Electricity in the U.S.

Electricity in the U.S. Basics

from http://www.eia.doe.gov/kids/energyexplained/sources/electricity.html

Most of the electricity in the United States is produced using steam turbines.

A turbine converts the kinetic energy of a moving fluid (liquid or gas) to mechanical energy. In a steam turbine, steam is forced against a series of blades mounted on a shaft, thus rotating the shaft connected to the generator. The generator, in turn, converts its mechanical energy to electrical energy based on the relationship between magnetism and electricity.

In steam turbines powered by fossil fuels, such as coal, petroleum (oil), and natural gas, the fuel is burned in a furnace to heat water in a boiler to produce steam.

Fossil Fuels Generate Most U.S. Power

Coal is the most common fuel for generating electricity in the United States. In 2007, nearly half (49%) of the Country's 4.1 trillion kilowatthours of electricity used coal as its source of energy.

Natural gas, in addition to being burned to heat water for steam, can also be burned to produce hot combustion gases that pass directly through a turbine, spinning the turbine's blades to generate electricity. Gas turbines are commonly used when electricity utility usage is in high demand. In 2007, about 22% of the Nation's electricity was fueled by natural gas.

Petroleum can also be used to make steam to turn a turbine. Residual fuel oil, a product refined from crude oil, is often the petroleum product used in electric plants that use petroleum to make steam. Petroleum was used to generate about 2% of all electricity in the United States in 2007.

Nuclear Power Provides About One-Fifth of U.S. Electricity

Nuclear power is a method in which steam is produced by heating water through a process called nuclear fission. In a nuclear power plant, a reactor contains a core of nuclear fuel, primarily uranium. When atoms of uranium fuel are hit by neutrons, they fission (split) releasing heat and more neutrons. Under controlled conditions, these other neutrons can strike more uranium atoms, splitting more atoms, and so on. Thereby, continuous fission can take place, forming a chain reaction releasing heat. The heat is used to turn water into steam, that, in turn, spins a turbine that generates electricity. Nuclear power was used to generate about 20% of all the Country's electricity in 2007.

Renewable Energy Sources Make Up the Rest

Hydropower, the source for almost 6% of U.S. electricity generation in 2007, is a process in which flowing water is used to spin a turbine connected to a generator. There are two basic types of hydroelectric systems that produce electricity. In the first system, flowing water accumulates in reservoirs created by dams. The water falls through a pipe called a penstock and applies pressure against the turbine blades to drive the generator to produce electricity.

In the second system, called run-of-river, water is diverted from a river using a relatively low dam or weir into penstocks and turbines. The dam does not store a large volume of water in a reservoir. Run-of-river power plants are more dependent on river flows than hydro plants with reservoirs for storing water to produce electricity when natural river flows are low.

Biomass is material derived from plants or animals (i.e. biogenic) and includes lumber and paper mill wastes; food scraps, grass, leaves, paper, and wood in municipal solid waste (garbage); and forestry and agricultural residues such as wood chips, corn cobs, and wheat straw. These materials can be burned directly in steam-electric power plants, or converted to gas that can be burned in steam generators, gas turbines, or internal combustion engine-generators. Biomass accounts for about 1% of the electricity generated in the United States.

Wind power is produced by converting wind energy into electricity. Electricity generation from wind has increased significantly in the United States since 1970, but wind power remains a small fraction of U.S. electricity.

Geothermal power comes from heat energy buried beneath the surface of the earth. In some areas of the United States, enough heat rises close to the surface of the earth to heat underground water into steam, which can be tapped for use at steam-turbine plants. This energy source generated less than 1% of the electricity in the Country in 2007.

Solar power is derived from energy from the sun.  There are two main types of technologies for converting solar energy to electricity: photovoltaic (PV) and solar-thermal electric. PV conversion produces electricity directly from sunlight in a photovoltaic (solar) cell. Solar-thermal electric generators concentrate solar energy to heat a fluid and produce steam to drive turbines. In 2007, less than 1% of the Nation's electricity was from solar power.

How Electricity Gets to Your Home

from Energy in Brief:

Electricity Is Delivered to Consumers Through a Complex Network

Electric power is generated at power plants and then moved to substations by transmission lines — large, high-voltage power lines. In the United States, the network of nearly 160,000 miles of high voltage transmission lines is known as the "grid."

A local distribution system of smaller, lower-voltage distribution lines moves power from substations and transformers to customers.

from: http://www.eia.doe.gov/bookshelf/brochures/rep/index.html

Electricity Comes from Various Sources and Kinds of Providers

The utility, distribution company, or retail service provider selling you power may be a not-for-profit municipal entity, an electric co-operative owned by its members, a private, for-profit company owned by stockholders (often called an investor-owned utility), or a power marketer. Some Federally-owned authorities — including the Bonneville Power Administration and the Tennessee Valley Authority, among others — also buy, sell, and distribute power.

The origin of the electricity you consume may vary. Utilities may generate all the electricity they sell using just the power plants they own. Utilities may also purchase some of their supply on the wholesale market from other utilities, power marketers, independent power producers, or from a market based on membership in a regional transmission reliability organization.

How the Grid Is Organized

Most of the existing grid was built during a highly structured, highly regulated era designed to ensure that everyone in the United States had reasonable access to electricity service. Utility customers, through fees authorized and regulated by State regulatory commissions, generally paid for developing and maintaining the grid.

Many local grids are interconnected for reliability and commercial purposes, forming larger, more dependable networks to maximize coordination and planning. These networks extend throughout many States.

The North American Electric Reliability Corporation (NERC) was established to ensure that the grid in the United States was reliable, adequate, and secure. Some NERC members have formed regional organizations with similar missions.

These organizations are referred to as Independent System Operators (ISOs) and Regional Transmission Organizations (RTOs). They are part of a national standard design advocated by the Federal Energy Regulatory Commission (FERC). Some have members who connect to lines in Canada or Mexico. Most, depending on the location and the utility, are indirectly connected to dozens and often hundreds of power plants. Some power consumed in the United States is imported from Canada and Mexico.

Electricity & the Environment

Although electricity is a clean and relatively safe form of energy to use, there are environmental impacts associated with the production and transmission of electricity. Nearly all types of electric power plants have some impacts or effects on the environment, some more than others.

The United States has laws to reduce these impacts. Perhaps the most important such law is the Clean Air Act, which established regulations for the control of air emissions from most power plants. The Environmental Protection Agency (EPA) administers the Act and sets emissions standards for power plants through various programs, such as the Acid Rain Program. The Act has resulted in a substantial reduction of emissions of some of the major types of air pollutants in the United States.

The Impact of Power Plants on the Landscape

All power generators or plants have a physical footprint (the area where they are placed or located). Some can be located inside, on, or next to an existing building, so the impact of their footprint is very small. Most large power plants require clearing land to locate the power plant and any necessary fuel storage areas (in the case of hydro-power dams, a reservoir forms behind the dam). Some plants may also require the construction of access roads, rail, pipelines, transmission lines, and access to cooling water supplies or reservoirs.

Besides the physical footprint, many power plants are large physical structures that have impacts on the visual landscape. Some people may not like this especially where the landscape is relatively natural or pristine.

In general, the larger the area disturbed, the greater the real and potential impacts on the landscape.

Fossil Fuel-, Biomass-, and Waste-Burning Power Plants

In the United States, fossil fuels (mainly coal, oil, and natural gas), materials that come from plants (biomass), and municipal and industrial wastes are used to generate most of the electricity we use; about 72% in 2007. Emissions that result from the combustion of these fuels include:

• Carbon dioxide (CO2)
• Carbon monoxide (CO)
• Sulfur dioxide (SO2)
• Nitrogen oxides (NOX)
• Particulate matter (PM)
• Heavy metals such as mercury

Nearly all combustion byproducts have negative impacts on the environment and human health:

• Carbon dioxide is a greenhouse gas and a source of global warming.1
• SO2 causes acid rain, which is harmful to plants and to animals that live in water, and it worsens or causes respiratory illnesses and heart diseases, particularly in children and the elderly.
• NOX contributes to ground level ozone, which irritates and damages the lungs.
• PM results in hazy conditions in cites and scenic areas, and, along with ozone, contributes to asthma and chronic bronchitis, especially in children and the elderly. Very small, or “fine PM” is also thought to cause emphysema and lung cancer.
• Heavy metals such as mercury can be hazardous to human and animal health.

Power Plants Use Air Emission Controls

Power plants are required to meet standards that limit the amounts of some of the substances that they release into the air. There are different ways that power plants meet these standards:

• Coal-fired plants can use coal that is low in sulfur content. Coal can also be pre-treated and processed to reduce the types and amounts of undesirable compounds in combustion gases.
• Particulate matter emissions are controlled with devices that clean the combustion gases that exit the power plant:
  • “Bag-houses” use large filters
  • Electrostatic precipitators use charged plates
  • Wet scrubbers use a liquid solution
• SO2 emissions are controlled by wet and dry scrubbers, which involves mixing lime in the fuel (coal) or by spraying a lime solution into the combustion gases. Fluidized bed combustion can also be used to control SO2.
• NOX emissions can be controlled by several different techniques and technologies, such as low NOX burners during the combustion phase or selective catalytic and non-catalytic converters during the post combustion phase.

Some Plants Also Produce Liquid and Solid Wastes

The coarse solid mineral residue that results from the burning of coal is called bottom ash. The individual particles are much larger than fly ash particles and fall down through the air flow to the bottom of the boiler. Particulates collected in air emission control devices (“fly ash”) are usually mixed with the bottom ash. The resulting “sludge” from coal-fired power plants may be stored in retention ponds, sent to landfills, or sold for use in making concrete blocks or asphalt.

Most Power Plants Produce Greenhouse Gasses

Greenhouse gases contribute to the “greenhouse” effect. Scientists know with virtual certainty that increasing greenhouse gas concentrations tend to warm the planet.2

Power plants that burn fossil fuels and materials made from fossil fuels and some geothermal power plants are the sources of about 40% of total U.S. carbon dioxide (CO2) emissions.

Nuclear Power Plants Produce Different Kinds of Waste

Nuclear power plants are not a source of greenhouse gases or other emissions, but they do produce two kinds of radioactive waste:

• Low-level radioactive waste — This includes items that have become contaminated with radioactive material, such as clothing, wiping rags, mops, filters, reactor water treatment residues, and equipment and tools. Low-level waste is stored at nuclear power plants until the radioactivity in the waste decays to a level where it is allowed to be disposed of as ordinary trash or it is sent to a low-level waste disposal site.
• Spent (used) nuclear fuel — The spent fuel assemblies are highly radioactive and must initially be stored in specially designed pools resembling large swimming pools (water cools the fuel and acts as a radiation shield) or in specially designed dry storage containers. An increasing number of reactor operators now store their older spent fuel in dry storage facilities using special outdoor concrete or steel containers with air cooling.

Electric Power Lines Also Have a Footprint

Power transmission and distribution lines carry electricity from power plants to customers. Most transmission lines are strung above ground on large towers. The towers and lines impact the visual landscape, especially when they pass through pristine natural areas. Trees near the wires may be disturbed and have to be managed to keep them from touching the wires and these activities can affect native plant populations and wildlife. Power lines can be placed under the ground, but this is more expensive and may result in a greater disturbance of the landscape than overhead lines.

1. U.S. Environmental Protection Agency, Climate Change State of Knowledge.
2. Intergovernmental Panel on Climate Change.