GMOI Series solar system’s vitreous enamel lined solar storage tank installed on the roof and directly connected to the solar collectors. In the Closed Circuit Series, sun heat is absorbed by the collector and passed to the heat transfer liquid inside the collector. As the temperature of the heat transfer liquid increases, the hot fluid rises up through the collector by the Natural Thermosiphon Principle, into the heat exchanger jacket around the water storage tank. The heat is transferred to the water, and cooling the heat transfer fluid at the same time. The cooler fluid flow down into the collectors and further hot fluid rising up into the heat exchanger jacket.