Biosolar Green Roofs
In a world facing significant challenges such as population growth, urbanization, high energy consumption and loss of biodiversity, it is essential to find sustainable solutions in the urban environment. It is estimated that the global population will reach 10 billion inhabitants by 2050, more than 80% of the European population will live in cities, and energy consumption, in the residential sector alone, will increase by 48% between 2012 and 2040.

We need to generate electricity locally, using smart technologies, to make cities bigger autonomous and less vulnerable to energy crises. Photovoltaic panels have gained popularity in building design due to their ease of implementation and their independence from microclimatic variations. However, their efficiency remains lower compared to other renewable energy generation systems (even with the best technologies it is still below 30%). On the other hand, if we put only photovoltaic panels on all roofs, we can reach the so-called “heat island effects”, which appear around dark and rigid surfaces.

Numerous researches are being carried out with the aim of increasing the efficiency of photovoltaic
systems by integrating them with green roofs. Thus a balance is created when the solar panels are combined with Sedum type vegetation, small shrubs or even vegetables on roofs, plants cool the air behind the panels through the process of evapotranspiration. 

Studies have shown that Biosolar roofs can cool the PV surface temperature, leading to a 5-15% increase in electricity production compared to conventional roofs. Depending on factors such as plant types, roof performance and climate conditions, PV green roofs can contribute up to 8.3% of a building’s total energy consumption. On the other hand, photovoltaic panels shade the vegetation, giving it better resistance to drought. The combination of green roofs and photovoltaic panels has demonstrated positive effects on albedo, system performance and self-consumption rates.

The advantages of the biosolar system compared to photovoltaic systems installed on conventional roofs
The advantages of the biosolar system compared to photovoltaic systems installed on conventional roofs
The benefits of combining PV installations with green roofs extend beyond energy production. Research conducted in Sydney, Australia, compared conventional solar PV systems with green roof PV systems over an eight-month period. Two identical office buildings next to each other in Sydney’s Barangaroo provided a perfect opportunity for solar researchers to test the performance of different systems. The study was led by Peter Irga from the University of Technology Sydney and funded by the City of Sydney Council, with research conducted on the conventional solar panel system at International House and the biosolar green roof system at Daramu House (1800 m2, 10,000 plants, 12 different species).

The results are significant:
Compared to the conventional roof, the solar array placed on top of the plant cover had an average daily electricity production of 39 kW, i.e. 13.1% higher.

The research found that the surface temperatures on the green roof were significantly lower, in some
cases up to 20°C during the summer. This improved solar energy production by 3.6% over the eight months of the project.

Despite the similarities in construction and location, the effect of solar radiation on each roof is evident outside of hours when the sun is near its solar peak. During these hours, the green roof produced ~6% higher average energy production than the conventional roof. Before and after these hours otable performance results are shown(-3.6 – 16 %),” the study states. After correcting these differences, it was found that green roof panels were, on average, 3.63 % more efficient on any given day. Additionally, over the course of the eight-month study, the green roof produced an additional 9.5 MWh of green electricity, with the conventional roof producing 59.5 MWh, while the green roof produced 69 MWh.

The overall results demonstrated increased energy production, better rainwater filtration, an efficient
building insulation and an unexpected increase in animal biodiversity. The green roof remained significantly cooler than the traditional roof, resulting in improved efficiency of the photovoltaic panels and reduced urban heat island effects. On the other hand, the green roof absorbed greenhouse gases (almost nine tons of greenhouse gases, the equivalent of planting 110 trees) and provided additional ecological and aesthetic benefits.

"The reduction in surface temperature shows how green roofs could play an important role in combating the Urban Heat Island Effect, a major problem in our cities."

To further optimize PV roofs, specially designed, bifacial PV modules can be fitted that can be installed vertically. This configuration reduces the wind load while providing increased energy production in the morning and evening. Despite the presence of shaded and underground areas with albedo factors less than 0.2, the bifacial installation with a rated output of 9.09 kWp achieved a specific yield of 942 kWh/kWp in one year (11.08.2017-10.08.2018). This is close to the typical values of 1000 kWh/kWp obtained for south-facing PV systems in the same region.

Photovoltaic systems with vertically mounted bifacial photovoltaic module
Photovoltaic systems with vertically mounted bifacial photovoltaic module

The rooftop agrivoltaic system is another innovative solution to meet the challenges of urbanization and food production. Given that land space available for traditional agriculture is limited, unused building roofs offer vast potential for growing food. Rooftop agrivoltaics takes this concept further by integrating solar panels into rooftop farming systems.

This mutually beneficial approach allows the plants to evaporatively cool the solar panels, while the solar panels partially shade the plants from UV radiation and extreme temperatures in the often water-limited growing environments of green roofs. 

The protection that solar panels provide slows the rate of water use by plants, which in turn reduces drought stress on food crops.

Lettuce growing under semi-transparent solar panel modules in a simulated rooftop agrivoltaic system at the Colorado State University Foothills Campus. Photo: Thomas Hickey
Lettuce growing under semi-transparent solar panel modules in a simulated rooftop agrivoltaic system at the Colorado State University Foothills Campus. Photo: Thomas Hickey

Solar panels can also protect crops from extreme weather conditions and generate electricity at the same time. Potential benefits of rooftop agrivoltaic installations include increasing the resilience of urban food systems, expanding renewable energy production, and reducing water consumption.

Combining green roofs, photovoltaic panels and rooftop farming offers innovative solutions to the challenges faced by densely urbanized areas. By integrating these technologies, cities contribute to the production of smart electricity, biodiversity conservation, improved stormwater management, temperature regulation and the improvement of urban spaces. With a holistic approach to design, rooftop landscapes can also have great experiential value. In addition to ecosystem services and energy production, green roofscapes can also provide beauty and cultural expressions with aesthetic and recreational qualities.

"Considering the size of the positive impact generated in relation to the costs, ecological infrastructure is likely the simplest and most effective initiative we can take to contribute to the sustainable development of our cities."

The E-Biosolar System

The E-Biosolar system is an integrated photovoltaic system, specially designed for green roofs, it is a professional solution to produce renewable photovoltaic energy on the green roof. The system can be installed on both new and renovated buildings, it allows the layout on the entire surface of the roof. Thanks to the installation, the roof is considered biodiverse, in the shaded areas, created by the placement of the panels, plant areas with a different microclimate than those located on the sunny side are formed. Elevated modules allow light to penetrate and provide a moisture layer to the vegetation.

The E-Sedum Vegetation Cover

The E-Sedum vegetation cover contains between 10-12 different species of Sedum. The plants have a relatively small height and are characterized by increased capacity for self-regeneration, they are resistant to drought, sun, wind and frost, and develop very well under green roof conditions.

The Sedum roll offers a wide variety of colors and shapes, contains plants with leaves of various sizes, represents an economical solution for creating a carpet of vegetation that provides a high degree of coverage immediately after installation.

Related Blogs