... tank 3) Thick insulation layer,best density solar hot water energy Material Accessories: MG rod, electrical heating, assistant tankLogo: ... 1800mmWater tank capacity150L-300LHeat preservation72 hoursDay efficiencymore than 45%Heat collectorall glass vacuum tubeQuantity of vacuum tubes16,18,24, ... coating inside of tube can absorb more than 92% heat energy from sunshine. The cold water in water tank flows ...