Page 129 - A Comprehensive Guide to Solar Energy Systems

128 A COmPREHEnSIVE GuIdE TO SOlAR EnERGy SySTEmS

FIGURE 7.1 Simplified scheme and main components of a Concentrating Solar Thermal Power System.

Solar concentrators are basically optical devices that are designed according to the
optical law that the incidence and reflection angles of a ray on a reflecting surface are
equal in value; the solar radiation impinging on a concentrator must arrive from a proper
direction to assure that it will go to the receiver after being reflected. Hence a very im-
portant limitation of CST systems is that they can only use direct solar radiation; diffuse
radiation is not effective as it propagates in all directions and can’t be concentrated in an
efficient manner.
The thermal energy gained by the working fluid at the receiver, in the form of sensible
and/or latent heat, is then either converted into electricity by means of a thermodynam-
ic cycle producing the mechanical energy required to drive the electricity generator or
sent to a thermal storage system to be used later to feed the thermodynamic cycle when
direct solar radiation is not available (i.e., overnight or during cloudy periods). Some
waste heat from the thermodynamic cycle is usually available as a by-product of electric-
ity generation.
The set of elements where the thermal energy delivered by the receiver is converted into
electricity is called the Power Block, which includes not only the thermodynamic cycle and
the electricity generator, but also the auxiliary components required for the thermodynam-
ic cycle to work (e.g., fluid circulation pumps, heat exchangers, and steam condensers).