Renewable heat
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Providing hot water

A typical water heating system is illustrated which shows the solar collector, the hot water storage tank and the associated pipe work. The principal components comprise -

  • solar water heater panel
  • dual coil hot water cylinder
  • water pump
  • temperature controller to ensure that the hot water is available at the appropriate temperature.

The fluid flowing through the solar collector is heated and then passes into the storage tank through a coil which exchanges heat to the incoming cold water. The cooled water then flows back into the solar collector to be reheated. This is an indirect system that allows the working fluid to contain anti-freeze to prevent freezing during very cold weather. In southern Europe where freezing is unlikely to occur, the heated water can be used directly.


To provide a continuous supply of hot water a secondary or auxiliary heating system is required when there is insufficient sunlight during the winter months.

Generally, the plumbing from a solar heater connects to the existing water heater, which stays inactive as long as the water coming in is hot or hotter than the temperature setting on the indoor water heater. When it falls below this temperature, the auxiliary water heater can further heat the water. High-temperature solar water heaters can provide energy-efficient hot water and hot water heat for large commercial and industrial facilities.


During summer there is generally sufficient radiation to provide almost all the hot water demand, whilst during the winter the proportion produced by solar radiation is much less. Overall about 50-60% of the annual hot water demand in the UK can be met.

A typical four-person household uses about 3,000 kWh of energy to provide hot water. This totals about 20% of the annual household use. Because of the diurnal and seasonal variation in sunlight, solar water heaters can generally supply about half of the domestic hot water needs in middle Europe, rather less in northern Europe and about two thirds in southern Europe.

KITH # Activity Age range
6.2 Solar water potential
 9 – 13  



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