a b s t r a c tA selection of granular natural and ceramic materials has been experimentally characterized with regard to their application as heat transfer and storage media in concentrating solar power plants. Thermophysical, thermomechanical, tribological and rheological measurements have been conducted in order to identify the most suitable candidates for this dynamic high temperature operation. Ceramic materials are found to comprise some advantages, but natural products offer a considerably more economic solution. Thermal bulk conductivity is found to be only marginally affected by the solid's thermal conductivity, while specific heat is the same for all solids. Ceramics entirely withstand thermal cycling, while quartzcontaining materials are prone to severe degradation. Most materials are found to attain a saturated state of attrition while being sheared under load, wherein quartz sand offers the lowest mass fraction of debris at saturation level. In the investigated grain size range, all materials show good flowability. The generation of debris requires consideration in the design of the CSP storage components.

In solar central receiver power plants open volumetric receivers using air as heat transfer fluid are an alternative to the currently predominant receiver types, namely salt and steam receivers. In order to improve their competitiveness, the receiver performance has to be improved. In the current study an external air return system has been integrated in the Solar Tower Jülich and its influence on power plant performance has been investigated. With this system, the parasitic losses caused by the fans are reduced by up to 34%. The measured air return ratio is mostly unaffected, but the current data suggest, that the internal and external convective losses of the receiver are reduced when an external air return system is applied. A positive influence of the total mass flow on the air return ratio has been identified for the current data while other parameters like the return air temperature turned out to be less significant.

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Heat storage based on particulate materials is a promising option to provide a demand-oriented electricity production with utility-scale solar power plants. For energy storage discharge, a moving bed heat exchanger is considered and its design is investigated. As a basis for a flexible design tool, a multiphase model based on the Eulerian continuum approach was set up to describe the bulk flow and the thermal performance. The model was applied to an example heat exchanger layout, and the simulation results were compared with an empirical model, confirming the validity of the approach. Initial parameter variations identify the key parameters and their effect on the thermal performance.