This photo displays a large scale salt gradient solar pond at the University of Texas at El Paso developed by John Walton and Andrew Swift. A solar pond is a body of water that collects and stores solar energy. Solar energy warms bodies of water exposed to the sun, but the water loses its heat unless some method is used to trap it.
Water warmed by the sun expands and rises as it becomes less dense.
Once it reaches the surface, the water loses its heat to the air through convection, or evaporates, taking heat with it. The colder water, which is heavier, moves down to replace the warm water, creating a natural convective circulation that mixes the water and dissipates the heat. The design of solar ponds reduces either convection or evaporation in order to store the heat collected by the pond. They operate in almost any climate. Convecting or Saltless Ponds A well-researched example of a convecting pond is the shallow solar pond.