Experimental performance of an advanced metal volumetric air receiver for Solar Towers

Kurzfassung

Solar Tower Technology is a promising way to generate sustainable electricity from concentrated solar radiation. In one of the most effective variants of this technology, a so called volumetric air receiver is used to convert concentrated radiation into heat. This component consists of a high temperature resistant cellular material which absorbs radiation and transfers the heat to an air flow which is fed from the ambient and from recirculated air. It is called volumetric, because the radiation may penetrate into the “volume” of the receiver through the open, permeable cells of the material. In this way a larger amount of heat transfer surface supports the solid to gaseous heat transfer in comparison to a tubular closed receiver. Finally the heated air is directed to the steam generator of a conventional steam turbine system. In this study an advanced cellular metal honeycomb structure has been designed, manufactured and tested for use as an open volumetric receiver. It consists of winded pairs of flat and corrugated metal foils. The technology is based on a one which has been primarily developed for the treatment of combustion engine exhaust gases. A number of variations of the pure linear honeycomb structure have been introduced to increase local turbulence and radial flow. Firstly, a set of samples has been tested in laboratory scale experiments to determine effective properties and the solar-to-thermal efficiency. After that, results have been compared with theoretical predictions. Finally, the three most promising materials have been used for a 500 kW test on the research platform of the Solar Tower Jülich. Air outlet temperatures of more than 800 °C have been achieved with efficiencies of about 80%, which is about 5% more than the state-of-the-art technology, which is currently used at the main receiver of the Solar Tower. Next to this, lifetime models will be developed to increase the overall reliability of the technology.