Solar Thermal Power Plants - Renewable Energy: Technology, Economics and Environment - page 187

threshold can be lowered by the use of molten salt and volumetric receivers in
particular.

1.20

1.00

0.80

0.60

0.40

0.20

0.00

0123456789 0 1

2

Direct radiation in kWh/(m d)

Fig. 5.10 Performance characteristics of Solar One

Solar Two. With the aim to solve the problems encountered with the Solar One
plant the latter was remodelled to the Solar Two plant. As heat transfer and heat
storage medium, molten salt consisting of 40 % potassium and 60 % sodium ni-
trate was applied. Thanks to the use of additional thermal energy storage the sys-
tem is more independent from the available solar radiation.
The functional principle of the Solar Two power plant is shown in Fig. 5.11.
Salt is pumped from a "cold" salt storage onto the tower and transferred from
there into the receiver, where it is heated by the reflected solar radiation. Subse-
quently, it reaches the "hot" tank. Hot salt, and thus energy is taken as needed
from the storage facility and pumped through a steam generator that generates
steam for a conventional steam turbine cycle. Afterwards, the salt cooled inside
the steam generator reaches again the "cold" salt storage.

Sun

Receiver

565 °C

Generator

Salt tank
(hot)

Turbine G

Steam
generator

Tower

290 °C

Heliostat

Salt tank
(cold)

Salt cycle Condenser

Fig. 5.11 Principle of the Solar Two power plant using molten salt as heat transfer and
heat storage medium (see /5-11/)