Solar Thermal Energy

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Solar thermal: definition and technological and economic considerations.

Solar thermal recovers heat from the sun with a fluid that circulates in the panels. In mainland France, the solar thermal represents over 55 000m² panels.

Principle of operation

A solar heat panel is designed to transmit the heat generated by the sun to a secondary water circuit. The sun's rays pass through the window, within an absorbent plate which is intended to receive the infrared rays. Behind the hot plate passes a water circuit that recovers the heat.

Subsequently this circuit supplies a secondary circuit that can power a home or domestic water heating.

The flow of water little be by simple physical phenomenon, the hot water is less dense than cold water. This is why in the diagram the hot water is always above the cold water.

Advantages :

  • high efficiency (up to 80%) can be recovered up to 1200 W / m² calories in France (the best solar panels and the best sunshine).
  • allows to heat water "for free" after return on investment, which can be interesting for communities who want to control their expenses such as energy-intensive pools.
  • inexhaustible source of energy but care facilities wear them ... especially if the installation was done hastily,
  • huge development potential.


  • generally limited to heat the hot water unless you have a low temperature floor heating
  • solar thermal energy remains an expensive energy compared to heating with fossil fuels due to relatively heavy investment (of € 500 1500 to the m2 installed)
  • return on investment long enough (a return to 10 15 years is not unusual)
  • lifetime of the panels is generally limited to 20 years,
  • Some panels are very sensitive and can be damaged by certain weather conditions (hail, frost ...)
  • billing equipment in many cases,
  • essort "controlled" by subsidies and various aid (double-edged).

Principle of a thermal solar panel for hot water.

Conclusions: high potential but an energy that is still expensive.

Solar is one of the oldest "renewable" energies. Prehistoric men already used it to, for example, dry their fish.

Today she is back on center stage with the depletion of fossil fuels and global warming and its potential for development is very important because very few people use.

Finally, to conclude, we would still add a word about state subsidies.

If it possible to democratize solar conversely they also enable billing facilities (subsidies are provided only on the most expensive facilities) ...

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