A solar evaporation pond is a saltwater pool that can be used to produce and store thermal energy. Such saltwater ponds form a natural vertical “salinity gradient,” known as a halocine. In these ponds, lower-salinity water floats to the surface, while high-salinity water remains at lower depths. The process is relative simple, and has been highly effective in generating electricity in rural areas of developing countries. Solar rays heat the water at the bottom of the pool, making it less dense than the water above it, and a process known as convection occurs naturally. Salt is added to solar ponds to saturate the lower, warmer water which can reach temperatures up to 90 degrees centigrade. Upper layers of low-salinity water, with much lower ambient temperature, do not mix readily with the hot, high-salinity water, which is then pumped out to be used in a turbine to generate electricity or as a source of cost-effective thermal energy.
A naturally occurring form of solar pond was discovered in the 1940s at Medve Lake in Transylvania in Hungary, sparking intense interest in the scientific community, and leading to extensive research and development focused on the viability of power generation not reliant on fossil fuels. Other natural solar ponds exist in the Atacama Desert Plateau of South America, situated between the Pacific Ocean and the coastal range of mountains. The first successful used of a solar pond to generate electricity was the Israeli Beit HaArava pond, which was operated on the West Bank until 1988. India established a solar pond at Bhuj, in Gujarat, which was completed in 1993 and operated successfully until the year 2000 when its sponsoring dairy development corporation suffered major financial losses. The pond was later declared non-functional due to an earthquake. The first salt-gradient solar pond in the United States is located in El Paso, Texas, and supplies 20% of the Bruce Foods Corporation’s power.
