ) and the metal shield bee ( Scutiphora pedicellata ).
The green roof reduces the surface temperature of the solar module to 9.63℃, and the roof surface to 6.93℃ . Reducing the average maximum temperature on green roofs by 8°C results in significant savings in heating and cooling energy in the building.
This temperature reduction increases the maximum power of the solar module from 21 to 107% depending on the month . Performance simulations show that extensive green roofs in Sydney's city center can generate an average of 4.5% more electricity, regardless of lighting levels .
Next steps: Rooftop biosolar can help cities reach net zero.
The next step was to design a roof and special greenery to increase biodiversity. Green roofs and other green infrastructure can alter urban wildlife activity and ultimately attract non-urban species.
Our green roofs also reduce stormwater runoff , remove various pollutants , and insulate buildings from extreme temperatures . Relatively inexpensive systems offer all these services with moderate maintenance and, most importantly, without energy costs.
Biosolar green roofs can clearly make an important contribution to cities without revenue. And the necessary space, which currently has no other application.
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Peter Irga is an ARC DECRA Fellow and Senior Lecturer in Air Pollution and Noise at the School of Civil and Environmental Engineering , University of Technology Sydney. Eamon Worcester is a PhD student
at Charles Sturt University's Galbally Institute,
Fraser Torpy Director, Plant and Environmental Quality Research Group , University of Technology Sydney.
Jack Rosahan - PhD, Institute of Applied Ecology , University of Canberra ,
Robert Fleck - Research Scientist, Faculty of Life Sciences, University of Technology Sydney.
This article is republished from The Conversation under a Creative Commons license. Read the original article
