Green roofs can boost solar panel efficiency, study finds – pv magazine USA
It is believed that the improvements are the result of lower temperatures on the green roof.
The roofs of two adjacent office buildings in Australia’s Barangaroo district of Sydney have given researchers a rare glimpse into the real-life effects of green roofs on solar panels. The findings are significant: compared to the conventional roof, the solar panel placed above the plant beds had an average daily output of 39 kW, or 13.1% more.
The study was led by Peter Irga of the University of Technology Sydney and funded by the City of Sydney Council, with research on the International House conventional series and The green roof array of Daramu House, known as a bi-solar roof.
Both roofs generated significant amounts of solar energy in the eight months they were studied, with the conventional roof producing 59.5 MWh, while the green roof producing 69 MWh.
“Despite the similarities in construction and location, the effect of urban geometry on the solar radiation on any roof is made apparent outside the hours when the sun is near/at its solar peak… During these hours, the green roof produced an average energy efficiency of ~6 % higher than the conventional roof. Before and after these hours, the influence of urban geometry obscures reportable efficiencies (-3.6 to 16%),” the study said.
After adjusting for these differences, the panels on the green roof were found to be on average 3.63% more efficient on any given day. Subsequently, the green roof produced another 9.5 MWh of green electricity during the eight-month research period.
This efficiency improvement is thought to be a result of the green roof remaining much cooler during the day than the traditional concrete roof, meaning the panels did not overheat and therefore underperformed. In some cases the green roof was even 20°C cooler, while the temperature fluctuated much less in the evening.
Although it is gaining popularity, there is currently a lack of research confirming the benefits of green roofs. In addition, “there is very little research comparing similar buildings exposed to similar environmental conditions because of proximity,” the study noted.
In addition to the significant increase in solar panel output, the green roof was also found to have a nine-fold increase in insect species diversity, as well as a four-fold increase in bird species diversity. It also saw reductions in some air pollutants, improved stormwater management and improved building insulation.
“Given the magnitude of the positive impacts generated relative to costs, green infrastructure is perhaps the easiest and most efficient initiative we can take to make our cities sustainable,” the study said.
The study authors described their findings as “substantial,” though noting that only two roofs were checked.
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