Solar water heaters harness the sun’s energy to heat water. They can save energy by 20%. The time and extent of such heating depends upon the climate too.
"Installation of solar water heaters is mandatory for all buildings where hot water is required in the city municipalities and corporations, according to a Government Order. Several residents have installed solar water heaters for domestic use"
Source: The Hindu
"Infosys and Wipro are planning to be carbon neutral companies by 2017"
Evacuated tubes contain practically no water and so they can resist freezing conditions. The curved shape of the tubes allows thermal absorption from a greater range of sun angles, and, therefore, for a greater portion of the day. Tubes in ETC type permit high heat retention and so much of the heat collected during the day can be retained during overcast days and through the night. These tubes can be individually removed and replaced without having to decommission the entire system.
Flat-plate collectors typically consist of copper tubes fitted to flat absorber plates. The most common configuration is a series of parallel tubes connected at each end by two pipes - the inlet and outlet manifolds. The flat plate assembly is contained within an insulated box, and covered with tempered glass.