Solar Thermal Power Plants - Renewable Energy: Technology, Economics and Environment - page 225

- The working fluid of the thermal engine flows through tube bundle heat ex-
changers installed within the storage zone of the solar pond, and is thereby
heated up.
- The hot brine can also be pumped from the storage zone by means of an intake
diffuser, subsequently be transmitted to the working fluid of the thermal engine
and eventually be re-supplied to greater depths of the pond by another diffuser,
once the brine has cooled down. The technical approach allows adjusting the
position of the intake diffuser to the depth of the highest temperature. Sec-
ondly, heat losses by the pond bottom are reduced, since the cooled water is re-
cycled to the pond near the bottom.
As a matter of principle, a sufficiently dimensioned heat exchanger unit results
indispensable for the successful operation of a solar pond. Especially in times of
high radiation (i.e. at noon) it has to be ensured that heat can securely be with-
drawn from the pond, to prevent phase changes and/or make stratification insta-
ble.

Thermal engine. To convert solar thermal energy into mechanical and afterwards
in electrical energy, usually ORC processes are applied (see Chapter 5.1.4 and
10.3). These are basically steam cycles which utilise a low-boiling, generally or-
ganic, cycle fluid. Such processes permit to provide electrical energy also at low
useful temperature differences.

5.6.1.2 Plant concepts

Fig. 5.34 shows the general structure of a solar pond power generation plant. Ac-
cording to this graphic, the water absorbs the incident direct and diffuse radiation,
similar to the absorber of a conventional solar collector, and is heated up. The
technically adjusted salt concentration prevents natural convection and the result-
ing heat loss at the surface due to evaporation, convection and radiation.

Solar radiation

Generator

Hot water
cycle

Turbine G

Steam
generator

Solar po nd

Cold water

Transition zone
Hot water

Condenser

Cold w ater cycle

Fig. 5.34 Plant diagram of a solar pond power plant