Office buildings with plate glass windows may provide a nice view for workers, but they're certainly not ideal when it comes to energy-efficiency. Among other things, the sunlight that pours through them can raise the temperature in the office, causing the air conditioning to come on. Now, however, researchers from Germany's Fraunhofer Institute for Machine Tools and Forming Technology have created a light-blocking facade for such windows that only kicks in when exposed to strong sunlight – and it's powered by that sunlight, too.

The facade was developed via a collaboration between Fraunhofer and the Weissensee School of Art in Berlin.

Based on a concept by design student Bára Finnsdottir, it's composed of an array of circular flower-like components. Each one of those components contains a disc of fabric, with wires made from a nickel-titanium alloy running through it. That alloy is a shape-memory material – this means that although it will stay in a shape that it's been bent into when temperatures are cooler, it will temporarily revert to its original shape when heated.

In the case of the facade, that heat comes from direct sunlight. When that light heats the wires, they respond by reverting to a shape that draws the fabric discs closed, thus keeping the light from getting through the glass. Once the sun goes down or clouds roll in, however, the wires return to their previous shape and the discs open back up, making the facade transparent once again.

According to Fraunhofer, the facade could be retrofitted to existing windows, either on the surface of the glass or between the panes (in the case of double-paned windows). The light-blocking components could be made in a variety of shapes and sizes, while the complete facades could also be made to only cover a specific part of a window, if that was all that was needed.

Led by André Bucht, the researchers are additionally exploring the possibilities of using the facade to store thermal energy during the day and then release it at night, or to generate electricity via flexible solar cells.

A working prototype of the technology will be on display from Apr. 13 to 17, at the Hannover Messe industrial trade show.

Source: Fraunhofer