What is the difference between Evacuated Tube Collectors (ETC) and Flat Plate Collectors (FPC)?

The Evacuated Tube Collector consists of a number of rows of parallel transparent glass tubes connected to a tank. These glass tubes are cylindrical in shape and more efficient as they extract heat even in low sunlight. In a Flat Plate Collector, sunlight passes through the outer glass plate covering and strikes the absorber plate which heats up, converting solar energy into heat energy. Thus, the heat is transferred to the water passing through pipes attached to the absorber plate by means o convective heat transfer. Flat plate collectors are long-lasting and cheaper in the long run.