99600c1d_Collector___Solar_Water_Heater__Evacuated_Tube_Collector
[S.No] 3 [Flat Plate Collector] Heat loss in the collector & tank during the day-time is high due to convection. [Evacuated Tube Collector] 
Heat loss in the tubes during the daytime is negligible (evacuated tubes)
Comparison between Evacuated Tube Collector & Flat Plate Collector - Solar Water Heater
Evacuated Tube Collector