Experimental and numerical investigation of volumetric versus surface solar absorbers for a concentrated solar thermal collector

The analysis revealed that the vacuum-packaged volumetric receiver had an efficiency of 54% and 26% operating at 80 °C and 200 °C, respectively. This lower than a vacuum-packaged black chrome-coated receiver, which had an efficiency of 68% and 47% in the same concentrator, operating at the same temperatures, respectively. [Note that commercial linear concentration systems typically have efficiency in the range 44-57% at 200 °C.] The inferior performance of the volumetric receiver was found to be due to higher reflective optical and radiative heat loss from the surface of glass tube. Overall, this study reveals that the proposed low-profile collector design is suitable for utilisation in industrial and commercial heating applications, but that volumetric absorbers will require anti-reflective and good selective coatings to be competitive with surface absorbers. If these challenges can be overcome, nanofluid receivers may have a cost/manufacturing advantage since glass-to-glass vacuum sealing is easier to achieve than metal-to-glass.