Tidal Turbines and Waves of the Future - Term Paper Example

Abstract Tides ebb and flow everyday and will continue to repeat this behaviour forever. It contains a lot of energy in itself which when harnessed by any means can generate electricity. There are two ways of generating tidal power by making tidal barrages or by utilising tidal streams in the sea. In case of barrage four main components are used for generation of power which is turbines, sluices, lock and embankments. Tidal streams are converted into electricity by three new technology; they are Tidal fences, Tidal turbines, and Tidal lagoons. Tidal Barrage has environmental effects but Tidal fences, lagoons and turbines have less environmental effects. There are approximately 20 sites over the world where tidal power can be generated. This energy is free, but it can be managed with any other power generation plant as it is available only for 10-12 hours per days when tides flows. Keywords: Tide, tidal, turbines, sluices, lock, embankments, tidal fences, tidal lagoons, tidal streams, Bulb turbine, Rim Turbine, Tubular turbine, Offshore Turbines, Vertical-Axis turbines and tidal barrages. I. Introduction One can easily say or predict that one thing happens every day twice, which is coming and going of tide in ocean (sea). This can happen because of gravitational force of the Moon and Sun at the same time rotation of Earth [3]. Because of tide huge of amount of water moves and harnessing it by some means can provide a great deal of energy. This energy supply is reliable and plentiful (forever) and renewable. The tides will continue to ebb and flow, and the energy is there for the taking. It gives a distinct advantage over other renewable sources that are not reliable and predictable, such as wind and solar energy. But the main concern is related to converting it into useful form of power (electricity) and that is not easy. Only around 20 sites in the world have been identified as possible tidal power stations [2]. Figure 1: Gravitational effect of the Sun and the Moon on tidal range Sourced: (ACRE) Australian CRC for Renewable Energy LTD II. Tidal Power (Technology) The power from tide can be generated by the two means. The first way is by using a Tidal Barrage and the other is by utilising the tidal streams in oceans. Tidal Barrage A tidal barrage is deigned to extract energy from the rise and fall of the tides and has only four main components [1], which are described below: Turbines: It is located in water passages which are designed to convert the potential energy of the difference in water levels across the barrage into kinetic energy in the form of fast-moving water and than later converted into rotational energy by the blades of the turbines and then into electricity by generators driven by turbines[1]. Different types of turbines used are Bulb turbine, Rim Turbine, Tubular turbine, Offshore Turbines and Vertical-Axis turbines [3][4]. The power available from the turbine at any particular instant is given by: Figure 2: Power Generation Calculation Model Where, Cd = Discharge Coefficient A = Cross sectional area (m2) G = gravity = 9.81 r = density (kg/m3) The equation above illustrates how important the difference between the water levels of the sea and the basin, (Z1-Z2), is when calculating the power produced [3]. Opening fitted with controlled gates (Sluices): It is designed to pass large flows under modest differential heads and have dual role; during construction, they allow the tides to continue to flow into and out of the basin behind the barrage with relatively little obstruction and thus enable the last parts of barrage to be built without undue difficulty. Once the barrage is in operation, they refill the basin (or empty it) ready for the next power generation period. Lock or similar Apparatus: It enables ships or boats to pass safely across the barrage after it complete. Embankments: It is a simple concrete caisson, which fill the remaining gaps across the barrage after it is complete. These have to be reasonably ‘opaque’ to water flow so that water and energy are not wasted [1]. Tidal Streams Tidal Stream power generation technology is still in its early years despite the potential for a reliable and predictable source. Tidal streams are fast flowing volumes of water caused by the motion of the tide. These usually occur in shallow of a sea where a natural constriction exists, which forces the water to speed up. This is somewhat similar to wind energy. The difference from wind energy is that water is 800 times denser than air and also it has a much slower flow-rate, which makes turbines experience much larger forces and momentum. This is why turbines have small diameter. But as it is similar to wind power technology so experience of that can be used for generation of power from tidal streams [3]. Energy can be captured from tidal streams using three methods, Tidal fences, Tidal turbines and Tidal Lagoons [4]. Tidal Fences: Tidal fences are somewhat similar to Tidal barrage; therefore Tidal fences share same environmental and social concerns. It has the electrical generators and transformers above the water. Figure 3: Artists impression of a tidal fence in operation (Courtesy of Blue Energy Canada) Tidal Turbines: Tidal turbines are less harmful to environment and are submerged in the water. They are out of sight that gives it many form of advantages over other tidal energy rivals (technology) It do not pose a problem for navigation and shipping and require less material in construction. Tidal turbines function best in areas where the water velocity is 2 - 2.5 m/s and above this level the turbine experiences heavy structural loads and below this not enough generation takes place or possible[3][4]. Figure 4: An Impression of Tidal Turbine Farm Figure 5: An artist’s impression of an axial flow, seabed mounted marine current turbine for shallow sea tidal power generation (courtesy of Tidal Stream) Tidal Lagoons: It is a new technology and is also called as offshore tidal power generation. It can resolve the environmental and economic problems of the familiar tidal barrage technology. Tidal lagoons use rubble mound impoundment structure and low-head hydroelectric generating equipment situated up to a mile or more offshore in a high tidal range area [4]. Figure 6: A tidal lagoon proposed for the Swansea Bay area in Wales (Courtesy of the BBC) III. Potential of Tidal Power: Advantages and Future Prospects According to Baker (1991), Tidal power resources around the world are Alaska, Argentina and Chile, Australia, brazil, Canada, China, France, India, Northern Ireland, South Korea, United States of America, United Kingdom and Russia [1][4]. The largest tidal power station in the world is in the Rance estuary in northern France and it is only one in Europe, which was built in 1966 [2]. Scotland has a definite potential for tidal stream energy to be converted to electricity and one area of focus is the Pentland Firth off the north coast. Tidal stream technology has the advantage over tidal barrages in view of environmental and ecological issues. Tidal stream technology is less intrusive Tidal Stream systems often have to be installed in difficult coastal waters and the installation and maintenance [3]. In September 2003, a subsea turbine manufactured by research and development firm Hammerfest Strom was anchored in Norway’s Kvalsund Chanel and began generating electricity for the small nearby city of Hammerfest. The submerged turbine looks like a cross between an airplane propeller and a windmill, with three 10-meter blades that turn with the tides to produce up to 3000 kilowatts (KW) of electricity, enough to light and heat about 35 Norwegian homes. If the pilot project is successful, Hammerfest Strom plans to install up 20 additional turbines in the area that would produce a minimum of 700 kW each [6]. Residents of Britain’s Devon coast, where two British companies have teamed to build the world first offshore tidal energy turbines, will be the first to benefit from these new tidal technologies. Sited about a mile offshore of Lynmouth, the single 11-meter blade will be capable of generating 300 kW of electricity, enough to power about 75 homes. “We estimate that there are at least 10 gigawatts of power available in the form of tidal power in the U.K.” Martin Wright of Marine Current Turbines Ltd., told BC news in June 2003 [7]. Tidal power (electricity) generation is totally dependent on tides flowing (in or out) and usually it can generate power 8-12 hours per day. This is because the rotational period of moon is around 4 weeks (28 days) and one rotation of earth takes 24 hours, therefore average tide cycle results in a tidal cycle of around 12.5 hours. For continuous power/electricity generation it can be managed along with other power station that can generate power when tidal power station is idle or not generating powers. Some advantages of Tidal power generations are: It can take only initial development cost, after that it is totally free(expect maintenance which is very less and operational cost) It is safe for the environment (as it needs no fuel) from the point of view of that; it produces no greenhouse gases or other waste. Tidal power produces electricity reliably and tides can be predicted easily. Offshore turbines and vertical-axis turbines are not ruinously expensive to build and do not have a large environmental impact. The disadvantages of tidal power are that barrage across an estuary is very expensive to build, and affects a very wide area. Because of barrage, the environment is changed for many miles upstream and downstream. This can affect many birds that rely on the tide uncovering the mud flats so that they can feed. Also there are limited sites for tidal barrages, which are approximately 20. One more disadvantages of tidal power are that it can provide only 10-12 hour electricity every day, when the tide is actually moving in or out. Therefore it can be not used independently and has to be managed along with other sources of power generation [2]. IV. Conclusion In conclusion, it can be said that tidal power is a very useful and can be managed with other power generation sources for generating electricity. It is free and it will be available till the planet exists. It has also less environmental effects (tidal streams) as compared to other power generation methods. References 1. Baker, A.C. “Tidal Power”, Peter Peregrinus Ltd., London, 1991. p.195, Chapter 2. 2. "Tidal power - energy from the sea", http://home.clara.net/darvill/altenerg/tidal.htm accessed on 17 January 2007 3. "Tidal Power", http://www.esru.strath.ac.uk/EandE/Web_sites/01-02/RE_info/Tidal%20Power.htm accessed on 17 January 2007 4. Lyon, K., McHenry, M. (and others)."Tidal Energy Systems", 2006, http://wwwphys.murdoch.edu.au/rise/reslab/resfiles/tidal/text.html accessed on 17 January 2007 5. "Renewable Technology", http://www.nef.org.uk/powered/documents/renewablespresentation.pdf accessed on 17 January 2007 6. Freeman, Kris. "Tidal Turbines: Waves of the Future?" Environmental Health Perspectives, Jan2004, Vol. 112 Issue 1, pA26-A26, 1/2p. 7. Lortie, Bret. "A new wave of energy" Bulletin of the Atomic Scientists, Nov/Dec2003, Vol. 59 Issue 6, p8-9, 2p, 1c. Read More