Solar Thermal Power Plants - Renewable Energy: Technology, Economics and Environment - page 223

0.06 €/kWh for the 200 MW plant. Thus, the power generation costs decrease
significantly with increasing plant size.
The sensitivity analysis shows similar results as the analysis conducted for a
solar tower plant (Fig. 5.13).

Environmental analysis. Environmental effects of solar updraft tower power
plants are very similar to that of solar tower power plants. They are therefore dis-
cussed within the scope of Chapter 5.2.2 on solar tower power plants.

5.6 Solar pond power plants

Solar ponds are power plants that utilise the effect of water stratification as a basis
for the collector. A basin filled with brine (i.e. a water/salt mixture) functions as
collector and heat storage. The water at the bottom of the solar pond serves as
primary heat storage from which heat is withdrawn. The deeper water layers and
the bottom of the solar pond itself serve as absorber for the impinging direct and
diffuse solar radiation. Due to the distribution of the salt concentration within the
basin, which increases towards the bottom of the basin, natural convection and the
ensuing heat loss at the surface due to evaporation, convection and radiation is
minimised. This is why heat of an approximate temperature between 80 and 90 °C
(approximate stagnation temperature 100 °C) can be extracted from the bottom.
Thanks to suitable thermodynamic cycles (e.g. ORC process) heat can then be
used for power generation.

5.6.1 Technical description

In the following, the technology of solar pond power plants, including all related
components, is explained.

5.6.1.1 System components

As follows the main system components of a solar pond power plant are described
in detail.

Pond collector. Pond collectors are either natural or artificial lakes, ponds or
basins that act as a flat-plate collector because of the different salt contents of
water layers due to stratification. The upper water layers of relatively low salt
content are often provided with plastic covers to inhibit waves. This upper mixing
zone of such pond collectors usually is approximately 0.5 m thick. The adjacent
transition zone has a thickness of 1 to 2 m, and the lower storage zone is of 1.5 to
5 m thickness.