An general source of water, ponds are very impotant and fundemental to man. They have been alterered and recreated to fit different needs and wants of man. They are an important factor in domestic, agricultural and recreational usages. Ponds, whether natural or man made, hold many deposits which have had an preserving effect on materials that naturally would have deteriorated over time. This is of great interest to paleo-enviormentailist. They are able to examine and study preserved matter that give much greater insight to the some aspects of the past. Modern day ponds can be utilized for agricultural usages in which water is retained and irrigated to moisten and fertilize the soil. Recreational usages include swimming, aesthetic design and fishing. Alot of commercial fisheries use ponds for thier easy availability. In addition there are solar ponds, which are designed to store solar energy.
Solar ponds are basically large soler thermal energy collectors. They are used for many reasons such as heating, solar power generation,desalination, refridgeration and drying. Solar ponds are saltwater sourses that forms vertical saline gradients of different concentrations. The bottom layer, which has the highest salinity, has high optical absorption and gets easily heated, increasing temperature and causing thermal expansion. The heat from the bottom layer can reach well over 90 degrees Celcius, levels three times that of the upper layer. The heat stored can be used for industrial hot water, heating buildings, Stirling engine for generating electricity and to drive an organic Rankine cycle. ( A Sterling engine operates by cyclic compression and expansion of air at different temperature levels so that there is a conversion of heat energy to work. Organic Rankine cycle uses liquid vapor phase changes and allows heat recovery from lower temperature sources.
Solar ponds are great for developing courntries because large area collectors are set up for a small price, the price of the pond liner. It also doesn't require a a seperate collector for thermal storage. The disadvantages include the fact that the evaporated water portions needs constant replenishment and removal of aslt crystals becomes expensive.