Environmental concerns with electricity generation
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Modern technology uses large amounts of electrical power. This is normally generated at power plants which convert some other kind of energy into electrical power. Each such system has advantages and disadvantages, but many of them pose environmental concerns.
The efficiency of some of these systems can be improved by cogeneration (combined heat and power) methods. Process steam can be extracted from steam turbines. Waste heat produced by thermal generating stations can be used for space heating of nearby buildings. By combining electric power production and heating, less fuel is consumed, thereby reducing the environmental effects compared with separate heat and power systems.
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[edit] Fossil fuels
Main article: Fossil fuels
Most electricity today is generated by burning fossil fuels. This produces high temperatures, which drive some sort of heat engine, often a steam turbine.
Such systems allow electricity to be generated where it is needed, since fossil fuels can readily be transported. They also take advantage of a large infrastructure designed to support consumer automobiles. The world's supply of fossil fuels is large, but finite. Exhaustion of low-cost fossil fuels will have significant consequences for energy sources as well as for the manufacture of plastics and many other things. Various estimates have been calculated for exactly when it will be exhausted, but new sources of fossil fuels keep being discovered.
More serious are concerns about the emissions that result from fossil fuel burning. Fossil fuels constitute a significant repository of carbon buried deep under the ground. Burning them results in the conversion of this carbon to carbon dioxide, which is then released into the atmosphere. This results in an increase in the Earth's levels of atmospheric carbon dioxide, which enhances the greenhouse effect and contributes to global warming. The linkage between increased carbon dioxide and global warming is nearly universally accepted, though fossil-fuel producers vigorously contest these findings.
Depending on the particular fossil fuel and the method of burning, other emissions may be produced as well. Ozone, sulfur dioxide, NO2 and other gases are often released, as well as particulate matter. Sulfur and nitrogen oxides contibute to smog and acid rain. In the past, plant owners addressed this problem by building very tall flue gas stacks, so that the pollutants would be diluted in the atmosphere. While this helps reduce local contamination, it does not help at all with global issues.
Fossil fuels, particularly coal, also contain dilute radioactive material, and burning them in very large quantities releases this material into the environment, leading to low but real levels of local and global radioactive contamination.
Coal also contains traces of toxic heavy elements such as mercury, arsenic and others. Mercury vaporized in a power plant's boiler may stay suspended in the atmosphere and circulate around the world. While a substantial inventory of mercury exists in the environent, as other man-made emissions of mercury become better controlled, power plant emissions become a significant fraction of the remaining emissions. Power plant emissions of mercury in the United States are thought to be about 50 tons per year in 2003, and several hundred tons per year in China. Power plant designers can fit equipment to power stations to reduce emissions.
Coal mining practices in the United States have also included strip mining and removing mountain tops. Mill tailings are left out bare and have been leached into local rivers and resulted in most or all of the rivers in coal producing areas to run red year round with sulfuric acid that kills all life in the rivers.
[edit] Hydroelectric power
Main article: Hydroelectric power
Water on the Earth goes through a constant cycle, being evaporated from the oceans, raining out on land, and running back downhill to the oceans. Hydroelectric power extracts some of the energy of this downhill flow of water. Normal hydroelectric power plants consist of a dam which creates a large reservoir; when power is needed, water is allowed to flow out of the reservoir through turbines, generating electricity.
Hydroelectric power is renewable, that is, it will not run out as long as the water continues to flow. Environmental effects stem from the operation of the reservoirs, and the associated alteration of pre-existing water flow conditions.
When a new dam is constructed, it produces a new lake (reservoir). The land that this lake covers is immersed, which renders it unavailable to animals and people and immediately swamps all the vegetation. Many animal species are threatened simply because there is not enough undamaged land for them to live on, and a large hydroelectric project may flood a large amount of this land. The lake itself may not develop into a healthy eco-system; eutrophication is a danger, and the large mass of rotting vegetation under the water does not lead to a healthy eco-system. These concerns are in a sense one time problems; once the dam is built, it can continue to produce power indefinitely while allowing a new eco-system to develop.
Hydroelectric dams may accumulate silt due to suspended solids falling out of the water in the plant reservoir. If enough silt accumulates, the water intake's to the turbines will become blocked, so hydroelectric installations must remove the silt and dispose of it somehow.
The elminiation of habitat for certain species can, rarely, result in reduction of some parasitic diseases. For example, the Nalubaale Power Station (on the Nile River in Uganda) eliminated the habitat of a blackfly that spread the parasite that causes river blindness.
Hydroelectric dams also block migration routes for fish which need to swim upriver to spawn. This has been partially addressed by building fish ladders, small streams the fish can swim up, to circumvent the dam.
Rarely is a large hydroproject close to a city or industrial factory that will use all the power produced. Usually long power transmission lines carry the electric power to its destination. Transmission line construction requires clearing a long narrow corridor of forest (or other terrain). This clearing can affect migration routes and erosion, and may permit human access to otherwise isolated areas. The effects of corona discharge and extremely low-frequency electromagnetic radiation near power lines are a source of continuing concern.
For certain projects with relatively large reservoirs (less than 100 watts of plant output per square metre of forebay), significant emissions of methane may occur as a result of anaerobic decay of submerged plant matter. This is especially true for reservoirs in tropical areas where the forebay has not been cleared before innundation. Some calculations suggest that in the extreme case the greenhouse effect due to these emissions would be of the same order as those due to a fossil-fuel plant producing the same annual energy.
The World Commission on Dams in 2004 released a report outlining a consensus on best practice for large dams, considering environmental, social and economic factors. See the report, including discussion of greenhouse gas emissions.
[edit] Tidal power
Main article: Tidal power
In regions such as the Bay of Fundy with very large tidal swings, tidal power plants can be built to extract electrical power from the tidal motion.
Tidal power is also renewable, in the sense that it will continue for as long as the Moon orbits the Earth. However, it has environmental problems similar to those of hydroelectric power. A tidal power plant usually requires a large dam, which can endanger ecosystems by restricting the motion of marine animals. Perhaps more seriously, a tidal power plant reduces or increases the tidal swing, which can severely disrupt ecosystems which depend on being periodically covered by water; resulting changes in fisheries or shellfish beds may result in adverse economic effects. Certain proposed tidal power plants in the Bay of Fundy would increase the tidal swing by an estimated 50 cm as far south as the coast of Maine (where the tidal swing is not particularly large now).
[edit] Nuclear power
Nuclear power has raised much public concern. Under normal operation, a nuclear power plant releases very little contamination of any sort to the environment. It does produce radioactive waste of several sorts. Moderate amounts of low-level waste are produced; this can be disposed of simply by placing it somewhere it won't be disturbed for a few years. However, a relatively small amount (perhaps a tonne a year from a large nuclear power plant) of high-level waste is produced, and this poses a significant disposal problem. It can be expected to be dangerous for tens or hundreds of thousands of years (Taking 10,000 years to decay to activity levels below that of the original ore), so extremely secure disposal methods must be found. Currently, most such waste is stored in temporary storage facilities which require constant care and attention. Several methods have been suggested for final disposal of the waste, including deep burial in stable geological structures, transmutation, and removal to space. Some nuclear reactors, in particular the Integral Fast Reactor, have been proposed that use a different nuclear fuel cycle that avoids producing waste containing long-lived radioactive isotopes.
Accidents at nuclear power plants pose a risk of severe environmental contamination. The Chernobyl accident, for example, released large amounts of radioactive contamination, killing many and rendering a large area of land unusable for the next few centuries. However, the power plant at Chernobyl was built with minimal concern for safety; modern nuclear power plants are much less likely to have such problems. The potential for such an accident still exists; however, many experts are still concerned about the use of nuclear power. This danger has received significant coverage in the popular press, so the public has a very strong fear of nuclear power (by contrast, the radioactive contamination due to coal burning is virtually unknown, as are most of the hazards of other methods of electrical power generation).
Nuclear power can also pose the risk of nuclear proliferation. Fission products can be reprocessed out of spent reactor fuel and diverted to a weapons program, or a reactor can be used to produce weapons materials through transmutation by direct irradiation by neutrons.
[edit] Biomass
Main article: Biomass
Electrical power can be generated by burning anything which will burn. Some electrical power is generated by burning crops which are grown specifically for the purpose. Usually this is done by fermenting plant matter to produce ethanol, which is then burned. This may also be done by allowing organic matter to decay, producing biogas, which is then burned. Also, when burned, wood is a form of biomass fuel.
Burning biomass produces many of the same emissions as burning fossil fuels. However, growing biomass captures carbon dioxide out of the air, so that the net contribution of the cycle to global atmospheric carbon dioxide levels is zero.
The process of growing biomass is subject to the same environmental concerns as any kind of agriculture. It uses a large amount of land, and fertilizers and pesticides may be necessary for cost-effective growth. Biomass that is produced as a by-product of agriculture shows some promise, but most such biomass is currently being used, for plowing back into the soil as fertilizer if nothing else.
[edit] Solar power
Main article: Solar power
Solar power extracts the energy of sunlight. This may be done directly, with photovoltaic cells, or it may be done by using fields of mirrors to concentrate sunlight on a target which then becomes extremely hot. This heat can then be dumped to the surrounding air, providing electricity. In either case, a large expanse of land receiving steady sunlight is needed. Deserts are the usual choices. Manufacture of solar cells results in environmental releases of pollutants and the emissions associated with the energy input to make and install the cells. Once a large solar collector is built, its environmental impact is not very severe. It occupies a great deal of land, denying its use to the fragile desert ecosystems, and the heated air may lead to slight changes in local weather systems. The mirrors or cells must also be kept clean, and this probably requires a certain amount of water. Where possible, solar power is generally quite environmentally friendly.
Some projects have been established to take advantage of relatively small solar cells by putting solar collectors on the roofs of individual houses. Generally, the electrical power generated is not sufficient to pay back the cost at current electricity prices, so when government subsidies are not present, this method is rarely used. It is generally more practical to use small solar collectors to heat water directly, satisfying household hot water needs.
[edit] Wind power
Main article: Wind power
Wind power extracts electricity from the flow of air over the surface of the earth. Wind power stations generally consist of large "wind farms", fields of large windmills in locations with relatively high winds. These farms are generally considered unattractive. In addition the windmills disrupt local low-level winds, and they can be very noisy. Both facts create problems for local bird populations, specifically the death of many birds. The windmills also need constant maintenance, as they have many moving parts exposed to the elements. A lot of effort is now being directed into having off-shore wind-farms that will be situated several kilometres out to sea. Supporters hope this will reduce the amenity concerns many opponents have. Many homeowners in areas with high winds and expensive electricity set up small windmills to reduce their electric bills.
A potentially more significant issue, is that of the 'spinning backup' that is required to compensate for the unpredictable and intermittent nature of wind generation in a national grid. In order to maintain a reliable supply of electricity to consumers, it is necessary to control the energy generated, increasing and decreasing it according to demand. Wind energy however, cannot be controlled as such meaning that either other power stations (Preferably those with short 'spin-up' times such as gas fired power stations) must be left on stand-by to takeover supply generation when output from wind farms falls. This however may reintroduce environmental issues with conventional electricity generation methods, somewhat curtailing the effectiveness of wind power as an environmentally friendly means of producing electricity. An alternative to compensating for the lulls in wind generation, is to effectively store the energy generated during high winds and then utilise it as required. However this requires expensive grid energy storage schemes, such as pumped storage or (At a smaller scale) Battery storage, each of which introduce further environmental concerns.
[edit] Geothermal power
Main article: Geothermal power
[edit] Negawatt power
Main article: Negawatt power
Negawatt power is a way of supplying additional electrical energy to consumers without increased generation capacity at around half the cost of large scale generation. Whilst related to and utilising consumption efficiencies it differs in scale and market behaviour. This virtual generation method can supply decades of growth of supply in place of generation thus reducing environmental impacts of generation. Put simply it costs less to increase available supply by increasing consumption efficiency than by increasing plant generation capacity.
[edit] See also
- Air pollution
- Flue gas emissions from fossil fuel combustion
- Flue gas stacks
- Flue gas desulfurization
- Fossil fuel power plant
- Power stations
[edit] References
- Consumer Utility Services Information on renewable energy types
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