A solar pond is a body of water that collects and stores solar energy.
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 can operate in almost any climate. Because the density of the brine increases with salt concentration, the most concentrated layer forms at the bottom.