Selective surface: Difference between revisions
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In [[solar thermal collector]]s, a '''selective surface''' is a means of increasing it's operation temperature and/or efficiency. The selectivity is defined as the [[ratio]] of [[radiation]]-[[absorption]] (''alpha'') to radiation-[[emission]] (''epsilon''),. <!-- 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 emmissive radiation from the absorbing surface. |
In [[solar thermal collector]]s, a '''selective surface''' is a means of increasing it's operation temperature and/or efficiency. The selectivity is defined as the [[ratio]] of [[radiation]]-[[absorption]] (''alpha'') to radiation-[[Emission (electromagnetic radiation)|emission]] (''epsilon''),. <!-- 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 emmissive radiation from the absorbing surface. |
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Normally, a combination of materials is used. One of the first selective surfaces investigated was simply [[copper]] with a layer of black [[cupric oxide]]. [[Black]] [[chromium]] ("black chrome") [[nickel]]-plated [[copper]] 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. Another combination consists of [[steel]] plated with [[gold]], [[silicon]], and [[silicon dioxide]]. Ordinary [[steel]] or [[aluminum]] can also be [[Spray painting|spray-painted]] black for a cheaper (but less effective) collector surface. |
Normally, a combination of materials is used. One of the first selective surfaces investigated was simply [[copper]] with a layer of black [[cupric oxide]]. [[Black]] [[chromium]] ("black chrome") [[nickel]]-plated [[copper]] 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. Another combination consists of [[steel]] plated with [[gold]], [[silicon]], and [[silicon dioxide]]. Ordinary [[steel]] or [[aluminum]] can also be [[Spray painting|spray-painted]] black for a cheaper (but less effective) collector surface. |
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Revision as of 10:55, 25 June 2007
In solar thermal collectors, a selective surface is a means of increasing it's operation temperature and/or efficiency. The selectivity is defined as the ratio of radiation-absorption (alpha) to radiation-emission (epsilon),. Selective surfaces take advantage of the differing wavelengths of incident solar radiation and the emmissive radiation from the absorbing surface.
Normally, a combination of materials is used. One of the first selective surfaces investigated was simply copper with a layer of black cupric oxide. Black chromium ("black chrome") nickel-plated copper is another selective surface that is very durable, highly resistant to humidity or oxidizing atmospheres and extreme temperatures while being able to retain its selective properties - but expensive. Another combination consists of steel plated with gold, silicon, and silicon dioxide. Ordinary steel or aluminum can also be spray-painted black for a cheaper (but less effective) collector surface.
Typical values for a selective surface might be 0.90 absorption and 0.10 emissivity. but can range from 0.8/0.3 for paints on metal to 0.96/0.05 for commercial surfaces and emissivities as low as 0.02 have been obtained in laboratories.
See also
- Insulated glazing
- Solar box cooker
- Solar collector
- Solar oven
- Solar power
- Solar thermal collector
- Trombe wall
External links
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