The concept of salt gradient is utilised to store heat energy in which of the following solar energy collecting systems?

A solar pond uses a salt gradient so that dense salty water at the bottom traps and stores heat.

The heavy brine layer cannot rise by convection, letting the base reach high temperatures.

Solar thermal collectors gather heat on a surface but do not rely on a salt gradient to store it.

Solar cells convert light directly into electricity and store no thermal energy this way.

A solar furnace concentrates sunlight with mirrors to reach very high temperatures, not by salinity layering.

The stored low-grade heat of a solar pond can drive turbines or provide space heating.