Electrically heated glass was first developed in World War II to prevent aircraft windscreens from frosting over and obscuring visibility. Since then, this technology has been become almost universally used in aviation. It has even reached supermarket freezers, where glass doors must remain clear for customers to be able to see the merchandise. In order to electrically heat glass, a microscopic Tin (II) Oxide coating is applied to a pane of ordinary float glass. This coating is perfectly transparent and conducts electricity. An electrical current is supplied by two busbars located on opposite sides of the glass. The electrical resistance of the Tin Oxide coating produces heat energy. This heat radiates from the glass in the form of infrared energy. The busbars are typically connected to a power control unit that regulates the flow of electricity and thus the temperature of the glass, much the same as your backlite defogger/defroster system.
Electrically heated glass maintains a steady and consistent temperature across the entire surface, and heat radiates off the glass in only one direction: toward the object or area to be heated. In addition, this technology imparts beauty and elegance to glass. The glass can also be coloured or etched with designs in order to complement the appearance of a room or appliance. At one time the Corvette looked at having the grid pattern created to look like the Chevy ‘Bow Tie” symbol.
Electrically heated glass is a laminated glass, incorporating almost invisible electrically-conductive wires. It comprises two or more sheets of glass interlaid with one or more films of polyvinyl butyral (PVB). This assembly combines comfort with safety, whilst preventing condensation. Electrically heated glass is suitable for any circumstance where there is high moisture content in the air and where the difference between the internal and external temperature may lead to condensation risk. In heatable glass, invisible wires or an invisible metallic coating, in each case embedded into the interlayer of the laminated windscreen, respond to an electrical charge by raising the temperature of the glass, in cold weather speeding the removal of any condensation or ice and then of course preventing any further condensation or ice buildup. The potential failure mode to embedded wires is moisture intrusion and delamination. Depending on how quickly the elements heat up, there is always a risk of thermal shock which could lead to windshield a failure mode.
Today's increased use of glass in automobiles means that, without the right technologies, more solar energy will penetrate the interior of the vehicle, causing high temperatures. For example, when the outside temperature is 80.6°F/27°C, without anti-heat technologies, a car interior can heat up to 136.4°F/58°C in few minutes. Combating this solely by way of air-conditioning alone would be an environmentally unfriendly approach, leading as it would to higher fuel consumption and CO2 emissions.
In recent years, the industry has developed solar control glazing. This type of glass is specially engineered to reduce vehicle cabin by up to 44.6°F/7°C or 46.4°F/8°C temperature, and reduce heat penetration in vehicles exposed to solar radiation by over 25%. In this way, a significant amount of energy is saved from powering air-conditioning units while passengers' comfort is safeguarded.