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Green solar roofs: Synergy in action

A green roof significantly increases the performance of photovoltaic panels

The benefits of green roofs in terms of energy savings, CO2 emission reduction, and biodiversity enhancement are widely recognized. In recent years, numerous studies have shown that green roofs positively influence the performance of solar panels.

Innova Top Green’s Solar Green Roof offers an effective combination of rooftop greening and photovoltaic system that significantly increases building energy efficiency, contributes to improving the air quality and ecological environment of our city, and – globally – to increasing the resilience of planet Earth to climate change.

One of the most recent studies was conducted in the Sydney area in 2021 for eight months. It compared the performance of a conventional photovoltaic (PV) solar system with that of a combined solar system on a green roof (bio-solar roof). Two identical office buildings, located next to each other in Sydney’s Barangaroo district, provided solar researchers with the perfect opportunity to test a long-held assumption. Would a green rooftop make solar panels more efficient? It turns out the answer is YES.

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Researchers compared the electricity production from solar panels on two neighboring roofs. Photo: Ursula Malone, ABC News Australia

The researchers found that the green roof improved efficiency by up to 20% at peak times and by 3.6% – equivalent to 9.5 MWh of additional energy production – over the entire period of the experiment.

The green roof removed an additional 8.8 tonnes of greenhouse gas equivalent to carbon dioxide compared to standard rooftop solar panels, equivalent to planting 110 trees. Over the course of 8 months, the green roof generated an additional $2,595 worth of renewable energy.

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Surface temperatures on the green roof were significantly reduced – in some cases by up to 20°C in summer, suggesting a potential reduction in the urban heat island effect. Another advantage of the integrated roof system of the bio-solar roof (solar panels and green roof) is the insulation, which prevents heat transfer inside the building as well as heat retention during cooler periods.

On hot days, surface temperatures were up to 20 degrees lower on the green roof compared with the standard solar roof. (Supplied: University of Technology, Sydney.)

In addition, stormwater monitoring of both roof systems shows that the bio-solar roof can reduce storm sewer flows by more than 600 liters per second compared to a conventional solar roof. This can reduce the effects of flooding during prolonged and heavy rainfall.

Overall, an integrated green roof PV system outperforms a conventional PV system, confirming that rooftop greening-green infrastructure is among the easiest and most effective solutions that, through its multiple benefits, can help increase the resilience of our cities to climate change.

One of the main conclusions of the study: green roofs can help combat climate change.

The study of the effect of a combined green roof with solar panels was led by Dr. Peter Irga from the University of Technology Sydney and funded by the City of Sydney Council.

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Photo: Ursula Malone, ABC News Australia

More information about the study can be found here.

Based on this, as well as numerous other studies related to increasing energy efficiency through rooftop landscaping, the question of what to choose comes up

GREEN ROOF OR SOLAR ROOF?

The right choice is a combination of a green roof and solar panels.

It is a misconception that you have to choose between a green roof and a solar system. On the contrary, when combining the two, significantly increased energy efficiency and synergy are achieved, whether for electricity generation (photovoltaic) or heating and hot water applications (solar thermal).

A flat roof is one of the most suitable locations for a solar PV system, as the solar panels can be adjusted to the correct angle to achieve the most suitable orientation.

Increased efficiency of photovoltaic modules on a green roof: the efficiency of the solar panels depends on the temperature of the modules and the ambient air temperature. The basic rule is: “the warmer the solar panel, the lower its performance“. In reality, the modules heat up significantly as a result of solar radiation. This is exacerbated by the hot surface of a flat or pitched roof, such as a bare waterproofing membrane or a shingle roof. However, if combined with a green roof, solar panels will work significantly better.

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Solar green roof at Munich Technology Center (MTZ), Photo: ZinCo

The green roof maintains a lower surface temperature through its cooling effect caused by the evaporation of plants. This lowers the ambient air temperature and the photovoltaic panels achieve and maintain higher output, improving their overall efficiency.

The most common way around the world to create a roof garden and rooftop landscaping is an extensive green roof with cold and drought tolerant sedums. Rooftop greening and performance enhancement of solar panels is quick and affordable by laying pre-vegetated sedum mats.   

Innova Top Green’s pre-cultivated Sedum mats are pre-grown and acclimatized in the high fields of the Balkan Mountains. The Sedum mats require little maintenance and are a reasonable (water-)free alternative to grass in many applications. SeduMixmat ITG-01 is an all-purpose green blanket.

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