POWERING THE U.S.

Electrical energy is arguably one of the least appreciated but most important commodities of our modern society. In the U.S., electricity is available close to 100% of the time and at virtually every household and business.  Running our economy requires huge amounts of electricity every second of every day. It is embedded in nearly all forms of our lifestyle, from retail services and manufacturing products to food and entertainment.  Yet most people have very little contact with how it is produced or how much we use.

Electrical energy is produced through the conversion of the energy found in various fuels or resources on earth. The type of conversion depends on the energy source, or “fuel”.  The table below is a summary of the nine primary energy sources used today to produce electricity:

Energy Source Conversion Process U.S. percentage New York percentage New England percentage   Coal Coal is mined from the ground and transported to large power plants. The coal is burned in a boiler to heat water to high pressure steam. The steam is sent through a turbine which spins a generator to produce electricity. 49.8% 14.5% 14.4%   Nuclear Uranium is mined from the ground and transported to large power plants.  The uranium is enriched and undergoes controlled nuclear fission to produce heat which turns water to high pressure steam. The steam is sent through a turbine which spins a generator to produce electricity. 19.9% 25.4% 27.3%   Natural Gas Natural gas is extracted from the ground and delivered via pipelines or (shipped in liquified form) to large and small power plants. The gas is burned directly in a gas turbine which spins a generator to produce electricity. In some cases, excess heat exhausting from the gas turbine is used to heat water to steam to drive a steam turbine, producing more electricity. Natural gas can also be burned directly in a boiler similar to a coal power plant. 17.9% 16.6% 36.8%   Oil Oil is extracted from the ground and transported to power plants.  The oil is burned in a boiler (or directly in a gas turbine) to create electricity similar to natural gas.  Reciprocating engines (similar to automobile engines) are also used to produce electricity in smaller amounts. 3.0% 13.0% 9.4%   Hydro- electric Flowing water is sent through turbines to spin generators.  Dams are typically used to contain and control the water for storage and to create a large enough elevation drop to provide sufficient water pressure to spin the turbines. 6.6% 17.2% 5.1%   Biomass Biomass consists of waste wood, municipal solid wastes, landfill methane, agricultural wastes and other organic waste materials. Typically these are burned in a boiler to produce steam which is sent through a turbine to spin an electric generator.  Other methods include direct use of the gas (or indirect via anaerobic digestion) in a reciprocating engine or very small gas engine. 1.5% 1.5% 6.6%   Geothermal Hot water or steam from underground hydrothermal sources is extracted to run turbines which spin an electric generator. 0.4% -- --   Wind Wind moves aerodynamically designed blades about a central hub.  The hub turns a shaft which spins an electric generator. 0.4% ~0.1% <0.1%   Solar Typically, solar electricity is produced from photovoltaic cells, where photon energy from sunlight creates a flow of electrons in a doped silicon material.  Many cells are manufactured together to create a solar array, and the electricity (in direct current) is converted to conventional alternating current by inverters.  On a larger scale, electricity can be created by means of solar thermal, where fluids are heated to produce high temperatures to run turbines or heat engines. <0.1% <0.1% <0.1%   Other Emerging technologies and uses of conventional fuels are being developed. Tidal power, fuel cells, coal and biomass  gasification --as examples-- are all conversion processes which make use of conventional fuels and resources listed above.

    sources: 2004 DOE Energy Information Administration; 2004 NYSERDA “Patterns and Trends - New York State Energy Profiles: 1990-2004” 
     (note: may not add to 100% due to imports and exports)

Power plants operate differently depending on their fuel source and conversion process.  Coal and nuclear plants, for example, benefit from having fuel stored on site, but can not increase or decrease their output at a fast rate to respond to large changes in customer demand. Natural gas turbines can operate at greater variability, but are also subject to more volatile natural gas prices and may not operate as frequently when prices are high. Renewable fuels (biomass, geothermal, hydroelectric, wind, and solar) may have low operating costs but typically are subject to the variability of the natural resource it relies upon.

Most power plants are connected to the power transmission grid -- a network of high voltage cables carefully controlled and monitored to insure that consumers’ energy needs are reliably met.  Some businesses and homeowners generate their own power as well. 

Each conversion process has different operating efficiencies, different byproducts, and different impacts to the environment. The right combination of these diverse power sources can be effectively managed to provide high reliability, price diversity, and reduced environmental impacts.

Several good web sites to learn more:

www.eia.doe.gov/basics/electricity_basics.html U.S. Department of Energy’s Energy Information Administration. Lots of statistics throughout their web site. www.nrel.gov/ U.S. Department of Energy’s National Renewable Energy Laboratory.  Good information on renewable energy.

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