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12Статья поступила в редакцию 07.03.11. Ред. рег. № 953 The article has entered in publishing office 07.03.11. Ed. reg. No. 953
УДК 504.05
ЭКОЛОГИЧЕСКИЕ ПОСЛЕДСТВИЯ ИСПОЛЬЗОВАНИЯ ЭНЕРГИИ ОКЕАНА
С.М. Говорушко
Тихоокеанский институт географии ДВО РАН 690041 Владивосток, ул. Радио, д. 7 Тел./факс: 8(4232)311653, e-mail: sgovor@tig.dvo.ru
Заключение совета рецензентов: 25.03.11 Заключение совета экспертов: 10.04.11 Принято к публикации: 15.04.11
Рассмотрено современное состояние мировой альтернативной энергетики. Дана характеристика основных видов энергии океана (приливная, волновая, осмотическая, энергия океанических течений, энергия перепада температур). Проведен анализ воздействия на окружающую среду вследствие их использования. Сделан вывод о будущем неизбежном росте значимости применения этих видов энергии в глобальном энергобалансе.
Ключевые слова: альтернативная энергетика, волновые электростанции, осмотическая энергия, приливные электростанции, энергия разницы температур, энергия течений, энергия океана, экологические последствия.
ENVIRONMENTAL CONSEQUENCES OF OCEAN ENERGY USING
S.M. Govorushko
Pacific Geographical Institute FEB RAS 7 Radio str., Vladivostok, 690041, Russia Tel./fax: 8(4232)311653, e-mail: sgovor@tig.dvo.ru
Referred: 25.03.11 Expertise: 10.04.11 Accepted: 15.04.11
The current state of the global alternative electricity industry is described. Characteristics of main types of ocean energy (tidal, wave, osmotic, energy of ocean currents, energy of temperature difference) are given. The analysis of the impact on the environment due to their use is realized. Concluded that the future growth of the significance of these kinds of electricity industry in energy balance is inevitable.
Keywords: alternative power structures, environmental consequences, energy of currents, energy of temperature differences, ocean energy, osmotic energy, tidal stations, wave farms.
ПРИЛИВНАЯ ЭНЕРГЕТИКА И ЭНЕРГЕТИКА МОРСКИХ ТЕЧЕНИИ
TIDE ENERGY AND SEA TIDE ENERGY
Current state of global alternative power engineering
The category of non-traditional or alternative power structures includes power plants that use renewable energy sources. Strictly speaking, hydraulic power is also a renewable source, but it, along with thermal and nuclear power, is generally categorized as traditional power engineering. One can identify the following sources of energy used in this kind of electroenergetics [1]: (1) solar (photovoltaic power); (2) wind energy; (3) energy of the Earth interior (high-temperature
geothermal energy); (4) ocean energy (energy of tides, waves, currents, temperature differences); and (5) energy of biomass (for electrical energy generation, a biogas is used).
The world technological capacity of renewable energy sources is estimated on the whole as follows (in billion tons of equivalent fuel a year): biomass, 5.6; hydraulic power, 2.8; wind energy, 2.8; geothermal energy; 1.9; thermal sea energy, 0.9; tidal energy, 0.04; solar cells and collectors (decentralized), 2.0; and solar power stations, 4.3. The total value is 20.3 billion tons of the equivalent fuel [2].
International Scientific Journal for Alternative Energy and Ecology № 3 (95) 2011
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The total power generated by all non-traditional sources by the end of 2008 was 280 gigawatts, including the following (gigawatts): wind power, 121; small hydropower, 85; biomass power, 52; solar photovoltaic, grid-connected, 13; geothermal power, 10; concentrated solar thermal power (CSP), 0.5; and ocean tidal power, 0.3. The five countries that are leaders in the generation of electric power from these sources were: China, the United States, Germany, Spain, and India [3].
For the present, the proportion of power generated by non-traditional sources in the world is absolutely insignificant and reaches 3.4% of all power generated [4]. However, its fast development (in 2006-08, the year-to-year increase reached 14-15%) made it possible to achieve noticeable results, at least in some countries.
For non-traditional renewable energy sources, the following features are characteristic: (1) low specific energy density; (2) severe difficulties in power concentration; (3) non-uniformity in its distribution in time and space; (4) difficulties of its use in power systems as a replacement power source; (5) rather high economic costs, even considering the absence of fuel costs; (6) operational in automatic mode; and (7) possibility of local use in hard-to-reach areas [5].
Main types of ocean energy and environmental consequences of its using
Main types of ocean energy are energy of tides, waves, currents, temperature and salinity differences. The extent of production engineering and costs of electric power generation from different energy sources differ markedly. Some of them do not at present find practical application, although their potential is very high.
Tidal energy
The magnitude of the tidal energy is closely related to range of tides. Zoning of the oceans on this indicator is shown in Fig. 1. Tidal power is a form of hydropower that converts the energy of tides into electricity. There are three basic types of tidal power plants: (1) tidal stream systems make use of the kinetic energy of moving water to power turbines, in a way that is similar to windmills using moving air; (2) barrages make use of the potential energy in the difference in height between high and low tides; they are essentially dams across the full width of a tidal estuary; (3) dynamic tidal power exploits a combination of potential and kinetic energy: by constructing dams 30-50 kilometres long from the coast straight out into the sea or ocean, without enclosing an area [6].
Рис. 2. SeaGen - первая промышленная электростанция, использующая кинетическую энергию приливных течений, Сев. Ирландия Фото: http://en.wikipedia.org/wiki/SeaGen, 14 мая 2008 Fig. 2. SeaGen, the world's first commercial tidal generator, in Strangford Lough, Northern Ireland. Photo credit: http://en.wikipedia.org/wiki/SeaGen, 14 May 2008
Рис. 3. Крупнейшая в мире приливная электростанция «Ля Ранс» (эстуарий р. Ранс, Северная Бретань, Франция) Фото: http://en.wikipedia.org/wiki/Rance_tidal_power_plant Fig. 3. La Rance, largest tidal barrage plant in the world (estuary of Rance river, Brittany coast of northern France) Photo credit: http://en.wikipedia.org/wiki/Rance_tidal_power_plant
The SeaGen tidal stream power station built in Strangford Lough (Northern Ireland) in 2007 can serve as an example of power stations of the first type (Fig. 2). A 1.2 megawatt underwater tidal electricity generator was installed here. The rates of tidal streams at this location reach 4 metres per second [7]. Such turbines have a minimal effect on the environment.
As for power stations of the second type, the tidal water is fed to a baffled-off basin. When the water levels in it and in the sea become equal, the gates at discharge openings are closed. With the onset of ebb tide, the sea water level drops and, at that time, turbines and electric generators connected to them come into action and water leaves the basin gradually [8].
Such tidal power plants can be double-acting. In this case, turbines work when water moves from the sea to the basin and vice versa. The double-acting tidal power plants are able to generate electric power for periods of 4-5 hours with interruptions of 1-2 hours four times a day [9].
The number of power stations using barrage tidal power also is not large. The La Rance plant (Fig. 3), off the Brittany coast of northern France, was the first and largest tidal barrage plant in the world. It was built in 1966 and has an output capacity of 240 megawatts. There are also several small power stations. For example, the Kislaya Guba Tidal Power Station (Barents Sea, Russia) was built in 1968 and, as of 2009, its output capacity was 1.7 megawatts [10]. The Annapolis Tidal Power Generating Station (Bay of
Fundy, North America) was completed in 1984; its output capacity is 20 megawatts [11].
The effects of the tidal power plant at the Bay of Fundy were analyzed in great detail, which is explained by the following: (1) long duration of discussion of its construction suitability (more than 70 years); (2) intense development of environmental legislation in the United States and Canada; (3) economic opportunities in these states; (4) considerable interest of the community in nature conservation; and (5) location of the bay on the border of two states that have responsibilities with regard to the plant [9].
The principal effect of tidal energy stations on the environment is a reduction of natural water exchange between the cut-off water body and the sea, which results in the following consequences: (1) changes in the distribution of current speeds in the bay; (2) redistribution of bottom sediments; (3) decrease in the aqueous medium stability in the bay (desalination, temperature rise, contamination, etc.) under the action of land processes; (4) decreases in the amplitude of the bay's water level variations; and (5) reductions in water turbidity [9, 12].
First of all, a tidal power plant affects hydrobionts because disturbances of exchange of salt and fresh waters, and redistribution of bottom sediments result in changes in the living conditions for sea flora and fauna. The investigations carried out in the La Rance tidal power plant showed an essential change in composition of bottom hydrobionts, but they did not record a drop
International Scientific Journal for Alternative Energy and Ecology № 3 (95) 2011
© Scientific Technical Centre «TATA», 2011
in their numbers [13]. At the same time, a sharp reduction in bioproductivity, a twofold decrease in the numbers of species of flora and fauna, and decreases in the total numbers of individuals were observed at Kislaya Guba [14].
A reduction of water turbidity increases the penetration of sunlight and the productivity of phytoplankton. Passage of fish through turbines results in their loss due to pressure drop, contact with blades, cavitation, and other causes. Even with the most fish-friendly turbine design, fish mortality per pass is approximately 15%. The loss of large marine mammals (whales, seals, dolphins, etc.) is possible [15]. In addition, the dams not infrequently prevent the renewal of fish resources, since the species that travel to the bays to spawn (salmon, herring, smelt, etc.) can not enter [14].
The environmental effects of tidal power plants are much less as compared with those of hydropower plants with similar output capacities.
The concept of tidal power plants of the third type was patented in 1997 by Dutch engineers K. Hulsbergen and R. Steijn. The power plants of this type not built yet, but potentially suitable sites for such construction are near the coasts of China, South Korea and the UK [16].
Wave energy
The wave power of the world ocean is estimated at 2.7 billion kilowatts [17]. For electricity generation, one can use wind-generated waves and surge. A peculiarity of sea disturbances is their inhomogeneity over time: maximum values are 5-11 times higher than average values [5]. Wave farm of Pelamis Wave Power Corporation is shown on Fig. 4.
Рис. 4. Испытания волновой электростанции фирмы Pelamis Wave Power у побережья Шотландии. Станция состоит из 4 секций диаметром 3,5 м, ее суммарная длина составляет 140 м. Фото: Pelamis Wave Power Fig. 4. Sea trials of a Pelamis machine near the estuary of Scotland's River Forth, where it flows into the North Sea. Each Pelamis machine is 140 metres long and 3.5 metres in diameter and is made up of four sections. Photo credit: Pelamis Wave Power
Spatial inhomogeneity is also characteristic of ocean disturbances (Fig. 5). Wave power flows are maximal within the coastal zones at high latitudes, and the wave energy density in the southern hemisphere is much higher than that in the northern hemisphere. The coasts in the low latitudes are characterized by comparatively small energy flows. The boundaries of sharp changes in the wave energy flow values for the Pacific coasts of North and South America, as well as for the American coasts of the Atlantic Ocean, pass along 30°N and 30°S. For the eastern Atlantic coasts, the boundary of abrupt change in the energy flow in the southern hemisphere shifts to 10°S [18].
150" 120* 90* 60* 30* О' 3d1 № 9C 120* 150' 180* 150*
Рис. 5. :iI ,:i .1 II.I полноной "аиергии (кВт на ногошшк метр фронта uvim,11 Публикуется с разрешения PelBDiis Wave Power. Fig. 5. Wave energy level (kilowatts permclre of wave Irani). Reproduced with permission of Pelamis Wave Power.
The average maximal density of wave energy is 40 megawatts per kilometre of coastline [19]. The extreme values are characteristic of the north-western coast of Great Britain in the vicinity of the Hebrides, where the wave energy density reaches 80 megawatts per kilometre [17]. On the whole, increased energy density is characteristic of the Pacific coastal zone, which is also extremely long. This index is slightly lower for the Atlantic and Indian Oceans [18].
There are three basic methods for converting wave energy to electricity:
1. Float or buoy systems that use the rise and fall of ocean swells to drive hydraulic pumps. The object can be mounted to a floating raft or to a device fixed on the ocean floor. A series of anchored buoys rise and fall with the waves. The movement 'strokes' an electric generator and produces electricity, which is then transmitted ashore by underwater power cables.
2. Oscillating water column devices in which the in-and-out motions of waves at the shore enter a column and force air to turn a turbine. The column fills with water as the wave rises and empties as it descends. In the process, air inside the column is compressed and heats up, creating energy the way a piston does. That energy is then harnessed and sent to shore by electric cable.
3. 'Tapered channel', or 'tapchan', systems rely on a shore-mounted structure to channel and concentrate the waves, driving them into an elevated reservoir. Water flow out of this reservoir is used to generate electricity, using standard hydropower technologies.
The world's first commercial wave energy plant was put into service in the Portuguese area of Agugadora on 23 September 2008. Its turbines provide a power of 2.25 megawatts. It is believed that the number of turbines (generators) in this plant can be increased in the future and that its capacity can be raised to 21 megawatts [20].
The influence of wave power engineering on the environment is not great and is expressed as follows: (1) variation in the dynamics of deposit movement within the coastal zone; (2) visual impact; and (3) indirect impact caused by high materials consumption of the wave energy plants.
The effect on deposit movement dynamics occurs when the wave energy plants are constructed within the coastal zone. The structures serve as breakwaters, disrupting the balance between erosion and accumulation of deposits. If the energy converters are placed in the deep waters of the open sea, the energy plants do not affect coastal stability [21].
The visual impact lies in the fact that, when wave energy plants are installed near a coastline, problems of aesthetic character arise because the plants are visible from shore. The indirect impact occurs because significant quantities of metals are melted to construct the wave energy plants, which is ecologically harmful.
In addition, the presence of a continuous line of wave energy plants may become a barrier for navigation and prove to be hazardous for ships under stormy conditions.
On the whole, wave power engineering is characterized by the least environmental impact of all the energy industries [22].
Osmotic energy
Of all kinds of oceanic energy, the reserves of osmotic energy are the highest. For its generation, two solutions with different salt concentrations are needed. The source of such energy is at the mouths of rivers. The world's first osmotic plant, with a capacity of 4 kilowatts, was opened by Statkraft on 24 November 2009 in Tofte, Norway [23].
The environmental consequences of operation of salt power plants are as follows [5]: (1) damage to living organisms in the course of water extraction or on membranes; (2) influence on freshwater species when waters of greater salinity are discharged; (3) variations in water circulation, which have an effect on the motion of nutrients and oxygen concentrations; and (4) penetration of toxic biocides used to prevent membrane contamination into the trophic chains.
Energy of oceanic currents
In particular, huge reserves of energy that can be transformed into electric power are concentrated in ocean currents. For example, the Gulf Stream carries a water volume exceeding 50 times the volume transported by all the rivers of the world. Based on the Gulf Stream, one could produce more than 100 million kilowatts of power. [5].
Currently, there are a number of projects of using energy of ocean currents to generate electricity. Most real is the project of building a power plant in the area of Bermuda. It is assumed that it will provide about 10% of the total electricity needs of this overseas territory of the UK [24]. There are projects of such power plants in the Straits of Florida and Gibraltar and off the eastern shore of Japan (Kuroshio Current).
Areas of the oceans which are most favorable for the construction of such plants are shown in Fig. 6. The cost of such electric power is so far too high. In addition it should be noted that many of these sites are areas of heavy traffic and turbines should be located with the maximum draft of vessels.
The impact of such plants on the environment while not completely investigated. It is obvious that the main factors of this effect will be the death of fish and large marine mammals due to contact with the blades of turbines and the changing nature of water circulation, which may affect the status of some species of aquatic organisms.
Energy of temperature differences
Another important potential source of energy is the temperature drop caused by the fact that solar radiation does not penetrate deep into the ocean waters and, therefore, cold waters are at shallow depths below the warm layer. Power plants that take advantage of these temperature differences may use the heat of surface
International Scientific Journal for Alternative Energy and Ecology № 3 (95) 2011
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waters to transform cooling fluid into steam (vapour). The cold water from depths of some hundred metres will cool and condense this steam (vapour), forming a low-pressure zone to which new portions of steam (vapour) will move, rotating the turbines [25].
The use of similar power plants can result in changes in water circulation, disturbances in the biological
balance, and climate change. In order to construct such power plants, large quantities of non-ferrous metals (magnesium, titanium, etc.) and new synthetic materials whose production is related to serious environmental contamination will be needed. The rise of deep waters rich in nutrients may have a favourable effect on organisms in surface waters.
150* 120* 90* 60* 30* 0' 30* 60* 90* 120* 150' 180* 150*
Рис. Ь. Районы Мирового океана, наиболее благоприятные для сооружения тлсЕстросташшй, испипьтушитх "энергию океанических течений.
Составлена ангорой нн основе данных J.S, Kenny (2007)
Fig. 6. Marine areas most favourable for construction of electric nations using energy of oceanic currents. Computed by author with wiih the use of data I'S Kenny {2007}
Conclusion
Currently, the use of ocean energy to generate electricity very slightly, but its potential reserves are very large. Obviously, that will happen gradually increase their importance in the global energy production. In terms of impact on the natural components of wave and tidal power are the most environmentally "clean" of all kinds of energy.
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International Scientific Journal for Alternative Energy and Ecology № 3 (95) 2011
© Scientific Technical Centre «TATA», 2011
