Flat panel collectors working principle is different from evacuated tubes collector. A glazed flat-plate solar collector consists of a shallow rectangular box with a flat black plate behind a tempered glass cover. The plate is attached to a series of parallel tubes or one serpentine tube through which water or another liquid (such as an antifreeze solution) passes. Sunlight passes through the glazing and strikes the absorber plate, which heats up, converting the sunshine into heat energy. The heat is transferred to the liquid passing through the pipes attached to the absorber plate.