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Solar thermal

Solar thermal energy is a technology for collecting solar energy for thermal energy (heat). Solar thermal collectors are defined by the as low-, medium-, or high-temperature collectors. Low temperature collectors are flat plates generally used to heat swimming pools. Medium-temperature collectors are also usually flat plates or evacuated tubes collectors based but are used for creating hot water for residential and commercial use. High temperature collectors concentrate sunlight using mirrors or lenses and are generally used for electric power production or heat storage.

Two most available types of collectors are popular in the market: flat plates or evacuated tubes collectors.

Solar thermal technologies utilise the heat from the sun for water heating demand of a building. In the Lithuania on a horizontal surface approximately 1000 W/m2 of free energy is available.

In general, solar thermal systems consist of the following components:
  • Solar collector
  • Solar tubes loop
  • Working fluid
  • Storage tank
  • Heat exchanger
  • Pump
  • Control system
The solar collector (either flat plate or evacuated tube) absorbs heat from the sun. The heat is transferred to a working fluid (water or refrigerant), which is pumped through the solar collector during periods of solar radiation. The heat absorbed by the working fluid is transferred to the water in a hot water tank, either directly or via a heat exchanger. Finally, an electronic control system is used to determine when to pump the working fluid to the collector array. Solar heat energy delivered to the storage (hot water tank) medium increases the temperature of the water stored within. This reduces energy input from the conventional system to heat the water to the necessary temperature, which in turn reduces the energy bills for the user.
Solar thermal systems are generally designed to meet 90-100% of the water heating demand in the period of highest resource (summer) and typically 50-60% of the water heating demand averaged over the year for household.


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