Photovoltaic windows

The use of glass surfaces of buildings to insert photovoltaic systems can be very useful to pursue the objective of creating ZEB (Zero Energy Buildings), i.e. compliant with European directives 31/2010 and 27/2012.
Studies conducted at the University of Milano-Bicocca on nanoparticles capable of absorbing and emitting light, lead to overcoming the normal double-glazed window, which adds clean energy production to passive behavior. These studies have also been started at the CNR with the European consortium Citysolar and many universities, research centers and industrial partners.
Furthermore, some truly interesting solutions are coming onto the market. Photovoltaic glass, with almost no visual impact, is able to absorb solar radiation to transform it into electrical energy. This result is obtained thanks to photovoltaic cells made of a transparent gel, based on mono or polycrystalline amorphous silicon nanospheres with a yield of up to 100 Watts/mXNUMX; by inserting the gel on the surface of the glass, the light is absorbed and transformed into energy, with a production that can triple if the gel is inserted into the cavity of a double glazing unit. Between the cells and the glass there is also a layer of polyvinyl butyral (PVB), a plastic resin that blocks the glass in the event of breakage.

The glass could be inserted in the windows, with completely transparent solutions and, with various color effects and surface treatment characteristics, also for canopies, ventilated walls, and flush-to-the-roof windows.
Photovoltaic glass has a transparent appearance when the silicon film is particularly thin, a semi-transparent effect can be obtained by leaving empty spaces between the crystalline cells or by micro-perforations of the film through the laser while the photovoltaic cells block infrared solar rays and thermal radiation.

For glass walls, semi-transparent colored panels with an aluminum frame and a sandwich with a film made of organic solar cells composed of carbon-based semiconductor polymers and an external glass sheet can be used. Different types of organic cells offer different transparency to light, allowing you to evaluate the wavelength to filter, calibrating the desired transparency and the energy that can be generated.

Some solutions with prismatic optics filter diffused light by diverting direct sunlight towards the photovoltaic cells; the double glazing allows thermal insulation and blocks direct solar radiation, contributing to the energy saving of the building. The lighting inside the buildings is maintained, while the thermal characteristics of the windows improve.
Even though this is a technology that will offer further developments and solutions, there are already excellent proposals and possibilities for immediate use on the market.

Benefits

• Perfect integration into the architecture.
• Maintaining the characteristics of ordinary glass, ensuring up to 80% transparency.
• High cost-benefit ratio, thanks to energy savings.
• Possibility of insertion in any home, even for those homes in condominiums that do not have a roof on which to place photovoltaic panels and for homes subject to restrictions, such as in historic centers where the installation of photovoltaic systems on roofs is prohibited.

Disadvantages of photovoltaic glass

• Compared to a traditional system that can be oriented and tilted in relation to solar radiation, the efficiency is reduced since the glass is usually arranged vertically on the windows and there is not always good exposure to solar radiation.
• In a house with few glass surfaces and the impossibility of increasing the surfaces, the cost of the system may not be convenient. At present it can be applied in buildings with large windows, preferably facing south, with at least 200 square meters.