A energy source indicates all the phenomena from which it is possible to withdraw energy.

The following phenomena are often indicated like energy sources:

• Wind (wind energy);
• Water combined with the Revolved (hydraulic power);
• Tide S and current sailors (tidal energy and Hydrolienne)
• Solar energy (thermal and Photovoltaic);
• Combustion (Combustible: Oil, Natural gas, Biogas, Wood,…);
• Nuclear energy coming from the Fission or the nuclear Fusion.

It is possible to go up towards a more remote source of these energy sources. For example, wind energy and the hydraulic power are a form transformed (energy Cinétique and gravitational, respectively) of the received energy of the Sun by electromagnetic Rayonnement . The Pétrole is also a form of stored solar energy, but on another scale of time (hundreds of million years). Another example, the tidal energy originates in the gravitational energy of the system Ground - the Moon. To go even further, one can say that solar energy comes from the energy of the Big Bang which allowed the formation of Hydrogène, fuel of the nuclear Fusion.

This reflection is important in the context of the discussions around the renewable energy.