Widely accepted throughout the world, and suitable for tropical climates, free flow thermo siphon systems are automatic, simple, and reliable. Because the solar collector is positioned lower than the tank, the sun-heated water in the collector actually rises into the tank, while the cold water in the tank sinks into the collector. This is an automatic process throughout the day. The insulated tank keeps the water hot during night so that it is available to you in the morning. These systems do not require pumps because the water flows via gravity from the tank to the collector.