Optical properties of liquids for direct absorption solar thermal energy systems

Todd P. Otanicar, Patrick E. Phelan, Jay S. Golden

Research output: Contribution to journalArticlepeer-review

397 Scopus citations


A method for experimentally determining the extinction index of four liquids (water, ethylene glycol, propylene glycol, and Therminol VP-1) commonly used in solar thermal energy applications was developed. In addition to the extinction index, we report the refractive indices available within the literature for these four fluids. The final value reported is the solar-weighted absorption coefficient for the fluids demonstrating each fluid's baseline capacity for absorbing solar energy. Water is shown to be the best absorber of solar energy of the four fluids, but it is still a weak absorber, only absorbing 13% of the energy. These values represent the baseline potential for a fluid to be utilized in a direct absorption solar thermal collector.

Original languageEnglish (US)
Pages (from-to)969-977
Number of pages9
JournalSolar Energy
Issue number7
StatePublished - Jul 2009
Externally publishedYes


  • Fluids
  • Optical properties
  • Solar thermal energy

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • General Materials Science


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