Wind and hydropower are indirect solar energy generated by the movement of air masses and water resulting from the cyclical warming of the Earth by the sun.

Wind energy is the kinetic energy of the air mass moving between areas at different pressures. Wind energy has been harnessed since ancient times, either in horizontal axis or vertical wind turbines, or to propel sailing ships.

The windmill uses are many, with, in order of increasing installed capacity:

• maritime signaling (30 W to 5 kW);

• telecommunications (60 W to 5 kW);

• battery charging in developing countries;

• pumping and desalination of water (1-5 kW);

• domestic use (several kW);

• electricity generation in wind farms of increasing power (up to approximately 200 MW) connected to the network and debiting when it is windy. More than 20,000 machines were installed in the world, with a capacity close to 100 GW, of which more than 25% in the United States and 65% in Europe.

Since 2000, the global installed capacity of wind power increased from 30 to 40% per year, reaching almost 120 GW in 2008, electricity production being estimated at 260 TWh.

The most powerful machines have a rated power of a few MW.