Oculus de-concentrator

An oculus de-concentrator can be used to shield the boiler water wall from sunlight.

Shielding the boiler tubes from direct sunlight may require a de-concentrator, i.e., an optical device that decreases beam divergence. If this device is reflective, then it will be heated more by the sunlight than the thermal back-radiation. Being reflective, it can be actively cooled on its non-illuminated side. The heat balance is taken at the smaller, entry, aperture, so maximum concentration does not need to be increased. In the diagram the peak solar flux at the smaller entry aperture is 3960 kw/m2, 1960 kw/m2 at the exit.