Solar glass is a type of window and building material that is designed to block radiant heat transfer, which is basically the amount of heat from the sun that passes through the glass and into whatever space is on the other side. This type of glass is most commonly used in the windows of office buildings and homes, though sometimes it is also used in automobiles and in industry, often in the panels of warehouses or machinery that is exposed to a lot of solar radiation. There are a number of different coatings that can be applied, each with its own specifications. Most are designed to reduce heat absorption and improve insulation, both of which can reduce energy costs.
In essence, solar glass is the combination of solar technology and standard window glass. Most of these windows don’t look any different form their more traditional counterparts; they’re just as clear and usually allow the same amount of light in. What they don’t usually allow in, or at least don’t allow as much of in, is radiation, which is the energy put off by the sun. This is achieved through an invisible coating that’s applied to the glass before it’s ever installed. Most of the time this coating is permanent and is designed to last for the life of the glass.
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Why They’re Used
This type of glass is usually designed to reduce heat loss but allow sunlight in for warmth, a concept also known as “solar gain.” There are a couple of reasons why this is important, but reduced energy costs are a big factor. Windows are an important source of natural light, but they can also be tough to insulate. The outside elements, be they hot or cold, often penetrate window settings much more easily than walls or doors, and a lot of this has to do with the permeability of the glass itself.
Glass that has been coated so as to maximize the sun’s energy can help a lot when it comes to energy retention, and these types of high-performance glass products are used across many industries. Recent advances in solar technology, at least where glass is concerned, include laminated products that boost solar power. This concentrating solar power (CSP) reflectivity provides efficiency and durability.
How They’re Made
Glass windows coated with a low-emittance (low-E) coating block radiant heat transfer. This lowers the amount of heat that passes through a window. Low-E coatings are nearly invisible, and are usually made up of layers of metal or metallic oxide on a glass surface.
Depending on energy needs, different types of low-E coatings allow for high, moderate, or low solar gains. In layered glazing, heat can be transferred between panes of glass, usually passing from warmer to cooler. Putting a low-E coated pane in the space between layers of glass helps block that heat. Window technologists in the past filled this gap with air or dry nitrogen.
Today, argon and krypton gas are most commonly used between panes, which has improved window performance. Both gases are nontoxic and nonreactive. Krypton is more expensive than argon, so some manufacturers combine the two gases to improve thermal performance at a more reasonable cost. Double-glazed windows with an argon gas fill between panes of low-E-coated glass are called pyrolitic, which means “hard coated.”
Glass with high solar gain is best suited to windows in cold climates. By contrast, low solar gain, or spectrally selective, low-E glazings are more beneficial for buildings and homes in warm climates. These products reduce heat loss in cold weather, yet also reduce heat gain in hot weather. Spectrally selective solar glass out-performs most tinted and reflective glazings. The level of visible light let in is usually high in proportion to the amount of heat reduction.
For climates that require both heating and cooling during different seasons, all levels of low-E coating can result in lower annual energy bills. Solar-optimized glass is practical for windows, doors, and skylights. Commercially, it is used for the top surfaces of thermal collectors and photovoltaic modules. Solar glass is almost always colorless, but in most cases it can be patterned for optimal solar energy transmission.