Solar Central Receiver
This type of solar energy device is also known as a solar power tower and uses much less land than the solar trough system described earlier.
The system consists of an arrangement of mirrors which concentrate their reflection of solar energy on a tank holding a heating medium.
The tower can be constructed from tubular steel members in an open lattice assembly, or concrete/steel design. They can be over 100m high and need to be well fixed onto concrete foundations.
The Heliostats (Mirrors)
The mirrors are flat as opposed to the curved mirrors normally associated with solar power. They are now arranged in groups on a common support arm so that a single controller can be used to adjust the orientation to follow the movement of the sun.
In some of the older types of arrangements, the mirrors were mounted on the ground as single units which necessitated the use of individual controllers.
The absorber in this case is a circular vessel enclosed in a solar radiation collecting material (ceramic honeycombed) into which the solar energy reflected from the mirrors is concentrated, heating the air inside the tank.
The Heating Medium
Several types of vapors and liquids can be used as heating mediums. A successful type is molten salt, which as well as supplying instant heat, can store the heat for use at night.
We shall use ambient air (a relatively new innovation) as the heating medium in our example of the technology. The air is heated to above 700 Deg C and ducted to an exchanger where it transfers its heat to water.
Steam Generating System
The heated air is drawn from the absorber by a fan and discharged through a heat exchanger. The heated air transfers its heat to the water which flashes off into superheated steam (400DegC) in an expander pressure vessel. The steam is used to drive a conventional steam turbine power generator.
The steam exits the LP stage of the turbine into the condenser where the resultant condensate pumped back into the heat exchanger water inlet in a closed circuit.