unglazed solar collector
An unglazed solar collector is a solar collector that consists of an absorber without the glass covering of a glazed flat-plate collector. In North America, unglazed flat-plate collectors currently account for the most area installed per year of any solar collector. Because they are not insulated, these collectors are best suited for low temperature applications where the demand temperature is below 30°C. By far, the primary market is for heating outdoor swimming pools, but other markets exist including heating seasonal indoor swimming pools, pre-heating water for car washes, and heating water used in fish farming operations. There is also a market potential for these collectors for water heating at remote, seasonal locations such as summer camps.
Unglazed collectors are usually made of black plastic that has been stabilized to withstand ultraviolet light. Since these collectors have no glazing, a larger portion of the Sun's energy is absorbed. However, because they are not insulated a large portion of the heat absorbed is lost, particularly when it is windy and not warm outside. They transfer heat so well to air (and from air) that they can actually capture heat during the night when it is hot and windy outside.