A smart window design from Friedrich Schiller University Jena in Jena, Germany, changes its light permeability at the A prototype of the innovative smart windows for controlled shading and solar thermal energy harvesting. Source: Jan-Peter Kasper/FSUA prototype of the innovative smart windows for controlled shading and solar thermal energy harvesting. Source: Jan-Peter Kasper/FSUtouch of a button and can also be used to harvest solar thermal energy. The switchable, ultrathin suspended particle device was developed for large-area integration with smart facades.

The researchers engineered new glass materials with embedded large-area channel structures for circulating functional fluids. The liquid is loaded with the nanoscale magnetic iron particles, which can be extracted with the help of a magnet or re-suspended by simply switching-off the magnet.

Depending on the number of the iron particles added, the liquid itself takes on different shades of grey or it will even turn completely black. This allows for the automatic adjustment of incident light or for the capture of solar heat. The efficiency in terms of heat gain per area is comparable with that of state-of-the-art solar thermal facilities, but the new system can be readily integrated in a vertical façade. Switching between on and off — the release or capture of particles — happens in a separate tank, without the need for an electrical connection.

In the fully shaded state, the researchers demonstrated a typical harvesting efficiency of 45 percent of the incoming solar power. For an average solar irradiance of 1,000 W m−2 during 800 h a−1, this corresponds to a solar thermal harvesting capacity in the range of 360 kWh a−1 m−2.

Such large-scale fluidic windows can substitute for air-conditioning and daylight regulation systems, say the researchers.

The study methods and results are published in the journal Advanced Sustainable Systems.

To contact the author of this article, email shimmelstein@globalspec.com