Two novel high-porosity materials as volumetric receivers for concentrated solar radiation

This article reports on two novel porous materials, which have been foreseen as volumetric receivers for concentrated solar radiation: a double-layer silicon carbide foam and a screen-printed porous silicon carbide material. Volumetric receivers are used in the solar tower technology. In this technology ambient air flows through the porous solid, which is heated by concentrated solar radiation. A heat exchanger then transfers the energy to a conventional steam turbine process. The general thermophysical and permeability properties of materials required for this application are reviewed. Experimental set-up and results of pressure loss and laboratory scale tests in concentrated solar radiation are reported. For the foam, efficiency data could be determined from the test results. Finally, a comparison is presented between the efficiency properties of the foam and those of materials used for the same application until now. This comparison shows, that the efficiency of the double-layer foam material is significantly higher. Up to now, porous materials consisting of a parallel channel geometry with thin walls showed disadvantageous permeability properties. By applying a new manufacturing process and modifying the channel geometry, the permeability properties of the printed material could be significantly changed, so that it now meets the requirements for an application as a volumetric receiver.