Salinity gradient solar ponds - Solar Energy Sciences and Engineering Applications - page 210

Figure 7.4.2 50m 2 solar pond at RMIT University, Melbourne,Australia.
a wall around 1.2 m above the ground. As the pond wall is partially above the ground
level, it allows using a gravity assisted overflow system to maintain the level of water
in the pond. Salt lost by diffusion is replenished by adding solid sodium chloride salt
to the bottom of the pond with a cylindrical salt charger (Andrews and Akbarzadeh,
2005; Leblanc et al., 2011; Yaakob et al., 2011).
The diffused salt that reaches the top convective zone must be removed to maintain
the salinity gradient; at RMIT solar pond the top surface of the pond is continuously
flushed with low salinity water, and this helps to remove the diffused salt. The flow
rate of flushing should be kept at around twice the local yearly average evaporation
rate. To reduce stirring of the top convective zone by natural wind, 0.6 m diameter
floating rings made from high density polyethylene are spread over the top surface of
the pond; these rings help reduce the amplitude of the waves formed due to natural
wind. At present, the clarity of the water in this solar pond is maintained by keeping
the pH in the range of 5 to 6.
Figure 7.4.3 shows the 3000 m 2 solar pond designed and constructed by RMIT
University along with two industrial partners in early 2000 for supplying heat for salt
drying process at Pyramid Salt Factory (Akbarzadeh et al., 2005). This pond has a
total depth of 2.3 m, with a storage zone that is 0.8 m thick and a gradient zone of
about 1.2 m. Initially this pond mainly supplied heat for the process of salt drying while
later some amount of heat was also supplied to an aquaculture farm on the factory
site. Saline ground water is used for surface flushing and the water that overflows is
carried to a large evaporation pond. The location of the pond was around 200 m from
Pyramid Hill's salt production plant. Unfortunately after the flash flooding in part of
Victoria, Australia, the salt production facility was relocated and the solar pond is not
in operation anymore.
7.4.3 Solar ponds - USA
In 1983 the University of Texas at El Paso along with Bruce Foods, Inc., constructed
a 3700 m 2 solar 20 km northwest of El Paso city centre as shown in Figure 7.4.4 (Lu
and Sandoval, 1993; Akbarzadeh et al., 2005). Through well-designed procedures for