In Sydney, UTS researchers tested a biosolar green roof that cut panel temperatures by up to 9.63°C and increased maximum solar output by up to 107%, depending on the month

If you've ever stood on a scorching roof in summer, you'll know how much heat concrete and other hard surfaces can absorb. That heat can also affect solar panels, whose efficiency declines as their temperature rises. A team from the University of Technology Sydney (UTS) set out to test whether vegetation could help address the problem. Their study compared a green roof fitted with solar panels, known as a biosolar roof, with a conventional rooftop solar system. The results showed that combining vegetation and solar panels could lower panel temperatures while improving solar performance.

Why rooftop heat is such a big deal

Solar panels need sunlight to generate electricity, but higher operating temperatures can reduce their efficiency. Plants can help moderate rooftop temperatures through shade and evapotranspiration, the release of water vapour from vegetation. Green roofs are already used for thermal and stormwater benefits in cities, so the researchers wanted to see whether the same cooling effect could also help solar panels.


The study compared two nearby buildings in Sydney's central business district. Daramu House had a biosolar roof combining vegetation and solar panels, while International House had a conventional rooftop solar system. The buildings were similar in size and construction, allowing the researchers to compare the two systems under similar conditions. UTS reported that the green roof reduced solar-panel surface temperatures by up to 9.63 degrees Celsius. The temperature reduction was associated with a 21% to 107% increase in the panels' maximum output, depending on the month. UTS also reported that performance modelling indicated an extensive green roof in central Sydney could produce an average of 4.5% more electricity at a given light level.

More than just cooler panels

The researchers also examined how vegetation responded to having solar panels installed above it. Vegetation growing beneath and around the panels appeared to perform particularly well, although the response varied among plant species. Several species increased their coverage, while the Baby Sun Rose (Aptenia cordifolia) became dominant beneath and around the panels despite having been planted at relatively low density. Its coverage in the shaded areas increased from about 6% initially to about 85% during the study.

The finding suggests that solar-panel shading does not necessarily prevent vegetation from establishing on a green roof. However, the response was not uniform across all species, making plant selection an important part of designing a biosolar roof.

The rooftop also supported a wider range of wildlife than the conventional roof. UTS researchers found four times as many bird species, more than seven times as many arthropod species, and twice as many snail and slug species on the green roof. eDNA surveys also found greater microorganism diversity, including algae and fungi. Blue-banded bees and metallic shield bugs were among the species recorded on the roof.

The green roof also provided environmental benefits beyond biodiversity. Separate research on the Sydney site found that the vegetation and growing medium helped manage stormwater runoff and retain some contaminants. The biosolar system also provided thermal insulation for the building.

What this means for city living

The UTS findings suggest that solar panels and green roofs do not necessarily have to compete for rooftop space. A biosolar roof can combine electricity generation with vegetation, while the plants can moderate temperatures and provide habitat for urban species. The study therefore offers a potential way to make more use of limited rooftop space in dense cities.

The research also points to the importance of choosing vegetation that can cope with the conditions created by solar panels. The Sydney roof showed that some species performed particularly well in shaded areas, while others responded differently. That means the design of a biosolar roof needs to account for both solar-panel performance and the requirements of the plants.

As cities expand and rooftop space becomes increasingly valuable, combining solar generation with green infrastructure could provide several benefits from the same surface. The Sydney study suggests that rooftop gardens and solar panels can be designed to work together rather than necessarily competing for space.