Editing Selective surface (section)

== Materials ==
Normally, a combination of materials is used.  One of the first selective surfaces investigated was a semiconductor-metal tandem<ref name=":0">{{Cite web|url=https://www.nrel.gov/docs/fy02osti/31267.pdf|title=Review of Mid- to High-Temperature Solar Selective Absorber Materials|last=Kennedy|first=Cheryl|date=2002|website=NREL|accessdate=21 February 2018}}</ref> – simply [[copper]] with a layer of black [[cupric oxide]]. Silicon on metal is also another example.<ref name=":0" /> A different design has ceramic–metal composites ([[cermet]]s) on metal substrates.<ref name=":0" /><ref>{{Cite journal|last1=Tesfamichael|first1=Tuquabo|last2=Wäckelgård|first2=Ewa|date=1999-07-01|title=Angular solar absorptance of absorbers used in solar thermal collectors|url=https://www.osapublishing.org/abstract.cfm?uri=ao-38-19-4189|journal=Applied Optics|language=EN|volume=38|issue=19|pages=4189–4197|doi=10.1364/AO.38.004189|pmid=18323901 |issn=2155-3165|bibcode=1999ApOpt..38.4189T|url-access=subscription}}</ref> [[Black]] [[chromium]] ("black chrome") and [[nickel]]-plated anodized aluminum is another selective surface that is very durable, highly resistant to [[humidity]] or [[oxidizing]] atmospheres and extreme [[temperature]]s, while being able to retain its selective properties, but expensive. One of the more popular designs – a multi-layer broadband solar absorber – consists of a metal substrate coated with multiple layers of metal and dielectric materials. While those have to be vacuum-deposited, they have been widely adopted due to their suitability for vacuum tubes.<ref>{{Cite web|url=http://www.almecogroup.com/en/pagina/53-tinox-energy-cu|title=TiNOX energy|last=|first=|date=2018|website=Alemco|accessdate=21 February 2018}}</ref><ref name=":0" /><ref>[https://supergreensolutions.com Renewable Clean Energy], 23 January 2023</ref>

Although ordinary black paint has high solar absorption, it also has high thermal emissivity, and thus it is not a selective surface.

Typical values for a selective surface might be 0.90 solar absorption and 0.10 thermal emissivity, but can range from 0.8/0.3 for paints on metal to 0.96/0.05 for commercial surfaces. Thermal emissivities as low as 0.02 have been obtained in laboratories.<ref name=":0" />