Freeform beam-down secondary concentrators for heliostat fields

We introduce a new type of secondary concentrator for solar towers, utilizing a freeform reflector in a beam-down setup to significantly enhance concentration ratios. By optimizing the reflector's shape and the heliostat aiming strategy, our designs approach aplanatic conditions, doubling to tripling concentration ratios while maintaining a significant gap between concentrator and receiver unlike existing CPC secondary concentrators. The compact design allows a multi-MW solar field to share a single secondary concentrator and receiver aperture. We show simulations of and example design for the 2.5MWth SSPS-CRS heliostat field in Almeria, Spain, demonstrating a secondary concentrator not larger than the existing tower. Furthermore, we discuss implications this type of concentrator has for heliostat field design, both in terms of heliostat size and field layout.