Real-time computation and control of solar flux density on a central receiver (Solar Two) (preheat)

The authors first briefly describe the effect that the added restriction of a maximum allowable flux density has on the design of the heliostat field. They then give a very brief description of a new computational procedure to actively defocus heliostats in case the allowable flux is exceeded. Finally, they discuss in some detail the problems involved in initiating salt flow in an ambient temperature molten salt receiver. The authors present a computational method for defining a set of heliostats to allow use of solar energy to preheat the dry receiver prior to initiating salt flow, along with significant details of its development and operation. While midday preheats are rather uneventful, the rapid increase in insolation and the improvement in heliostat performance in the early morning necessitates rapid action to avoid damage to the receiver. It is important to keep in mind the idea that Solar Two is a technology demonstration for a larger commercial system, and the techniques used here should be readily extended to commercial designs.