more on selective absorbers

Almeco-TiNOX makes a great selective absorber. it absorbs most sunlight – ’95 % of incident light’ and radiates very little in the infra-red – ’4 %’,  so that around ’90% of the solar energy can be used as heat’

TiNOX is a ‘hi-tech’ selective absorber made of multiple layers, with a quartz anti-reflection coating. it is made using computer controlled process equipment including vacuum chambers and Chemical Vapour Deposition equipment

there are other, simpler, selective absorbers. Dr. Md. Golam Mowla Choudhury from the
Department of Physics, University of Rajshahi, Bangladesh, in his succinct paper titled ‘Selective Surface for efficient Solar Thermal Conversion‘ describes several of them

Dr. Choudhury summarizes the desirable properties  of a good selective absorber:

  • high sunlight-emissivity at 0.2 – 2 microns, low emissivity for greater wavelengths, with sharp transition between the two spectral regions
  • stable opto-physical properties over long term operation at elevated temperatures, repeated thermal cycling, air exposure, ultra-violet radiation
  • if it is a coating (and he talks about several coatings), good adherence to substrate
  • coating must be easily applicable
  • and finally, absorber must be economical and affordable

absorbers such as copper oxide, nickel black, black chrome and cobalt oxide are listed. while these earlier known selective absorbers may not perform as well as TiNOX, they, and others of their kind, are worth a good look, because they may be simple, relatively easy to make and cost effective


About Vishwa Narayan

who can live without water? drinking water for all is my goal, through Theertham, a not-for-profit organization i founded and registered in Texas. you can reach me at
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