Solar ponds are of two kinds which are convective and non-convective shallow ponds. solar ponds are a cheap solar collector for a long period of time storing and collecting thermal energy. Salt gradient pond is the most important type of non-convective ponds.
The salinity gradient solar pond is a steady reproduction pond of salted water where the salt concentration gradient rises as the depth increases in the pond. The salinity gradient solar pond contains of three layers. First and the upper layer is called the upper convective zone (UCZ), we find the temperature in the UCZ is equal to the ambient temperature and the salinity is approximately equal to the salinity of the sea water which is about 3.
3 wt% and the salt concentration is homogenous and convective heat transfer occurs. The second layer is called the non-convective zone (NCZ), conductive heat transfer happens and the salinity density and temperature increase quasi-linearly to attain the highest level, hence convection is not possible.