Tidal and wave energy
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Tidal and wave energy

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This report discusses the potential contribution that energy derived from the tides and waves can make to overall energy supply in a sustainable way. It covers the topics of wide range like how tides and waves are formed; functions of the possible and popular power generation systems especially tidal barrages,turbines, oscillating water columns and wave farms. Advantages and disadvantages of tidal and wave energy are also briefly discussed. Some cost data’s used give us brief insight into the economic prospects of the tidal and wave energy. By turning to potential along the Indian coastline, we found that India do have a huge potential of tidal and wave energy, though it has started very late. Government
initiatives and extensive research focused on the mentioned relevant opportunities will surely change the energy scenario.

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Tidal and wave energy

  1. 1. TIDAL AND WAVE ENERGY Rithin Nalli, Akash Ukey, Mukul Kumar ,Debabrot Bhuyan, and Pavan Kishan Bhukya * Department of Chemical engineering, Indian Institute of Kharagpur Kharagpur-721302, India. E-mail: rithin.ritz789@gmail.com E-mail: ukeyakash@gmail.com E-mail: mukul7835@gmail.com E-mail: debabrot91@gmail.com E-mail: bpavankishan1@gmail.com ABSTRACT: This report discusses the potential contribution that energy derived from the tides and waves can make to overall energy supply in a sustainable way. It covers the topics of wide range like how tides and waves are formed; functions of the possible and popular power generation systems especially tidal barrages, turbines, oscillating water columns and wave farms. Advantages and disadvantages of tidal and wave energy are also briefly discussed. Some cost data’s used give us brief insight into the economic prospects of the tidal and wave energy. By turning to potential along the Indian coastline, we found that India do have a huge potential of tidal and wave energy, though it has started very late. Government initiatives and extensive research focused on the mentioned relevant opportunities will surely change the energy scenario. Tidal Energy > 1. INTRODUCTION Tidal energy is a form of hydropower that converts the energy of the tides into electricity or other useful forms of power. The tide is created by the gravitational effect of the sun and the moon on the earth causing cyclical movement of the seas. Tidal energy is therefore an entirely predictable form of renewable energy.[1]
  2. 2. It’s a plain fact that we are in a world where almost 80 percent of the demanding energy is furnished by sources such as natural gas, coal, or oil, which are quickly being depleted as well as being environmentally unfriendly. We have also developed some destructive processes such as the nuclear power plants, which would also be a sword of Damocles of all human beings. Luckily, we have already realized the importance of making an enormous change in our way of life and our way of using the energy, so looking for renewable resources to substitute current ones is much urgent for us. Tidal power is classified as a renewable energy source, because tides are caused by the orbital mechanics of the solar system and are considered inexhaustible within a human timeframe. Energy from tidal power is also a form of pollution free energy, which has a lot of potential. Though these potentials have not been fully realised yet, we can’t deny the advantage of such kind of a renewable energy. This paper gives some basic introductions of tidal power and the basic principle of how tidal generator works, and it also focuses on the development of tidal power energy of the world. 2. HISTORY Tidal energy is one of the oldest forms of energy used by humans. Indeed, tide mills, in use on the Spanish, French and British coasts, date back to 787 A.D. but it is likely that there were predecessors lost in the anonymity of prehistory. Tide mills consisted of a storage pond, filled by the incoming (flood) tide through a sluice and emptied during the outgoing (ebb) tide through a water wheel. The tides turned waterwheels, producing mechanical power to mill grain and power was available for about two to three hours, usually twice a day. The power requirements of the industrialized world dwarf the output of the early tidal barrages and it was not until the 1960’s that the first commercial-scale modern-era tidal power plant was built, near St. Malo, France. The hydro mechanical devices such as the paddlewheel and the overshot waterwheel have given way to highly-efficient bulb-type hydroelectric turbine/generator sets. The tidal barrage at St. Malo uses twenty-four 10-megawatt low-head bulb-type turbine generator sets. Installed in 1965, the barrage has been functioning without missing a tide for more than 37 years.After that, more and more commercial- scale tidal barrage was put in service in France,Canada, Switzerland, UK, China and so forth. 3. Physical Concepts of Tidal Phenomena Tidal movements in seas are due to the increase of water levels at certain areas in the globe and the decrease of water levels at other areas. This is basically due to two factors: 1- The gravitational forces between the Sun, Moon and Earth. 2- The rotation of the moon and earth. [ Figure: http://teachearthscience.blogspot.in/2009/03/spring-tide-vs-neap-tide.html. ] As there are gravitational forces between the Moon and the Earth, seas or oceans water is pulled away from earth toward the moon at the area where the moon and the earth are in front of each other. At the
  3. 3. opposite side of the earth the water is being pushed away from the earth due to centrifugal forces. Thus as shown in Fig. there are two areas where the water levels are high and other areas where the water level is low. Thus, the tidal motion of water is created. This is called the lunar tide. The same concepts that apply for the moon apply for the sun, yet, the sun has a smaller effect on the water levels but when that can only contribute or lessen the effect of the moons gravitational power. This is described by "spring tides" where the lunar tide and solar tide are aligned and contribute to each other and by "neap tides" where the lunar and solar tides are at right angles of each other and lessen each other. 4. Sustainability of Tidal Energy Tidal energy represents an exciting new development in the renewable energy sector. Building on the success of other innovative renewable energy projects that generate energy from natural elements including water, wind and sun, tidal energy has the potential to contribute to the renewable energy solution required to tackle climate change. Tidal energy is a particularly clean, reliable and sustainable source of renewable energy. Generating tidal energy means: • more accurate energy planning resulting from an increased capacity to predict supply over the long term; • no visual impact as the underwater turbines cannot be seen from our coastlines; • Australia’s greenhouse gas emissions will be reduced; and • existing natural resources can be harnessed to produce clean and green energy. 5. Production of Electricity As usual, the electricity is provided by spinning turbines.Two types of tidal energy can be extracted: kinetic energy of currents between ebbing and surging tides and potential energy from the difference in height (or head) between high and low tides. The potential energy contained in a volume of water is E = xMg Where, x is the height of the tide, M is the mass of water and g is the acceleration due to gravity. Therefore, a tidal energy generator must be placed in a location with very high-amplitude tides. Suitable locations are found in the former USSR, USA, Canada, Australia, Korea, the UK and other countries • The generation of electricity from tides is very similar to hydroelectric generation, except that water is able to flow in both directions and this must be taken into account in the development of the generators. • The simplest generating system for tidal plants, known as an ebb generating system, involves a dam, known as a barrage across an estuary. • Sluice gates on the barrage allow the tidal basin to fill on the incoming high tides and to exit through the turbine system on the outgoing tide (known as the ebb tide). • Alternatively, flood-generating systems, which generate power from the incoming tide are possible, but are less favored than ebb generating systems. 6. How it Works? The rise and fall of the sea level can power electric-generating equipment. The gearing of the equipment is tremendous to turn the very slow motion of the tide into enough displacement to produce energy. Tidal barrages, built across suitable estuaries, are designed to extract energy from the rise and fall of the tides, using turbines located in water passages in the barrages. The potential energy, due to the difference in
  4. 4. water levels across the barrages, is converted into kinetic energy in the form of fast moving water passing through the turbines. This, in turn, is converted into rotational kinetic energy by the blades of the turbine, the spinning turbine then driving a generator to produce electricity. The diagram demonstrates power generation cycle of a tidal power. The highest output is achieved from hydroelectric turbines by operating when theavailable head is highest. The available head is highest at extreme low tide and extreme hightide. These periods are roughly two hours in length, but there is relatively little change in water level during the half hour preceding and the half hour after each of the extreme lows and highs. By including these 30-minute “shoulder” periods, a 3-hour generation period is achieved twice per tidal cycle. Thus, one can effectively generate at optimum levels for roughly half of each tidal cycle. Unfortunately, tidal cycles do not correspond to daily cycles of demand for electricity. 7. Tidal Power generation system In very simple terms a barrage is built at the entrance of a gulf and the water levels vary on both sides of the small dam. Passages are made inside the dam and water flows through these passages and turbines rotate due to this flow of water under head of water. Thus, electricity is created using the turbines. A general diagram of the system is shown below. COMPONENTS of a Tidal Power Station- Barrage: a barrage is a small wall built at the entrance of a gulf in order to trap water behind it. It will either trap it by keeping it from going into the gulf when water levels at the sea are high or it will keep water from going into the sea when water level at the sea is low. Turbines: they are the components responsible for converting potential energy into kinetic energy. They are located in the passage ways that the water flows through when gates of barrage are opened. • A bulb turbine is one in which water flows around the turbine. If maintenance is required then the water must be stopped which causes a problem and is time consuming with possible loss of generation. The La Rance tidal plant near St Malo on the Brittany coast in France uses a bulb turbine. • When rim turbines are used, the generator is mounted at right angles to the to the turbine blades, making access easier. But this type of turbine is not suitable for pumping and it is difficult to regulate its performance. One example is the Straflo turbine used at Annapolis Royal in Nova Scotia.
  5. 5. • Tubular turbines have been proposed for the UK’s most promising site, The Severn Estuary, the blades of this turbine are connected to a long shaft and are orientated at an angle so that the generator is sitting on top of the barrage. The environmental and ecological effects of tidal barrages have halted any progress with this technology and there are only a few commercially operating plants in the world, one of these is the La Rance barrage in France. Sluices: sluice gates are the ones responsible for the flow of water through the barrage they could be seen in Tidal Power station Fig. Embankments: they are caissons made out of concrete to prevent water from flowing at certain parts of the dam and to help maintenance work and electrical wiring to be connected or used to move equipment or cars over it. 8. ENERGY Calculations- TIDAL BARRAGE The energy available from barrage is dependent on the volume of water. The potential energy contained in a volume of water is: [2] E=1/2 Apgh2 where: h is the vertical tidal range, A is the horizontal area of the barrage basin, ρ is the density of water = 1025 kg per cubic meter (seawater varies between 1021 and 1030 kg per cubic meter) and g is the acceleration due to the Earth's gravity = 9.81 meters per second squared. The factor half is due to the fact, that as the basin flows empty through the turbines, the hydraulic head over the dam reduces. The maximum head is only available at the moment of low water, assuming the high water level is still present in the basin. 9. POWER Calculations- TURBINES The energy available from these kinetic systems can be expressed as: where: = the turbine power coefficient P = the power generated (in watts) = the density of the water (seawater is 1027 kg/m³) A = the sweep area of the turbine (in m²) V = the velocity of the flow Advantages of Tidal Energy Disadvantages of Tidal Energy Renewable resource, it needs no fuel to maintain, and free of charge. Totally no pollution, unlike fossil fuels, it produces no greenhouse gases or other waste. Predictable source of energy (compared with wind and solar), it is independent of weather and climate change and follows the predictable relationship of the lunar orbit. More efficient than wind because of the density of water. It will protect a large stretch of coastline against damage from high storm tides. Presently costly, very expensive to build and maintain.(A 1085MW facility could cost about 1.2 billion dollars to construct and run) Barrage has environmental affects -fish and plant migration -Silt and mud deposits -Waste and sewage blocks Technology is not fully developed. Only provides power for around 10 hours each day, when the tide is actually moving in or out.
  6. 6. (Relative to an open turbine in free stream, ducted turbines are capable of as much as 3 to 4 times the power of the same turbine rotor in open flow.) Large scale Tidal power plant : The largest barrage tidal power station of the world— Rance Tidal Power Station Rance Tidal Power Station is located on the estuary of the Rance River, in Brittany, France. Opened on the 26th November 1966 and is the largest tidal power station in the world, in terms of installed capacity. With a peak rating of 240 Megawatts, generated by its 24 turbines, it supplies 0.012% [3] of the power demand of France. With a capacity factor of approximately 40%, it supplies an average 96 Megawatts, giving an annual output of approximately 600 GWh. The barrage is 750 m (2,461 ft) long, from Brebis point in the west to Briantais point in the east. The power plant portion of the dam is 332.5 m (1,091 ft) long. Jiangxia power station is the largest tidal power station in China and thethird largest tidal power station in the world, which has been put into operation for nearly 20 years. The Annapolis Tidal Generating Station, located in Annapolis Royal and completed in 1984.The only modern tidal plant in North America. The above table from reference [4]. Asia's first commercial-scale tidal power station: The company Atlantis [5]Resources Corporation is to install a 50MW tidal farm in the Gulf of Kutch on India’s west coast, with the construction starting early this year. The company has signed a MoU with the government of Gujarat to set up the power plant by 2013. The plant is likely to be scaled up to a capacity of 250 MW at a cost of about $165 million[4]. The project will be developed in partnership with the Gujarat Power Corporation Limited. Advantages of Wave Energy Disadvantages of Wave Energy 1. It is free. Waves generated by the wind are used to convert into energy. 2. No waste products are produced. Thus no pollution is caused. 3. The running costs required to maintain and operate the facility is very less. 4. Significant amount of energy can be produced. 5. Due to which it helps in decreasing the dependence on non-renewable resources. 1. Energy output is variable depending on the height of the wave. 2. A suitable location is needed for the site, where the waves have to be strong. 3. Some designs are noisy, which may cause disturbances on the sea floor and to marine ecosystems. This noise can also be a problem to the people living close to it. 4. Equipment might not be able to withstand rough weather. 5. The initial capital costs required to develop is very high. 6. Wave energy devices located near or on the shore may degrade the scenic view in a tourist hotspot.
  7. 7. Among the various forms of energy contained in the seas and oceans, tidal energy, has been developed on a commercial scale. India has a long coastline with the estuaries and gulfs where tides are strong enough to move turbines for electrical power generation. The Gulf of Cambay and the Gulf of Kutch in Gujarat on the west coast have the maximum tidal range of 11m and 8m with average tidal range of 6.77m and 5.23m respectively. The Ganges Delta in the Sundarbans is approximately 5m with an average tidal range of 2.97m. The identified economic power potential is of the order of 8000 MW with about 7000 MW in the Gulf of Cambay, about 1200 MW in the Gulf of Kutch in the State of Gujarat and about 100 MW in the Gangetic Delta in the Sunderbans region in the State of West Bengal. Potential along the Indian coastline:- Power generation in India is mainly from hydroelectric and thermal power plants. The present total installed capacity hardly meets the grid demand. Uncertainty of the monsoon and problems of coal transport put a strong limitation on expansion of present generation capacity. Thus India needs to develop other sources of power like the power from the waves. The potential along the 6000 Km of coast is about 40,000 MW [7]. This energy is however less intensive than what is available in more northern and southern latitudes. Even 15% utilization would mean the availability of approximately 6000 MW. Generally it has been observed that the western coast is more useful than the eastern coast. This is because the former has more stable waves and is less vulnerable to cyclones that can damage the power plant. A wave atlas published by the National Institute of Oceanography (NIO) in Goa based on the swell data published in the Indian Daily Weather Reports (India Meteorological Department) gives the nationwide distribution of wave parameters. The average wave power potential along the Indian coastline is 5kWm-1 to 10kWm-1.[8] On the basis of scientifically collected data at Valliathura near Thiruvananthapuram on the Kerala coast, the average wave power works out to be 13kWm-1. A similar study along the coast of Maharashtra has shown that there are some potential sites such as Vengurla rocks, Malvan rocks, Redi, Pawas, Ratnagiri and Girye, possessing an average annual wave energy potential of 5 to 8 kW/m and monsoon potential of 15 to 20 kW/m.[6] Considering this, the total potential along the 720 km-stretch of Maharashtra coast is approximately 500 MW for wave energy power plants. WAVE ENERGY > Ocean wave energy (as distinct from internal waves or tsunamis) is energy that has been transferred from the wind to the ocean. As the wind blows over the ocean, , air-sea interaction transfers some of the wind energy to the water, forming waves, which store this energy as potential energy (in the mass of water displaced from the mean sea level) and kinetic energy (in the motion of water particles). The size and period of the resulting waves depend on the amount of transferred energy, which is a function of the wind speed, the length of time the wind blows (order of days) and the length of ocean over which the wind blows (fetch). Waves are very efficient at transferring energy, and can travel long distances over the ocean surface beyond the storm area and are then classed as swells (Barber and Ursell, 1948; Lighthill, 1978). The most energetic waves on earth are generated between 30º and 60º lati- tudes by extra-tropical storms. Wave energy availability typically varies seasonally and over shorter time periods, with seasonal variation typi-cally being greater in the northern hemisphere. Annual variations in the wave climate are usually estimated by the use of long-term averages in modelling, using global databases with reasonably long histories. The total theoretical wave energy potential is estimated to be 32,000 TWh/yr (115 EJ/yr) (Mørk et al., 2010), roughly twice the global electricity supply in 2008 (16,800 TWh/yr or 54 EJ/yr). This figure is unconstrained by geography, technical or economic considerations. The regional dis-tribution of the annual wave energy incident on the coasts of countries or regions has been obtained for areas where theoretical wave power P ≥ 5 kW/m and latitude ≤66.5º (Table 6.1). The theoretical wave energy potential
  8. 8. listed in Table 6.1 (29,500 TWh/yr or 106 EJ/yr) represents a technical developments in wave energy devices. Sims et al. (2007) esti-mate a global technical potential of 500 GW for wave energy, assuming that offshore wave energy devices have an efficiency of 40% and are only installed near coastlines with wave climates of >30 kW/m, whereas Krewitt et al. (2009) report a wave energy potential of 20 EJ/yr. A range of devices are used to measure waves: • Wave-measuring buoys are used in water depths greater than 20 m (see Allender et al., 1989). Seabed-mounted (pressure and acoustic) probes are used in shallower waters. Capacity/resistive probes or down-looking infrared and laser devices can be used when offshore structures are available (e.g., oil or gas platforms) • Satellite-based measurements have been made regularly since 1991 by altimeters that provide measurements of significant wave height and wave period with accuracies similar to wave buoys (Pontes and Bruck, 2008). The main drawback of satellite data is the long interval between measurements (several days) and the corresponding large distance between adjacent tracks (0.8º to 2.8º along the Equator) • The results of numerical wind-wave models are now quite accurate, especially for average wave conditions. Such models compute direc-tional spectra over the oceans, taking as input wind fields provided by atmospheric models; they are by far the largest source of wave information. Table 1 | Regional theoretical potential of wave energy (Mørk et al., 2010). REGION Wave Energy TWh/yr (EJ/yr) Western and Northern Europe 2,800 (10.1) Mediterranean Sea and Atlantic Archipelagos (Azores, Cape Verde, Canaries) 1,300 (4.7) North America and Greenland 4,000 (14.4) Central America 1,500 (5.4) South America 4,600 (16.6) Africa 3,500 (12.6) Asia 6,200 (22.3) Australia, New Zealand and Pacific Islands 5,600 (20.2) TOTAL 29,500 (106.2) Modern technology Wave power devices are generally categorized by the method used to capture the energy of the waves, by location and by the power take-off system. Method types are point absorber or buoy; surfacing following or attenuator oriented parallel to the direction of wave propagation; terminator, oriented perpendicular to the direction of wave propagation; oscillating water column; and overtopping. Locations are shoreline, nearshore and offshore. Types of power take-off include: hydraulic ram, elastomeric hose pump, pump-to-shore, hydroelectric turbine, air turbine, and linear electrical generator. Some of these
  9. 9. designs incorporate parabolic reflectors as a means of increasing the wave energy at the point of capture. These capture systems use the rise and fall motion of waves to capture energy. Once the wave energy is captured at a wave source, power must be carried to the point of use or to a connection to the electrical grid by transmission power cables. The table contains descriptions of some wave power systems: DEVICE COUNTRY LOCATION POWER TAKE OFF YEAR Aquabuoy Canada , Ireland Offshore Hydroelectric Turbine 2003 Ceto Wave Power Australia Offshore Pump to shore 2000 Islay LIMPET Scotland Onshore Air Turbine 2001 OWEL UK Offshore Air Turbine 2013 Economic Prospects of tidal and wave energy Key factors affecting cost of energy. Commercial markets are not yet driving marine energy technology development. Government-supported R&D and national policy incentives are the key motivation for most technology development and deployment. The cost of most ocean energy technologies is difficult to assess, because very little fabrication and deployment experience is available for validation of cost assumptions. Due to the very limited amount of historic data there are no learning curves available for ocean energy technologies. The costs of energy of marine renewables technologies depend on several factors. Principally, these include capital costs, operating and maintenance (O&M) costs and the amount of electricity produced (performance). Like wind energy, wave and tidal stream energy are free at source so there is no fuel cost. Essentially, capital costs and O&M costs must be weighed against performance, since this is the saleable output and represents income to the generator. A high performance device can afford to be expensive if its costs are more than met by the value of electricity sold. But if the costs are so great that they exceed the income from generation, the device will not be economically viable. The balance of costs and performance is manifested in the cost of energy, and the target for this is the cheapest alternative: another form of renewable or conventional power generation. 1. Capital cost 2. Operating and maintenance costs The capital cost of marine renewables technologies can broken down into: (i) the cost of the generation device itself (materials, components and labor in manufacturing and fabrication processes); (ii) the costs associated with installing it (deployment); (iii) the costs of keeping it on station (foundations or moorings); and (iv) the costs of connecting it to the grid (electrical cables and switchgear). Some of these costs are more dominant than others, and the relative distribution of cost centers varies between different device concepts and site locations. The O&M costs of marine renewables can also be considered in several parts, including: (i) Maintenance, both planned and unplanned (like tsunami, sea storms etc.) ; (ii) overhauls; where it is most economical to re-fit components during the service life; (iii) licenses and insurance to allow the devices to be kept on station and to manage the associated risks; and (iv) Ongoing monitoring of wave or tidal conditions and the performance of devices. To have an approximated idea of the cost involved in the tidal and wave energy technology, We have this table [14].
  10. 10. Refit 24% Monit oring 4% Plann ed maint ena… Unpla nned maint ena… Insur ance 14% Licen ces 1% Type of OWC Locaions Cost ( in USD perkW)Cost (in USD per kW) First prototype model Near-shore 5000-15000 First production model Near-shore 2000-5000 First prototype model shoreline 9000-17000 First production model shoreline 2500-9000 It is evident from this table that production model costs around one-third of the prototype model. Then the following table shows the estimated costs of wave and tidal energy (in ¢/kWh) for current and future cases.[14] Cost Wave Energy Tidal Energy Current cost (in ¢/kWh) 10-30 8-12 Future cost (in ¢/kWh) 5-6 4-6 It is evident from this table that future costs will come down by around 50%, mainly due to technological improvement. It should be noted that figures for the future costs are comparable to current cost of conventional costs. It means, in future, tidal and wave energy will be strong substitute for the conventional energy resources. Breakdown of capital costs for a wave farm- Following is the pie chart showing the breakdown of the capital cost of a wave farm [15]. Here, we can note that mechanical and electrical costs around half of the whole capital cost and another one-fourth goes to structural cost. Breakdown of operation and maintenance costs for a wave farm-From this pie chart of operation and maintenance, we can note that almost half goes to maintenance sector and another one-fourth goes to refitting components.
  11. 11. Exhibit: Global Wave and Tidal Pipeline Capacity in Key Markets 2010-2015 (MW)- Here is the bar graph taken from IHS Emerging Energy Research, Global Ocean Energy Markets and Strategies: 2010-2030 [16] showing the estimated pipeline capacity for 2010-15 session market. It is to be noted here that India is at 2nd position in tidal pipeline capacity, but in wave pipeline capacity, it’s in bottom 3’s. This latter finding is really disturbing because despite India huge potential for wave power harnessing. The economic prize of Tidal and wave energy technologies- Now we try to explore the revenue and investment Due to uncertainties about future costs, estimates of the long-term economic potential of wave and tidal stream energy tend to be approximate. However, the resource estimates suggest there could be both major domestic and export markets for wave and tidal stream energy generation equipment, as well as site development, construction, installation and operation services. As indications of market size: It is estimated that the value of worldwide electricity revenues from wave and tidal stream projects could ultimately be between $100b/year and $ 300b/year [17] and Investments of over $ 800b would be necessary for wave energy to contribute 2000 TWh/year worldwide[E]. One important insight we get here is that revenue by investment ratio is around 1/8 to 3/8. In other words, 12.5% to 37.5% profit which is economically very attractive investment criteria. So, we can be sure that in recent days, more and more innovations is going to be happen in these sectors. Overall, the market for marine renewables, particularly offshore wave energy, is likely to be sufficiently large to merit considerable interest in its commercial development. Research opportunities- Through the report we have seen many disadvantages of both tidal and wave energy. It simply suggests that, those mentioned areas do need improvement and intensive research. Followings are the some points of having research opportunities- • Tidal and wave energy have the huge potential to meet worldwide energy need, but due to lack of means, we are still facing energy crisis. Further researches are being done and many innovative solutions are being tried. • The capital cost of initial construction of the tidal and wave energy devices are very high as we have seen in the breakdown pie-chart. Extensive research is taking place to achieve cheaper ways of tidal and wave energy harnessing.
  12. 12. • The construction of tidal power plant disrupts fish migration in the oceans, and even kills fish population when passing through the turbines. So, seabed sonar is being tried. The two state-of- the-art sonar systems monitor’s fish and diving seabirds that pass through or feed within the location, with the special emphasis on how fish and seabirds interact with wave and tidal power installations. • Grid remains a barrier to the development of the tidal and wave energy industry but researches are being done so that the improved access, innovation and scale can aid project development. • Current energy devices extract only small fraction of overall tidal and wave energy. Experts are trying to find ways to increase energy and exergy efficiency. • Maintenance costs are very high; causing the cost of energy high. Different algorithms are tried to reduce such costs. CONCLUSIONS- Ocean energy offers the potential for long-term carbon emissions reduction but is unlikely to make a significant short-term contribution before 2020 due to its nascent stage of development. In 2009, additionally installed ocean capacity was less than 10 MW worldwide, yielding a cumulative installed capacity of approximately 300 MW by the end of 2009. All ocean energy technologies, except tidal barrages, are conceptual, undergoing research and development (R&D), or are in the pre-commercial prototype and demonstration stage. The performance of ocean energy technologies is anticipated to improve steadily over time as experience is gained and new technologies are able to access poorer quality resources. Whether these technical advances lead to sufficient associated cost reductions to enable broad-scale deployment of ocean energy is the most critical uncertainty in assessing the future role of ocean energy in mitigating climate change. Though technical potential is not anticipated to be a primary global barrier to ocean energy deploy-ment, resource characteristics will require that local communities in the future select among multiple available ocean technologies to suit local resource conditions Though ocean energy resource assessments are at a preliminary phase, the theoretical potential for ocean energy easily exceeds present human energy requirement. One assessment places the global technical potential for 2050 at 331 EJ/yr, dominated by OTEC (300 EJ/yr) and wave energy (20 EJ/yr), whereas on the other end of the spectrum, another assessment lists the ‘exploit-able estimated available energy resource’ at just 7 EJ/yr. Whilst some potential ocean energy resources, such as ocean currents and osmotic power from salinity gradients, are globally distributed. Ocean energy systems are at an early stage of development, but technical advances may progress rapidly given the number of technology demonstrations. With the exception of tidal range energy, which can be harnessed by the adaptation of river-based hydroelectric dams to estuarine situations, most ocean energy technologies have not yet been developed beyond the prototype stage. Worldwide developments of devices are accelerating with a large number of prototype wave and tidal current devices under development. Government policies are contributing to accelerate the implementation of ocean energy technologies. Some national and regional governments are supporting ocean energy development through a range of initiatives, including R&D and capital grants to device developers; performance incentives for produced electricity; marine infrastructure development; standards, protocols and regulatory interventions for permitting; and space and resource allocation.
  13. 13. References: 1. 1.http://www.tidalenergyltd.com/?page_id=1370 2. 2.http://hydropower-tidalpower.blogspot.in/2009/07/energy-calculations_07.html 3. 3.http://en.wikipedia.org/wiki/Rance_tidal_power_plant 4. www.energeticindia.net/download.php?seccion=articles&archivo=83mjq81K2PCCP8laGPs6n2vtf. pdf. 5. http://www.bbc.co.uk/news/science-environment-12215065 6. http://www.mahaurja.com/PG_Wave.html 7. http://www.eai.in/ref/ae/oce/oce.html 8. http://www.ias.ac.in/jarch/currsci/60/00000701.pdf 9. http://en.wikipedia.org/wiki/Wave_power#Modern_technology 10. http://www.alternative-energy-news.info/technology/hydro/wave-power/ 11. http://www.darvill.clara.net/altenerg/wave.htm 12. http://www.carnegiewave.com/index.php?url=/ceto/global-wave-energy 13. http://www.rnp.org/node/wave-tidal-energy-technology. 14. Source: Entec, based on data provided by Atkins and Black & Veatch. 15. Source: IHS Emerging Energy Research, Global Ocean Energy Markets and Strategies: 2010- 2030 16. Source: Entec (2005) 17. ETSU (1999), A Brief Review of Wave Energy

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