photovoltaic panels, courtesy of DOE/NREL


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The nation's electrical power system
Electrical power distribution

At power plants, electricity is almost always produced by three-phase synchronous generators, generating ac power at voltages that typically range from 14 kV to 24 kV. At the site of generation, transformers step up the voltage to long-distance transmission-line levels, typically in the range of 138 kV to 765 kV. Those voltages may be reduced for regional distribution using subtransmission lines that carry voltages in the range of 34.5 kV to 138 kV. Close to major load centers, transformers in distribution system substations further step down the voltages to distribution feeders, most commonly at 12.47 kV. Finally, transformers on power poles or boxes deliver ac power to residential, industrial or commercial users at 120-600 V. The complete power distribution system, from power plants to consumers is called a power grid. All ac sources on the grid are precisely synhronized to the standard frequency (60 Hz in the U.S.). In the U.S., there are three separate power grids: Western, Eastern, and Texas, connected by high-voltage dc (HVDC) lines. Understanding of the technology and economics of the nation's electrical power system is essential for the study of potentials for wider deployment of renewable sources. This part of the course includes the following topics:

  • Generation of electricity
  • Three-phase systems, generators and power grid
  • Electrical power system capacity, stability and security
Western power grid Western power grid
U.S. electricity generation by source type
Electricity demand
U.S. electricity demand growth in TWh
Energy statistics, US DOE
More than 50% of electricity generated in the U.S. in 2006 comes from coal power plants. Less than 1% of electricity is currently produced by wind or solar power systems.  
Xcel Energy's energy sources in Colorado
Location of existing power sources in Colorado, within the Xcel Energy service area. These sources include coal-fired plants (for example, the Valmont plant in east Boulder), hydro plants such as Georgetown and Shoshone, the Cabin Creek pumped hydro storage facility near Georgetown, natural gas plants such as Ft. St. Vrain, and wind farms such as Ponnequin. A solar thermal facility is planned in Alamosa.