Electricity production.

As you already know, electricity does not grow in trees. It is produced artificially through some devices (of different sizes) which are called "power generators".

A power generator transforms kinetic energy (movement) into electrical energy.

The issue is how to produce enough kinetic energy in order to move big generators that produce also large amounts of electricity.

Alternators made in Budapest, Hungary, in the hydroelectric station in Iolotan (Eloten), Turkmenistan, in the river Murghab, circa 1910.

SOURCE: http://www.loc.gov/pictures/item/prk2000002476/ y http://labitacoradehobsbawm.blogspot.com.es/2010/08/rusia-hace-cien-anos-y-colores.html

Modern alternator. Coal-fired power plant in As Pontes, Galicia.

SOURCE: http://www.endesa.com