History of the solar ponds: A review study

Solar pond was discovered as a natural phenomena around the turn of the last century in the Medve Lake in Transylvania in Hungary. In this lake, temperatures up to 70 °C were recorded at a depth of 1.32 m at the end of the summer season. The minimal temperature was 26 °C during early spring. The bottom of this lake had a salt NaCl with concentration of 26 percent. Solar pond is artificially constructed. To prevent convection, salt water is used in the pond. Those ponds are called “salt gradient solar pond”. Nowadays, mini solar ponds are also being constructed for various thermal applications. It was concluded that the optimum value of salinity in the mini solar pond is 80 g/kg of water.