5. Wind power (Where does wind get its power from?)

For thousands of years, mankind has used the power of the wind. The early Egyptians and the Phoenicians sailed the Mediterranean. Whether wind mills were also used during antiquity is still under debate.
During the 20th century, two innovations took place: The use of wind in combination with a power generator and the invention of the wind rotor.
Today, wind power is the most important amongst the renewable energies. But one problem remains: Wind is variable. But how does wind regenerate? And where does it get its power from?