Flat-plate collectors 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.
The solar water heater absorbs light by means of a collector placed on the roof and converts it into heat. It passes this heat to a water tank by means of a circulating pump. This exchange is triggered by the thermal regulator, but only when the collector is hotter than the water in the tank. This prevents the circulating pumps using electricity needlessly. Conversely, it also prevents overheating.
The efficiency of the collectors is at its highest at midday, in summer, when the sky is cloudless, and when the collectors face south.
When there is insufficient sunlight, the water is preheated and a back-up system takes over to bring the water to the required temperature. This system can therefore be used to produce hot water at a constant temperature throughout the year without emitting any CO2.
Solar water heaters are typically described according to the type of collector and the circulation system.