99600c1d_Collector___Solar_Water_Heater__Evacuated_Tube_Collector
[S.No] 11 [Flat Plate Collector] Higher system sizing is required to get the desired result. Hence added cost. [Evacuated Tube Collector] 
In locations with average availability of solar energy over-sizing of the system glass tube collectors is not required.
Comparison between Evacuated Tube Collector & Flat Plate Collector - Solar Water Heater
Evacuated Tube Collector