Electric Power

Power Efficiency Guide

Ultimate Guide to Power Efficiency

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Power is defined as the energy that is consumed or converted in a certain amount of time. In a simple electrical circuit, the power is found by multiplying the voltage and current. An electric current is the movement of charged particles measured in amperes and the voltage of the force driving them. Current that flows in one direction only, such as the current in a battery-powered flashlight, is called direct current. Current that flows back and forth, reversing direction again and again, such as household current, is called alternating current. Household electricity bills are computed on the basis of how many thousand-watt hours (kWh) of energy are consumed over a certain period of time. Today's home consumes, on average, between twelve hundred and two thousand kWh per month.

Most of the world's electric power is generated in steam plants. In a steam turbine generator, fossil fuel, such as coal, oil, natural or synthetic gas

Two lines of horizontal axis wind turbines create energy on a wind farm in Altamont Pass, California. (Kevin Schafer/Corbis-Bettmann. Reproduced by permission.)

are the most common fuels used. Coal-based generation produces about 45 percent of all electricity generated in the United States, and natural or synthetic gas about 35 percent. The remaining, approximately 20 percent of generated electricity derives mostly from nuclear power plants, but includes wind, solar, biomass, diesel, geothermal, hydro, and other sources.

In a power plant, electricity is generated when a loop of conducting wire rotates in a magnetic field. Burning coal or gas produces hot steam that is forced through a turbine, causing it to spin. The spinning motion drives the generating coils within a magnetic field to produce electricity. Modern electricity-generating plants usually have a series of turbines to more effectively utilize the steam heat. The hot water returning to the boiler is used to preheat the fuel, allowing more efficient firing. See the illustration for a diagram of how electricity is generated by burning coal.

An electric power system consists of six main components: the electric power generating plant; a set of transformers at the plant to raise the generated electricity to the high voltages used on the transmission lines; the transmission lines; the substations at which the power is stepped down to the voltage that can be distributed to consumers; the distribution lines; and the transformers that lower the distributed voltage to the level needed by residential, industrial, and commercial users.

New gas turbine generators (analogous to big jet engines) are now being built that burn natural or synthetic gas as it is injected directly into the turbine system. This reduces heat loss and increases the efficiency of the fossil fuel.

Two lines of horizontal axis wind turbines create energy on a wind farm in Altamont Pass, California. (Kevin Schafer/Corbis-Bettmann. Reproduced by permission.)

HOW ELECTRICITY IS MADE

Cooling Tower

Secondary Water Treatment

Primary Water Treatment

Water from Reservoir, Lake

Cooling Tower

Secondary Water Treatment

Primary Water Treatment

Water from Reservoir, Lake

Among the most modern systems are coal gasification or biomass gasification, which produce synthetic gases (syngas) by refining coal or biomass in a high-heat, pressurized system (gassifiers). Syngas is a more efficient fuel and contains less pollutant than either biomass or coal. Nitrogen and sulfur products are captured in the conversion process and become industrial and agricultural chemicals. At present, these systems remain expensive to build and much of the technology is still being improved. However, gasification systems are becoming more competitive with coal- or gas-fired steam plants as the costs of pollution abatement continue to rise.

As energy is converted to electricity, it flows to a transmission station where transformers change a large current and low voltage into a small current and high voltage. The electricity flows over high voltage transmission lines to a series of transmission stations where the voltage is stepped down by transformers to levels appropriate for distribution to customers.

Coal has the lowest heat values (British thermal units (BTUs) or BTU per ton) of any of the common fuel sources in the world today. When it is burned to generate steam, the major pollutants are sulfur, nitrogen, very fine ash, and mercury. The amounts of sulfur and nitrogen emitted when coal is burned depend on the kind of coal and where that coal is mined. In the United States, high-sulfur coal is mined in the Appalachian region, New York to Kentucky and the region south of the Great Lakes, Illinois, Iowa, and Kansas. These are the bituminous coal types, with high BTU per ton. Low-sulfur coal is mined in the Midwest and the intermountain regions (Wyoming, Colorado, Utah, and the Dakotas). This coal is mostly bituminous and subbitu-minous. Subbituminous coal has a lower BTU per ton rating. The nitrogen content of coal varies significantly and does not have the unique geographic distribution of sulfur. Finally, in the Dakotas, there is lignite, which is literally carbon-based earth. It has a very low BTU per ton rating, and is one of the most abundant coal types in the northern Great Plains.

biomass all of the living material in a given area; often refers to vegetation

British thermal unit (BTU) unit of heat energy equal to the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit at sea level bituminous soft coal, versus the harder anthracite coal

Lumens per watt 0

75 100 125 150 175

Efficacy (lumens per watt)

Lumens per watt 0

75 100 125 150 175

Efficacy (lumens per watt)

The energy performance of lamps is expressed as efficacy which is a measure of light output, in lumens, per watt of electrical input (lumens per watt). The efficacy of a regular incandescent light bulb is only a fraction of the efficacy of a flourescent bulb.

Pollution from electric power generation depends on the type and source of fuel. The emissions, when not captured, produce oxides of nitrogen, commonly referred to as NOx, and sulfate aerosols from sulfur and oxygen, commonly referred to as SOx. Both pollutants are chemically unstable when emitted into the atmosphere and combine with oxygen and moisture to form the SOx and NOx particulates that are recognized as the pollutants. NOx is highly reactive with other pollutants found in urban and industrial areas and, with sunlight, forms smog. SOx is often attributed as the primary source of acid deposits across the landscape, particularly in the northeastern United States, which is downwind from power plants in the Midwest.

Mercury is emitted as elemental mercury vapor. It settles only a short distance from the stacks of power plants. However, it very quickly changes to a methyl mercury form, and when it settles into water, streams, lakes, or cooling ponds, it is absorbed by plants and transferred up the food chain to fish and waterfowl eaten by humans. Although the total annual tonnage is small, science is showing that extremely small amounts of mercury can cause significant harm to humans, particularly the unborn and very young children.

Most ash from burning coal is collected at the bottom of the fire box. However, very fine ash can float out of the smokestack. The particle size that concerns present-day regulators falls in the 10 micron and 2.5 micron range. A micron is one-thousandth of a millimeter. Airborne particulate this small may be contributing to increases in childhood asthma. Electric power generation is not the only source of such particulates in urban and suburban areas. Vehicle emissions from gasoline and diesel engines are also significant contributors.

The ash residual from burning coal is often suitable for the production of road surfaces, some forms of concrete, and lightweight blocks used to reduce erosion along rivers and streams. Once considered a pollutant or waste and dumped into open pit coal mines, coal ash is now becoming a valuable commodity.

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Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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