... 0.31mm5,Insulation:foaming polyurethane thickness:50mm or 55mm6,Optional electric heater:220v-240v 1500w/3000w7,frame material :202 stainless steel8, ... in the top of the water tank ,and the cold water sink to bottom,then heat by solar collector.so the whole ... its valve,the tap water flow in the tank ,if the water is full,it will close the valve automatically solar collector tube for solar water heater