How does it form?
The historical and most common way of generating electricity is to rotate a copper coil inside magnets. Therefore, to create electricity, one must have the power to rotate the large copper coils within the magnetic field of the magnets. The most common way is with steam to drive the rotor. Waterfall from dams is also widely used, but comprises only a small percentage (and growing smaller) of the electrical generation. The power of the wind is increasingly used to turn the rotors to generate electricity, but it is still only a tiny percentage,-- AND the wind only turns the rotor core about 20% of the time.
The latest figures from the U.S. Energy Information Agency tell us that 90.3% of our electricity in 2006 was generated by turning the rotor core by steam. To get the steam to turn the rotor core, you have to boil water. Therefore, a fuel is used to heat the water to the boiling point, or beyond. For 88% of our electricity, the fuel to heat the water is either coal, natural gas, or a nuclear reaction.