Asymmetric secondary reflectors for multi-stage solar tower plants

We present asymmetric secondary reflectors made of plane facets for increasing the concentration of radiation from a field of heliostats. The reflectors are suited for partitioning the receiver in several parallel units. In the case of an asymmetric directional distribution of the radiation intercepted by the secondary reflector, asymmetric reflectors may significantly increase the concentration compared to their symmetric counterparts. Best results are obtained with reflectors based on rectangular entrance and exit apertures, without constraint on the shape of the exit aperture. For the example presented, the concentration may be increased by 90% under the constraint of an optical efficiency of 90%. Even if the shape of the exit aperture has to be close to circular, asymmetric reflectors based on hexagonal apertures may obtain 30% improvement in concentration.