Ever since they were invented, windows have illuminated domestic interiors, adding to their unique atmosphere. This solution has always come at the cost of heat and energy loss, but perhaps this problem has finally been solved
Even today, in the English word “window”, meaning simply window, you can hear the linguistic residue of the protoplast of this invention. “Wind holes” means “windy openings,” which provided fresh air and also let a little light into the interiors of primitive huts. The energy balance of such a solution was obviously very poor, so before glass became popular and cheap, such holes were extremely small. The Romans were the first to come up with the idea of inserting a glass pane in the wall of a building, but it was not popularized in England until the 17th century. Today, this invention has a chance to go to an even higher level – to become a small power plant.
Thanks to double glazing of windows, unwanted air flow disappeared. Nevertheless, much of the heat energy still escaped through this modern invention by old standards. Although such windows occupied on average only ten percent of the insulated, outer shell of a building, they accounted for almost half of the heat lost. New technologies used in recent years have greatly improved this result. Today, glass has special low-emissivity coatings, and the window construction itself can be based on double-glazed units, among other things. As a result, manufacturers achieve high light transmittance and can produce windows with a larger surface area while maintaining maximum energy savings
Also important is the installation method, which has changed over the years. Improperly performed sealing of the wall-window joint weakens the insulation layer and leads to thermal bridges. Professionally applied layered installation includes the organization of three zones: the inner vapor-proof, the middle thermal insulation and the outer vapor-permeable. Vapor barrier tapes are responsible for the inner and outer parts, and polyurethane foam or mineral wool forms the middle layer. Despite all these complicated technologies, there is no way to completely eliminate heat loss. Unless the glazing itself becomes a kind of small power plant and balances the energy losses. In a passive house, the glazing lets light into the building, but additionally uses solar energy for its own purposes. A well designed building with high quality windows can even achieve a positive energy balance
There is a team at Michigan State University that developed a small, transparent solar cell in 2017. The researchers, led by Richard Lunt, aimed to create an entire pane of glass that could be successfully installed in a window frame. The glass skyscrapers of the big city could become huge solar power plants, generating energy exactly where it was needed most. The transparent solar cell was a remarkable invention, because it solved a difficult problem – how to use the energy accumulated in a beam of light without blocking its further path. Photovoltaics transforms the spectrum of light into electricity, and the human eye no longer has a chance to catch the waves collected by classical solutions. Translucent solar cells use only part of the spectrum to generate energy, the rest is passed on in the form of dimmed or colored light
What was an absolute novelty in 2017, today is a product that can be purchased and used in your own home. Through the high price and still not much efficiency, this technology is not yet widespread, but it is certain that the near future will bring a significant development in this field. Quantum dots are one of the most popular research trends. These are semiconductors invisible even under an optical microscope, with dimensions ranging from a few to several nanometers
This solution is extremely efficient but very difficult to produce. Therefore, specialists rely more often on carbon nanotube and perovskite technology. The glass made in this technique is supposed to be similar to the classic one, but in case of a large amount of sunlight it will darken, letting only about 3% of light through, replacing the blinds. The energy generated in this way will be stored and released during cloudy weather, when the glass regains its transparency again. Although researchers are still working on the ideal solution, developers are already using fully commercial products in office buildings where entire walls are made of glass. Windows made of crystalline silicon crossed with photovoltaic panels are used wherever covering part of the glass is not a problem. This solution, although not particularly aesthetic, is extremely efficient.
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