Domestic hot water refers to the heated water used for domestic purposes. Energy consumption for domestic hot water depends on different factors, namely consumption patterns, how much hot water is used and the increase in water temperature required (difference between the inlet and the outlet temperature). We can consider that, on average, the annual energy consumption for domestic hot water in developed countries is around 1000 kWh per person (1).
Domestic hot water demand is rather constant all year round. Solar thermal collectors are, therefore, particularly suited to meet this demand. In higher latitudes, where the radiation in winter is significantly lower than in summer, such systems can cover between 60 and 80% of the annual domestic hot water demand. This means that a supplementary or back-up heater is required. In low latitudes, solar thermal can cover 100% of the domestic hot water demand and no backup heater is required.