Do solar panels fit on green roofs?

Green roofs help to compensate for urban sealing, especially in densely populated areas. The green roof insulates the building and provides it with air conditioning. Anyone who relies on solar energy in the course of energetic renovation can even install a solar panel on a green roof. We explain what you need to know about this.

What is a green roof?

A green roof, i.e. the planting of vegetation on a roof, is, like a green façade, a green building, which is one of the ecological building measures. A wide variety of plants are suitable for green roofs, which are planted on the roof in different greening systems. Ecology therefore also speaks of settlement biotopes.

What are the advantages and disadvantages of a green roof?

Green roofs provide a kind of protective layer that protects the roof beneath from direct contact with environmental influences such as sunlight and rainfall. The protection is therefore physical, including thermal and mechanical. Thanks to the green protective layer, the functionality of the roof cladding, in particular its sealing function, can be maintained in the long term.

Because the green layer absorbs, stores and can release rainwater again (evaporation), it noticeably cools the rooms under the green roof in summer. This makes air conditioning unnecessary.


At the same time, the green roof ensures that the rooms under the planted roof do not cool down as much in winter: It acts here as a thermal insulation layer.

A Green roof, depending on its design, corresponds to an up to 80 millimetres (mm) thick insulating material of the so-called thermal conductivity group (WLG) 040. Researchers say a combination within photovoltaics and green roof would be amazing and it is called ‘solar green roof’ or ‘bio solar roof’.

Green roofs retain rainwater: More than half of the annual rainfall evaporates. Green roofs thus considerably relieve the drainage systems in settlements and the connected sewage treatment plants. This also has financial advantages, because if the wastewater charge splits the costs for wastewater and precipitation water, there is a savings effect for the building owner.

Roof planting makes its contribution to the urban climate: it filters dust and pollutants from the air and has a cooling effect that counteracts the heating of sealed surfaces in the city.

Green roofs give nature space: animals and plants can settle there. In this way, the bio solar roof contributes to maintaining or increasing the diversity of species in urban areas.

The above-mentioned advantages are offset by the disadvantages of green roofs, namely the comparatively higher acquisition costs and the absolutely necessary maintenance effort.

How do solar panels and green roofs fit together?

If you are dealing with energy-related measures for your building, the combination of various individual measures can often achieve higher effectiveness on the one hand and thus also save more energy and the resulting costs on the other.

On the other hand, the positive effect on the local climate is also often increased.

While the green roof brings the above-mentioned advantages, a solar thermal system that uses solar energy to generate heat for domestic water and space heating provides independence from energy sources such as oil, gas, and wood.


Clearly, the solar thermal collectors “colonize” roof surfaces and thus enter into direct competition with the plant colonizers of the same, which are applied as part of a green roof. Whereby with an elevation on flat roofs and slightly inclined roofs it is advisable to optimize the angle of incidence.

Living space, i.e. space to grow and flourish, would thus be left for the plants under the collectors. But would enough light reach the plants? After all, the plants under the collectors would hardly be exposed to direct sunlight. However, if the collectors were placed at an angle of between 10 and 15 degrees, light from behind or from the sides would reach the plants.

Depending on the location and orientation of the green roof, the greenery could benefit from the sun’s position, which changes with the time of day and season. Of course, the plant communities used for greening would then have to be adapted to the semi-shady location under the collector surfaces.

And what about water, the elixir of life?

The rainwater retention effect of the green roof would not be significantly affected by the partial shade. In order to optimally distribute the rainwater that would drip from the lower edge of the collector onto the green roof, the substrate height (breeding ground for green roofs) could be slightly increased in these areas so that the rainwater would also flow under the collectors.

Or suitable drainage systems could be laid under the collectors. On the side of the elevations, nothing would stand in the way of this or that possibility.

Important: Not all solar thermal collectors are the same. The different performances of collectors result from their construction and the technology with which they work. While it is often possible to compensate for a lower collector output with a larger collector surface if the roof surface is large enough, this approach is not advisable for green roofs.


Here, the aim is to shade the green roof area as little as possible. A combination of green roof and high-performance collector is therefore certainly recommended. Attention should be paid to the sustainability of the collectors, which is also determined by the heat-conducting fluid itself, among other things, that they use.

Water-glycol mixtures, which have to be replaced in the solar circuit after a certain running time, are opposed here to pure water systems. The latter is certainly better suited to green roofs because of their greater sustainability.

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