A new high temperature receiver (HT) module was developed for operation as third stage, extending the upper temperature limit of the pressurized receiver modules to 1000°C.
The receiver module consists of a receiver unit and a secondary concentrator. The secondary concentrator is installed in front of the receiver unit to further concentrate the solar radiation. The entrance aperture of the secondary concentrator is hexagonal, thus allowing a honeycomb-like arrangement of multiple receiver modules to scale-up power.
The receiver unit consists of a pressure vessel with an aperture, which is closed by a domed quartz window. Behind the window a ceramic absorber using multiple segments of a high porosity reticulated SiC foam, is installed. The absorber segments are integrated with a newly developed mounting structure based on thin fiber-reinforced ceramic sheets. Special attention was paid to the different thermal expansion behaviour of the components. A special absorber back layer is used to artificially increase the flow resistance through the absorber to achieve a more homogeneous mass flow distribution.
The highly concentrated radiation is absorbed in the highly porous foam structure and heats it up. The air is passing through the hot absorber and is effectively heated by convection.
A new window cooling technology was developed to ensure operation of the quartz window below its temperature limit. Air jets are directed towards the window and are operated in a special way to ensure good and homogeneous cooling of the window surface.
The HT- module was designed for operation as third stage of a serial connection of three receiver units, resulting in an air inlet temperature of about 750°C. In the solar tests during the project period, a maximum average air outlet temperature of 960°C was achieved, with good performance of the HT receiver module. A failure of the gas turbine stopped further testing, therefore the design temperature of 1000°C could not be achieved so far. Based on the obtained operation experience it is expected that in future tests the design temperature can be achieved.
A low temperature (LT) receiver module was developed for operation as first stage in the serial connection, with the goal of a significant cost reduction for the first stage. As the desired outlet temperature was not higher than 500°C, a design using multiple helically bent tubes was made. A number of 16 metallic tubes connected in parallel was bent in a way to form a cavity. The module was designed, manufactured and integrated into the system. For the advantage of low manufacturing cost a trade-off had to be made with pressure loss. For this receiver, the pressure loss is about 100mbar.
The cost predictions were refined based on the manufacturing data and the expected cost reduction of about 50% was verified.
The module was installed in the solar test bed, with a secondary concentrator in front of the unit. During the solar tests the receiver performed quite well, and the performance data is in good agreement with predictions.
Still missing is the long term experience with the receiver modules. The test time collected so far does not enable long term predictions of eventual degradation nor the definition of maintenance schedules.