The sun is an abundant source of clean energy. Solar power is globally already the third largest source of renewable energy after hydro and wind power, and is growing exponentially. Solar panels are getting cheaper and appearing on the roofs of more and more buildings everywhere.
However, the future of residential solar energy is not in houses fully covered in solar panels, but rather in so called building integrated photovoltaics. This means that Instead of installing separate solar panels on every rooftop, buildings are constructed of elements that directly collect solar energy by themselves. Already on the market there are roof tiles, wall facades and skylights that produce electricity from sunlight.
In our Inno Indigo project, called Window integrated solar collector (WISC), we are developing windows that collect solar energy. Since the purpose of windows is to be transparent and let light in, we naturally cannot harvest the visible light. Luckily for us, more than 50% of sunlight comes in the form of infrared light, i.e., as a light with wavelength longer than in the visible light. This invisible light is also known as thermal radiation, and it tends to heat up the buildings which is often not desirable - especially in warmer climates. This further means that if we can collect the infrared light on the window already, it does not penetrate into the interior of the building and heat it. Thus, we can also save on the air conditioning costs, in addition to the energy collected.
As practically every building has windows and many modern architecture is in love with fully glass facades, the potential of solar windows for producing clean energy is huge. Unsurprisingly, many companies have also noticed this and are trying to cash in on this. Various ideas are being developed, such as organic photovoltaic solar arrays (Solar Window Technologies), luminescent solar collectors (Ubiquitous Energy), and transparent silicon (Onyx Solar, Polysolar), gallium arsenide (NanoFlex Power) and micro spherical (Sphelar Power) solar cells.
Although progress in solar windows is at a rapid phase, all existing solutions have severe problems with transparency, durability, efficiency or cost. Our idea is to use so called plasmonic resonances appearing in metal nanoparticles, for guiding solely the infrared light to the edges of the window, where it would be collected as heat or electricity. The basic idea has already been experimentally demonstrated by our intercontinental team of research groups. If we are successful in further development, the produced windows would be highly transparent, very durable and cost-effective to fabricate.
The anticipated challenges require experimental and theoretical expertise in various photonic and nano technologies as well as other related fields. To take up this gauntlet, we have formed a multinational consortium including researchers from Finland, Norway, Germany and India. Especially in India with its hot climate our ideas of reducing the heat load on buildings have been met with enthusiasm.
We are excited to be a part of the global sustainable energy revolution!
Text: Jussi Toppari