Solar power and green roofs are often thought of as separate solutions, however, the practice of combing the two technologies is growing in popularity in countries such as Switzerland, Germany, and Austria. Roofs that couple green roofs and solar power together are often referred to as biosolar roofs.

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What is a green roof?

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A green roof is a vegetated landscape built up from a series of layers that are installed on a roof surface (either layer by layer or as pre-prepared layers in trays.)

Green roofs last longer than conventional roofs, reduce energy costs with natural insulation, create peaceful environments and absorb stormwater.

On a wider scale, green roofs help to improve air quality and reduce the Urban Heat Island Effect, a condition in which city and suburban developments absorb and trap heat.

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What is solar power?

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Solar power uses the sun’s energy, either directly as thermal energy or through the use of photovoltaic cells and transparent glass to generate electricity.

Solar power is a truly renewable source of energy that does not produce any greenhouse gases or pollute water sources.

Installing solar panels on roofs helps to reduce one’s carbon footprint and electricity costs, it can even generate a profit by selling the unused electricity back to the grid.

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How the technologies work together

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Integrating green roofs and solar photovoltaic (PV) systems can enhance the way they work and their overall effectiveness by cooling and shading effects.

The results from numerous experiments display a positive outcome from their integration; green roof surface and soil temperature are reduced from shading and higher output of PV panels is achieved from the cooling effect.

If the micro-climate around panels is too hot the panels may not work efficiently. Green roofs help to keep ambient temperatures around the panels close to 25c, the ideal temperature for solar energy production.

The diversity of vegetation and fauna using the green roof should increase with the PV panels providing shaded areas underneath and rain run-off creating damper areas to the front and drier areas to the back.

This creates a ‘habitat mosaic’ which allows a wider variety of vegetation to flourish and, in turn, attract a wider range of butterflies, bees, beetles and other species.

The design of biosolar roofs, however, is critical. If too much emphasis is put on the solar panels and the green roof is used as purely decorative, the positives can quickly turn into negatives. For example, if the panels are placed too close together and entirely the wrong sort of plants take over.

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Creating more efficient cities

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Many experts believe that biosolar technology could deliver widespread environmental, social and economic benefits.

Vegetation lowers the heat load on a building’s roof and reduces air-conditioning needs and costs; cutting down on residents’ electricity bills and reducing their carbon footprint.

In addition, green roofs provide niche habitats which encourage biodiversity, can be used for food production, reduce urban heat, enables water recycling, improves air quality, extends roof life, and provides social amenity.

These benefits, coupled with the ability to become energy self-sufficient through the use of PV systems, create highly efficient and sustainable homes for city dwellers.

With the fight for space becoming an ever-worsening issue in cities, roofs provide an oasis of unused space that can be exploited to meet the energy needs of residents and support a vital habitat for wildlife.