The U.S electric grid is not actually an unified system, but rather a complex network of local and regional power authorities. It is a giant network of independently owned power plants and transmission lines.
America’s electric grid is actually comprised of three smaller grids, called interconnections, that move electricity around the country. The Eastern Interconnection, the Western Interconnection and the Texas Interconnected system.
The power comes from several sources of energy like coal, oil and natural gas.
In the next picture we can see the approximately 5.000 power-producing facilities in the country that contribute energy to thew electric grid.
This one represent the solar power capacity of the U.S and the lines that would carry the solar energy into the electric system.
The next picture represents the wind power.
The green lines represent the wind power transmission lines in 2030; while the orange ones represents the new wind power transmission lines projected after 2030.
How Energy Grid works:
The electric power is generated at power plants and then it’s moved by transmission lines to substations. A local distribution system of smaller, lower-voltage transmission lines moves power from substations to he customer.
Only as something curious, I could mention that was Thomas Edison who created the first commercial power grid, known as The Pearl Street Station, in lower Manhattan in 1882.
Sources:
http://www.npr.org/templates/story/story.php?storyId=110997398
http://energy.gov/articles/top-9-things-you-didnt-know-about-americas-power-grid
http://www.science.smith.edu/~jcardell/Courses/EGR220/ElecPwr_HSW.html