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2.6 Environmental Impact of Electricity Generation and Transmission

All energy conversion methods used to produce electricity have some environmental impact. The impact may have an active effect like the emission of airborne pollutants, or may have a passive effect like aesthetics or habitat modification. Even methods considered environmentally friendly, like wind, solar, and hydro, have some impact on the environment. Not only does the final production of electricity have an environmental impact. The transmission of electricity with concerns over electromagnetic fields, aesthetics, and land use, also impacts the environment.

The whole cycle of electricity generation must be considered when looking at the environmental impact. This includes the production and transportation of fuel for the conversion process. This is especially true of fossil fuel and nuclear power plants, which use large quantities of fuel taken from the earth. Energy system environmental impact consists of fuel recovery and production, fuel transportation, electicity transmission, and spent fuel emissions.

2.6.1 Environmental Effects of Raw Fuel Production

Coal Production

Coal is almost exclusively produced for electrical generation. Coal production is often viewed as only a local environmental problem. Coal mining, particularly surface mining, has both long-term and short-term effects on land, including dust, noise, and water drainage/runoff. Preparation of coal produces both solid and liquid waste of which must be treated and disposed. Transportation of coal produces dust while coal storage produces dust to control and also results in water runoff problems.

Oil Production

The fuel oil burned in power plants is a byproduct of the petroleum industry, so electricity production is partially responsible for environmental issues associated with oil and hydrocarbon burning. This fuel burning produces many "greenhouse" gases. Other environmental impacts associated with oil production include blowouts, spills, brine disposal, and the production of hydrogen sulfide. Transportation of oil involves spill and leak hazards. Oil refining includes environmental effects such as explosions, fires, air emissions, noise, odor, and water runoff.

Natural Gas Production

During the natural gas production, possible environmental effects include blowouts, leaks, hydrocarbon emissions, and trace metal emissions. The treatment of natural gas involves air emissions and the disposal of liquid residuals, while transportation and storage effects include spills and explosions.

Uranium Production

Uranium mining involves concerns such as radioactive dust releases, mine water seepage, protection of workers from radioactivity, and the disposal of a large quantity of mine waste containing a low level of radioactivity. Uranium treatment must dispose of mill tailings containing toxic metals and chemical wastes used in the treatment process, as well as radiological waste. The treatment of raw uranium also must deal with radioactive dust releases. The enrichment of uranium ore must account for liquid and gaseous effluent releases, and must recycle fission products. Transportation involves the hazard of the accidental release of radioactive particles.

2.6.2 Environmental Effects of Electricity Production

Fossil fuel power plants generally have the most widespread effect on the environment, as the combustion process produces airborne pollutants that spread over a wide area. Nuclear power plants have the most potentially dangerous effect. An operating accident at a nuclear station could allow a large release of radioactive particles to occur. Solar, hydro, and wind power plants generally have smaller effects on the environment.

Fossil Fuel Power Plants

Fossil fuel power plants produce environmental problems including land and water use, air emissions, thermal releases, climatic and visual impacts from cooling towers, solid waste disposal, ash disposal (for coal), and noise. Due to the need for large amounts of steam, plants can have a great effect on water use. For example, a typical 500 MW coal fired power plant uses 25 x 109 l/GW-year of water, which must be taken from a water source, and then cooled to return to the water source with as little environmental effect as possible. The biggest effect fossil fuel plants have overall is the emission of air pollutants, particularly SOX, NOX , CO, CO2 , and hydrocarbons. Carbon monoxide, CO, carbon dioxide, CO2, and the hydrocarbons are the "greenhouse gases," believed to be responsible for global warming. SOX and NOX produce acid when released into the atmosphere, leading to the production of acid rain. Table 2.6 list approximate amounts of airborne pollutants produced. Generally, air emissions are controlled by the use of scrubbers and precipitators located at the plant.

Table 2.6

Power Plant Emissions (g/kWh)

Plant Type

CO

NOX

SO2

CO2

Coal

0.11

3.54

9.26

1090

Oil

0.19

2.02

5.08

781

Gas

0.20

2.32

0.004

490

Nuclear Power Plants

Nuclear power plants have one environmental issue no other form of electrical power plant does. An accident at a nuclear power plant may release large amounts of radioactive particles, possibly resulting in a direct loss of life, and rendering a large land area immediately around the plant unlivable. The largest regular environmental impact is the disposal of the high level nuclear waste contained in spent fuel rods, as this waste must be stored safely for thousands of years. There is no site in the United States currently accepting high level nuclear waste, so utilities are generally storing the waste in above ground casks at plant sites. A long term issue is the decommissioning of nuclear power plants. Decommissioning is shutting down a nuclear plant after its operational life is over. At this point the entire reactor vessel becomes a high level radioactive waste that must be disposed. The current methods of decommissioning a plant are to completely remove and dispose of all radioactive components, to entomb the reactor in concrete, or simply to shut the plant down and restrict access until the radioactivity dies out.

Solar

The production of electricity from solar energy sources generally has a small effect on the environment. There are no residuals produced in the energy conversion process. The only exception is solar thermal processes, which have an operating fluid that must occasionally be discharged. There are some environmental concerns, however. Bulk solar plants generally require a large land area, and they produce a great deal of heat. An unknown quantity in solar energy is the disposal of photovoltaic cells. The most promising solar cells use gallium arsenide, a toxic substance.

Hydro

The use of hydropower to produce electricity can have both positive and negative effects on the environment. At some sites, a dam may help with flood control, flow regulation, or the reservoir may provide recreational opportunities. At other sites, the dam may have adverse effects on the hydrological cycle, water quality of the stream, stream ecology, fish migration, and cause the destruction of landscapes and ecosystems. Building new high-head dams requires the displacement and compensation of populations. Low-head dams generally have a benign effect on the environment. Dam failures can lead to catastrophic floods.

Wind

Wind generators biggest environmental effects come from visual pollution, noise, and TV interference. This is particularly true of wind farms, where 50 or more wind turbines may be mounted at the same site. Wind farms situated on a migratory path may pose major hazards to birds. There is also a safety hazard in case of blade breakage.

2.6.3 Environmental Effects Of Electricity Transmission

Transmission of bulk electricity from the generating station to the load uses wires suspended on large towers, known as transmission lines. Traditionally these lines have been viewed only as an aesthetic nuisance that could cause communications interference and be a hazard to low flying aircraft. Today, there are other issues considered about the effect of transmission lines on the environment. Greater concern is placed on the effect of the lines on the natural habitat. The major new issue is the effect of electromagnetic fields (EMFs) on human health.

More than 1000 studies have been performed since 1979 to assess the relationship between low frequency magnetic fields and human health. Most of the research has focused on the relationship between cancer rates and fields produced in the 50-60 Hertz range used for electricity transmission. The studies generally focus on children with residential exposure to high voltage transmission lines, or workers with high degrees of occupational exposures to EMFs. Most of the studies have failed to establish a statistically significant relationship between cancer and EMFs. One difficulty in the studies is estimating the amount of EMF exposure a person receives.

Magnetic fields are produced when current flows through a conductor. The strength of the magnetic field decreases quadratically with distance from the conductor. While the strength of a magnetic field directly underneath a transmission line is in the range of 300 to 600 milliGauss (mG), the field strength is only 10 to 100 mG 200 feet away. This is in comparison to the earth's natural magnetic field of approximately 450 mG. Home appliances like hair dryers, microwaves, and televisions produce magnetic fields, ranging in strength from 1 to 50 mG. Obviously, due to the large number of different sources of EMFs, estimating a person's daily exposure becomes extremely complex. The studies generally used a broad estimate of EMF exposure.

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