Using nanotechnology to make sustainable buildings greener, literally

During the past decades functional thin films have crept into our daily life, but so discreetly that they easily go unnoticed. To illustrate one of their uses, Dr. Schüler explains that when light shines through a typical double glazed window, it crosses not just one, but two such films, each with a thickness in the nanometer range. The inside of the outer window pane is coated to selectively allow the visible light spectrum to enter while at the same time filtering invisible wavelengths that would cause undesired overheating. The coating on the outside of the inner pane is designed to reflect warmth from indoors back into the building.

The thin films under development in Dr. Schüler’s group have a long list of potential applications for which the properties of different types of nano-structured materials are exploited. Glazed thermal solar collector modules that can be integrated into the facades of office buildings are one such application. Using these modules, energy can be extracted from the incoming solar radiation to heat, or even to cool, the rooms inside. Aesthetically, most thermal solar collector modules fabricated today leave much to be desired, and architects have been reluctant to include them into their projects. But with a combination of technology and design, they are being given a second chance. Using methods developed here, their usually transparent protective panes can be coated to appear glazed, colored, and opaque, hiding the unattractive solar absorber sheets behind them without excessively sacrificing their transparency to solar radiation. And, as emphasized by Andreas Schüler, thanks to their modern design, “they integrate perfectly into the skin of a building.”

Nano-structured coatings also find uses in increasing the efficiency of power generation using solar energy. Solar thermal power plants harness energy from solar radiation to produce steam that drives turbines coupled to power generators, ultimately producing electricity. Solar energy is captured by focusing incoming sunlight on black steel tubes carrying a fluid using parabolic trough shaped mirrors. Apply the right selective solar absorber coating to the steel tubes and you increase the electricity generated, pushing down its price to highly competitive levels. The coatings made using a novel approach developed in the group are much more durable than similar ones made using traditional approaches and have demonstrated that they can withstand high levels of solar radiation absorption over long durations, even at temperatures of 360 - 500 °C to which they are frequently exposed.

Discoveries in nanotechnology abound, and, at least from outside, it seems like their applications are limited only by the scientist’s imagination. Solutions can be tailored to address very specific problems. Right now, scientists are working on thermochromic coatings: using a switchable optical coating, black surfaces can capture incoming solar radiation to very high efficiency until a critical temperature is reached. Crossing this temperature threshold triggers a transition in the optical properties of the coating. In the case of solar thermal collectors, this behavior can be exploited to automatically regulate the solar energy uptake and protect the system from overheating. Another ongoing project involves the development of a surface treatment for windows to deflect incoming light deep into rooms in an approach analogous to a more invasive method previously developed at LESO-PB. The virtues of improved propagation of natural light into office spaces have been studied and discussed in the media.

These are only some examples of projects that are underway under Dr. Schüler’s supervision. Besides their scientific and entrepreneurial ingenuity, the projects in his research group share the notion of looking for applications for discoveries made in basic research in the field of nanotechnology. Having realized that it isn’t enough to come up with a laboratory scale prototype of an application - you have to go all the way and develop manufacturing processes that can be used at commercial scales for the application to stand a chance of being taken up successfully by the industry - it has become a principle to work hand in hand with companies to help them develop manufacturing processes. As a case in point, the solar collector modules described above are being commercialized by SwissINSO, a company based in the EPFL Science Park, with whom Andreas Schüler’s group has a technology transfer mandate.

EPFL's interdisciplinary laboratory of Solar Energy and Building Physics LESO-PB is directed by Professor Jean-Louis Scartezzini, and hosts engineers, architects, photobiologists and physicists. Nanotechnology became an additional center of competence through the work of Andreas Schüler, and over the years, led to the establishment of his research group within LESO-PB. Bridging abstract findings in theoretical research and concrete real world applications seems to be a passionate pursuit to him and his team. “Our students are very motivated to work on scientific research related to renewable energies”, says Andreas Schüler, who’s students and staff managed to stay upbeat and keep up their team spirit despite the extra workload caused by the move.