Solar Thermal Power Plants - Renewable Energy: Technology, Economics and Environment - page 171

already state-of-the-art technology. Due to this, within the following sections,
only the solar-specific part of such power plants is discussed in detail.

5.1 Principles

Basically, the process of solar thermal power generation is realised within the
following steps:
− concentrating solar radiation by means of a collector system;
− increasing radiation flux density (i.e. concentrating of the solar radiation onto a
receiver), if applicable;
− absorption of the solar radiation (i.e. conversion of the radiation energy into
thermal energy (i.e. heat) inside the receiver);
− transfer of thermal energy to an energy conversion unit;
− conversion of thermal energy into mechanical energy using a thermal engine
(e.g. steam turbine);
− conversion of mechanical energy into electrical energy using a generator.
Fig. 5.1 illustrates the general energy conversion chain of such a solar thermal
power generation plant. Selected aspects of this kind of solar energy conversion
are discussed below.

Conversion of
solar energy
inside the
receiver and
transmission to
a heat transfer
medium

Conversion of
thermal ener-
gy inside the
heat transfer
medium into
mechanical
energy

Collection and
concentration, if
applicable, of
radiation energy in
the collector

Conversion of
mechanical
energy into
electrical
energy

Grid

Thermal
energy
in the heat
transfer medium

Mechanical
energy
in the thermal
engine

Electrical
energy
inside the gene-
rator or the grid

Radiation energy
of the sun

Fig. 5.1 Energy conversion chain of solar thermal power generation

5.1.1 Radiation concentration

Radiation concentration is necessary if higher temperatures than those generated
by flat-plate collectors are required. The concentration of solar radiation is de-
scribed by the concentration ratio. It is defined according to two different meth-
ods:
- On the one hand, concentration ratio C can be determined solely geometrically
( C geom ), describing the ratio of the solar aperture surface A ap to the absorber sur-
face A abs (Equation (5.1)); also, the explanations within this chapter are based