Compact Solar Water Heater relies on density of the water, cold water down, hot water up, a cosmical physics. To circulate water through the collectors and the tank. When water in the collectors is heated up, it becomes lighter and naturally rises into the tank. Meanwhile, cooler water in the tank flows down to the collectors.

In this type of installation, the tank must be together with the collectors. These systems are reliable and relatively inexpensive but be careful with the installation, because the water tank is much heavier than that you thought.