Editing Selective surface (section)

{{Short description|Ordinary surfaces re-radiate heat they absorb. Selective ones re-radiate only a little.}}
{{More citations needed|date=July 2014}}
[[Image:Col·lectors solars de tub de buit.JPG|right|thumb|Solar thermal collector system based on evacuated glass tubes. Sunlight is absorbed by a special material at the center of each tube that has a selective surface. The surface absorbs sunlight nearly completely, and emits very little of the solar heat as thermal radiation. Ordinary black surfaces are also efficient absorbers, but they emit thermal radiation copiously.]]

In [[solar thermal collector]]s, a '''selective surface''' or '''selective [[Absorption (electromagnetic radiation)|absorber]]''' is a means of increasing its operation temperature and/or efficiency. The selectivity is defined as the [[ratio]] of [[solar radiation]] [[absorption (electromagnetic radiation)|absorption]] (α<sub>sol</sub>) to [[thermal infrared radiation]] [[emission (electromagnetic radiation)|emission]] (ε<sub>therm</sub>).

<!-- Materials that exhibit this combination of characteristics do not, however, exist in nature. -->Selective surfaces take advantage of the differing wavelengths of incident solar radiation and the emissive radiation from the absorbing surface:<ref>{{Cite web|last=|first=|date=|title=Absorbing Surfaces|url=https://www.impact-absorbing-surfaces.co.uk/|archive-url=|archive-date=|access-date=2020-11-26|website=www.impact-absorbing-surfaces.co.uk}}</ref>
* Solar radiation covers approximately the wavelengths 350&nbsp;nm to 4000&nbsp;nm; [[UV-A]], [[Visible light|visible]] and [[near infrared]]&nbsp;([[Near infrared|NIR]], or [[IR-A]] plus [[IR-B]]).
* Thermal [[infrared radiation]], from materials with temperatures approximately in the interval -40 to 100&nbsp;°C, covers approximately the wavelengths 4000&nbsp;nm to 40,000&nbsp;nm =&nbsp;4&nbsp;um to 40&nbsp;um; The thermal infrared radiation interval being named or covered by: [[Mid-infrared|MIR]], [[LWIR]] or [[IR-C]].