Improved performance of open volumetric receivers by employing an external air return system

•An external air return system has been installed at the Solar Tower Jülich.•Parasitic losses of the fans are reduced by 34%.•A novel tracer gas technique has been employed to measure the air return ratio.•A reduction of the air return ratio under part load conditions was observed. 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.