In urban areas, the glazed facades of high rise buildings offer substantial, untapped potential for solar energy generation. A research group called ArKol led by the Fraunhofer Institute for Solar Energy Systems (ISE) has developed two novel solar thermal facade concepts – a solar thermal blind and a strip collector – which can be integrated in an architecturally appealing way.
Facades offer several advantages over rooves for solar collection on tall buildings. In winter, when the sun is lower, the facade absorbs more sunlight when power and heating is needed most. In summer, the facades collect less sunlight and don’t generate excess heat, thereby reducing the load on the system and extending its service life. Furthermore, the roof surface of tower blocks is often occupied by structures like lift shafts.
The main obstacle to the widespread use of solar panels on facades so far has been “reservations of potential customers about the appearance of the collectors,” says Michael Hermann, from the ISE’s Thermal Systems and Building Technology business unit, speaking to the journal . This provided the impetus for the project.
The new solar thermal blind has moveable slats which absorb heat, that is then transferred into the collection channels. When installed in the interspace between the double-facades of glazed buildings, the solar thermal blinds provide a dual function: collecting the heat (temperatures in the gaps can reach 100°C) and channelling it away, while providing protection from the sun’s rays.
The Fraunhofer ISE team are also working on improved designs for strip collectors to be fixed to the outside of buildings. The new models offer architects far greater flexibility regarding shape and size, colour and spacing. This is technically possible because heat is transferred to the collection channel “dry” rather than via hydraulic means. These collectors can be easily retrofitted to existing buildings.
In order to drive adoption of the technology, Hermann says, “The planning effort should be reduced, and simplified assembly and installation should be made possible.”