Wave Energy

10 Key excerpts on "Wave Energy"

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  Future Energy

  Improved, Sustainable and Clean Options for our Planet

  • Trevor Letcher, Trevor M. Letcher(Authors)
  • 2008(Publication Date)
  • Elsevier Science

    (Publisher)

  Around this time the wind energy sector began to take off and hence Wave Energy was temporarily shelved. The current boom for Wave Energy started in the mid-1990s with several large-scale developments in Scotland, India, Japan and Portugal. The drivers for this boom started with carbon reduction targets but have evolved and matured now into such aspects as energy diversity and security of supply. Governments are starting to realize that a new energy crisis may be looming and the commercial sector is beginning to see the potential of being a first mover in this new energy economy. With planning becoming more difficult for onshore wind, and limited suitable sites for both offshore wind and tidal stream, the interest has again been ignited in the Wave Energy sector. 2. What is Ocean Wave Energy? There are many types of waves found in the ocean, both on the surface and below. These waves transfer energy away from their sources. Such sources of energy are excited by various forces ranging from gravitational forces through earthquakes and floating body interactions [1]. The focus of the Wave Energy sector, though, is the conversion of ocean wind waves. These wind waves are formed by winds blowing across large areas of ocean, with the surface friction transforming the energy. There are two types of wave that the Wave Energy converter is interested in: swell waves and local wind seas. Swell waves are generated from distant storms, whereas local wind seas are generated much closer to the point of inter-est. The size of the waves – and hence their energy – is a function of the wind speed in the storm area, the size of the storm area or ‘fetch’ and the duration of the storm. As the waves grow, their speed increases and eventually this will exceed the speed of the storm and so swell waves will arrive at a coastline before the storm arrives.

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  Ocean Energies

  Environmental, Economic and Technological Aspects of Alternative Power Sources

  • R.H. Charlier, J.R. Justus(Authors)
  • 1993(Publication Date)
  • Elsevier Science

    (Publisher)

  Waves 111 WIND WAVES The birth of waves Waves are generated by the force of the wind blowing over the ocean's surface. During a storm at sea, large waves are created, which move radially from the storm region. They travel virtually undiminished until they crash on a shore which could be thousands of miles away. The regular breakers seen on most beaches originate out at sea and could come from a variety of different storms. The water's surface acts as a great conveyer belt, delivering wave power from great distances. In this way wave activity is more consistent than wind activity and, thus, offers a steadier, more reliable form of energy. Even so, waves vary in several ways. The waves are larger in winter than in summer. They also vary from location to location. Where the winds are steady the waves persist for long periods of time. Waves are encountered worldwide on lakes, seas and oceans (Fig. 5.1). As all sailors know there are two bands of steady winds in each hemisphere corresponding to the easterly tradewinds, located 3 to 10 north and south of the equator and the westerlies at about 55 north and south (Fig. 5.1). The prime locations for utilizing Wave Energy are adjacent to coasts in these latitudes, such as Hawaii, the Pacific Northwest of the American continent, the British Isles and [ D O L D R U M S 0 Fig. 5.1. Global wind patterns. (From: Introduction to Oceanography, by David Ross. Prentice-Hall, Englewood Cliffs, NJ, 1977.) 112 Chapler 5 Norway, but many other good sites exist elsewhere including some in less developed countries (e.g. Mauritius). In addition to their variations with time and location, at a given point, waves also vary in their directions of travel. For some Wave Energy conversion devices this variation is important. Characteristics of waves A few minutes spent observing the ocean’s surface will reveal a highly complex, variable collection of waves that never repeats itself no matter how long we look.

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  Energy and the New Reality 2

  Carbon-free Energy Supply

  • L. D. Danny Harvey(Author)
  • 2010(Publication Date)
  • Routledge

    (Publisher)

  A long floating structure aligned parallel with the wave direction. Movements along its length can be selectively constrained to produce energy. It has a smaller area perpendicular to the waves than a terminator, so it experiences smaller forces

  4 Other 5

  Source: IEA (2006d)

  Table 7.1 outlines the various Wave Energy technologies under development and the number of projects of each type identified by IEA (2006d). The large number of different technologies still under development indicates that the level of understanding is not sufficiently advanced to show which concepts will be the most cost effective.

  Figure 7.2 illustrates two possible Wave Energy conversion devices: an onshore oscillating water column device and a floating ocean wave converter buoy. There are many concepts for floating offshore devices, all of which would be able to take advantage of the greater energy in waves in deeper water. These include the point absorber and various overtopping devices (in which waves spill into a slightly elevated floating basin, then drain through a low-head turbine).

  Figure 7.2

    Wave Energy conversion devices

  Note: Top, a shoreline ocean wave converter; bottom, a floating ocean wave convertor buoy

  Source: Khan and Bhuyan (2009)

  Wave Energy, like wind energy, is variable in time. However, the available Wave Energy can be accurately predicted 24–48 hours in advance through the use of satellite remote sensing of surface winds and wave heights over entire ocean basins. This in turn reduces the fossil fuel spinning reserve that would otherwise be required in most jurisdictions to rapidly compensate for fluctuations in power production (as discussed in Volume 1, Chapter 3 , subsections 3.1.6 and 3.2.6).

  7.3 Tidal Energy

  Tides are produced by the gravitational attraction of the moon and sun on the waters of the ocean. In fact, with regard to the moon, there are two factors at work: gravitational attraction as well as a centrifugal effect.

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  The Future of Energy Use

  • Geoff O'Brien, Nicola Pearsall, Phil O'Keefe(Authors)
  • 2010(Publication Date)
  • Routledge

    (Publisher)

  Wave Energy is extracted from ocean waves which are generated by the action of wind passing over a large stretch of water. Anyone who has been hit by a large wave knows how powerful they can be. The most powerful are those with a long period (the time taken for successive peaks to pass a given point) and great height, and they mainly occur in deep water because inshore waves lose much of their power through friction from the sea bed. Even so, coastal waves can have a very considerable average energy.

  Figure 7.40 shows the average annual energy per metre of wave in various parts of the world. As with other renewable energy technologies, the calculation of the resource relies on technology assumptions and an estimate of the percentage of the energy in waves that could be extracted economically. Wavenet, a network of experts on Wave Energy, have suggested a technical resource of 5–20TWh/year for near shore devices and 140–750TWh/year for offshore devices, the wide range reflecting the fact that the energy extraction depends on both the wave regime and the nature of the device (Wavenet, 2003).

  Energy in waves

  The energy in a wave consists of the kinetic energy of the moving water, and the potential energy associated with the peaks and troughs above and below mean sea level. For simplicity, let us consider a single wave with a wavelength λ (the distance from crest to crest) and a wave period T (the time between the passage of one crest and the following crest past a fixed point). The velocity at which the Wave Energy moves is given by V = gT/2π and the wavelength is related to the wave period by λ = VT = gT2 /2π.

  Figure 7.40 Average annual Wave Energy per metre at selected sites (MWh)

  In both these relationships, g is the acceleration due to gravity.

  The total energy per unit surface area of the wave is given by

  E = ½ρga2

  where ρ is the density of sea water and a is the amplitude of the wave (the height of the crest from mean sea level, or half the height from trough to crest). The power per metre length of wavefront is

  P = EV= (1/8π) ρg2 a2 T or

  P = 3.9a2 T (kW)

  when a is in metres and T in seconds.

  For a wave of 1m amplitude and a wave period of 10 seconds, the power/metre is then 39kW. The length of such a wave would be about 150m, so these are, for example, the long Atlantic rollers which sweep into the west coast of Great Britain.

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  Hydrodynamic Control of Wave Energy Devices

  • Umesh A. Korde, John Ringwood(Authors)
  • 2016(Publication Date)
  • Cambridge University Press

    (Publisher)

  1.4 Wave Energy As indicated earlier, the water particles under a wave perform an orbital motion around their static-equilibrium positions. It is through this motion of small elemental water masses that the energy in a wave at any point and any time manifests itself. Wave Energy is thus a combination of kinetic and potential energies. The total energy in the wave at an instant equates to the integral of the elemental particle energy at that instant over the water depth (or a portion of it, as wave action decreases exponentially with depth), the length of the wave (a “wavelength”), and the width of the crest (or trough) perpendicular to the plane of orbital motion. As this is a periodic function of time, it is customary to use the time-averaged energy, averaged over a wave period. Wave Energy is proportional to the square of the wave amplitude, to gravity acceleration and water density, as well as to the wavelength and the crest width (or “crest length”). Wave power is the rate of propagation of Wave Energy. In the deep sea, the longer a wave, the faster its energy propagates. While wave amplitudes at which conversion is practical tend to be less than 2–3 m, the corresponding wavelengths can range from 10 m (short seas) to over 300 m (long swells). Waves with 8 Wave Energy Conversion large amplitudes and short wavelengths tend to break and lose energy (and amplitude). Thus, over time, the Wave Energy content in a spectrum tends to be dominated by longer waves that can support greater amplitudes. A wave spectrum dominated by longer waves has a longer “energy period” and provides more energy to a device. As wavelength increases with the square of the wave period in deep water, and as wave period is easier to measure than wavelength (and wave height easier to measure than wave amplitude), wave power is frequently expressed just in terms of the square of the wave height and wavelength.

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  Marine Natural Resources and Technological Development

  An Economic Analysis of the Wealth from the Oceans

  • Marco Colazingari(Author)
  • 2013(Publication Date)
  • Taylor & Francis

    (Publisher)

  Waves are moved primarily by winds, which, in turn, are stimulated by solar energy. The different heating that the Earth receives from the sun produces low and high pressure in the atmosphere, which interaction produces winds. Winds transfer some of the energy to the water through friction between air and water molecules. The size of the waves depends on the wind speed, the length of time and the distance—or fetch—the wind blows. There are great variations in wave power level but in principles the power available in a wave is proportional to the square of the wave height (amplitude) and to the wave period, or period of motion. A commonly used yardstick to rate waves’ potential is the energy flux, which refers to the energy in kilowatt transported in each meter of wave crest length. Long- period, large-amplitude waves have an energy flux of 40–50 kW/m (CRES 2002). The global wave power potential, which is the greatest among marine renewable, has been estimated between 8,000 and 80,000 TWh per year (IEA 2003), corresponding to 1–10 TW. The World Energy Council estimates the wave potential at 2 TW (Thorpe 1999).

  Wave power varies seasonally and the wave resource at the development site is, of course, a critical factor in assessing the efficiency of the power plant. Wave Energy is at its strongest power in ocean depths of at least 50 m, before the wave loses energy because of the friction with a shallower seabed. The best locations for exploiting wave power are found at temperate latitudes between 30° and 60°. Waves considered useful for energy production vary from 40 to over 300 meters in length (EPRI 2004) and the best sites for wave-power plants must have more than 30 kW/m2 of wave power. More powerful waves (up to 70 kW/m and more) would destroy any device (see Figure 4.3 ).

  Figure 4.3 World Wave Energy Source. Wave Power in kW/m. Source: IEA-OES (2003).

  Wave Energy Converters (WECs) transform the kinetic energy of the moving water into electric power through a generator. The power input is the low-speed, high-force wave motion that must be converted to the highspeed, low-force power output of the electric generator. This mismatch can be overcome in different ways. Current technology is able to achieve power conversion by means of hydraulic, hydrodynamic and pneumatic devices. Even though there has been extensive research and development of WEC technology, it only began in the 1970s as a reaction to the oil crises and the subsequent rally of energy market prices. However, in France, way back in 1799, Girard & Son patented a technique to convert the ocean’s Wave Energy into a useful form of energy. In theory, as water is 832 times denser than air, it should be possible to get the same amount of energy from the water motion with a device much smaller and cheaper than a wind driven turbine. Although similar to wind turbines, underwater turbines are in fact much smaller and have a slower motion. On average, a water turbine has a dimension of about 9 m against the 90 m of a wind turbine and turns at about 30 rpm (revolutions per minute) against the 60 rpm of a wind turbine. In 1994 the EU Commission started a research program on WECs technology, including studies, financing projects with technical feasibility and the formation of the European Thematic Network on Wave Energy in order to coordinate collaborations among European countries. WECs are expected to provide in the near future an efficient, reliable, cost-effective and environmentally friendly source of electrical power. Some European governments, in particular the UK and the Scandinavian countries, have programs to develop this renewable energy sector by means of financing scientific research and experiment of prototypes.

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  New Developments in Renewable Energy

  • Hasan Arman, Ibrahim Yuksel, Hasan Arman, Ibrahim Yuksel(Authors)
  • 2013(Publication Date)
  • IntechOpen

    (Publisher)

  Section 5 Ocean Energy Chapter 12 Ocean's Renewable Power and Review of Technologies: Case Study Waves Ehsan Enferad and Daryoush Nazarpour Additional information is available at the end of the chapter http://dx.doi.org/10.5772/53806 1. Introduction In last decades, in effect of high price of fossil fuel, environmental pollution due to fossil fuel utilization and greenhouse effect, renewable energy resources are considered as an alterna‐ tive energy resource to the World’s excessive energy demand. Nowadays, different technol‐ ogies are utilized to energy generation from hydro power, fuel cell and hydrogen, biomass, geothermal, solar thermal, photovoltaic and wind, while the technology for converting ocean powers are still in infancy. The aim of this chapter is to introduce potential renewable power sources of ocean, mostly ocean wave power, as well as available technologies for ex‐ tracting wave power. Due to high energy amount available in ocean, the issue has a strong importance to investigate. Furthermore there are variety of technologies that are developed for harnessing wave power each of which has an individual mechanism. Harvesting ocean wave power and converting to electrical power is a challenge for marine, mechanical, elec‐ trical and control engineers and we hope to give essential information about ocean wave, methods of energy extracting from wave and related electrical equipment. 1.1. Ocean The oceans contain 97.2% of total world water which are covering 71% of Earth’s surface [1]. Also the oceans intrinsically are couple with atmosphere via air-water interface and they ex‐ change heat, moisture, momentum and trace constituents by means of air-water interface [2 ]. The fundamental processes that transfer energy from atmosphere to ocean are energy in‐ put to ocean by wind and net surface heat flux [3 ]. Furthermore, ocean absorbs heat of geo‐ thermal energy via geothermal vent in ocean bed.

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  Alternative Energy Systems

  Electrical Integration and Utilisation

  • Mike West, Peter White, Brian Loughridge, Mike West, Peter White, Brian Loughridge(Authors)
  • 2013(Publication Date)
  • Pergamon

    (Publisher)

  The economic analysis of the production of electricity on a significant national scale from Wave Energy reported in ETSU’s Strategic Review of the Renewable Energy Technologies showed that in 1982 it was unattractive when compared with competing technologies. Subsequent analysis has refined our understanding of Wave Energy economics while confirming the findings of the Strategic Review.The Harwell electricity supply system model has been used to recalculate breakeven costs, net present values and benefit/cost ratios in the same scenarios as used in the Strategic Review. Attention was focused on a 2 GW wave power station with an assumed annual load factor of 25% installed between 2001 and 2010 with a life of 25 years. Much of the analysis was carried out for this first wave power station but the sensitivities to the main assumptions and the economics of subsequent wave power stations were considered.This more recent economic analysis shows that while Wave Energy can appear cost-effective under particularly favourable scenarios using optimistic assumptions on costs and productivity, its overall economic prospects are not good. The analysis merely serves to strengthen the conclusion of the Strategic Review of the Renewable Energy Technologies that the economic prospects of Wave Energy are poor both in comparison with other renewable energy technologies and with conventional thermal plant. This suggests that wave power is only likely to be considered by a UK electricity board as some form of strategic option which could be relied upon if other more economically attractive generation options became unavailable for non-economic reasons. Its deployment would increase costs to the consumer in all scenarios considered.

  KEYWORDS Wave Energy economic analysis electricity generation

  INTRODUCTION

  The economic analysis of Wave Energy reported in the Strategic Review of the Renewable Energy Technologies (ETSU, 1982 ) showed that the economics of Wave Energy are unattractive when compared with competing technologies. This conclusion, which was the basis of the ACORD recommendation to run down the Wave Energy programme, has subsequently been confirmed by further economic analysis. The main findings of this analysis are presented in the Wave Energy Report (ETSU, in prep.) and the purpose of this note is to provide a more detailed documentation of this work.

  The direct costs of Wave Energy are the engineering costs of construction, operation and maintenance. These costs, while they may be subject to many uncertainties and difficulties of interpretation, are relatively easy to recognise and define. The Wave Energy Report gives detailed consideration to the various elements of costs, how they are estimated and the uncertainties in these estimates. The net benefit of Wave Energy is the reduction it would bring about in the overall system cost of meeting a given level and pattern of electricity demand with a defined level of security of supply. In addition to these direct costs and benefits there may be indirect costs and benefits arising from the impact wave power stations and their associated infrastructure make on the environment and man’s activities (Probert and Mitchell, 1981

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  Renewable Energy

  Sustainable Energy Concepts for the Future

  • Roland Wengenmayr, Thomas Bührke, Roland Wengenmayr, Thomas Bührke(Authors)
  • 2011(Publication Date)
  • Wiley-VCH

    (Publisher)

  The deployment of this technology for coastal protection plays in important role in particular in India and in Japan. In the U.S.A. and Europe, it was at first investigated only very hesitantly. In general, most Wave Energy is available on the Western coasts of the big oceans, i.e. on the North and South Pacific coasts of America, on the Atlantic coasts of Europe and (South) Africa, on the Indian Ocean coast of Australia, and on the South Western coast of New Zealand. Precisely for this reason, the coupling of energy extraction with coastal protection is one of the few possibilities of making the use of Wave Energy economically attractive. Large coastal protection facilities however are not without side effects on the ecological system; but there has as yet been no research on this subject.

  The Formation and Propagation of “Gravity Waves “

  The major portion of the energy which is stored in ocean waves is transported by so-called gravity waves (Figure 3 ). They are initiated by the wind and their motion is governed almost entirely by gravitation. Figure 3 also illustrates the forces which activate the waves: short to medium waves are mainly produced by the wind, longer ones by air-pressure differences due to weather fronts or by earthquakes (tsunamis); extremely long waves are due to the tidal forces. The figure also shows the three forces which in general determine the propagation of the waves: surface tension, gravitation, and the Coriolis force. This last force is due to the Earth’s rotation; it is weak and has a noticeable influence on waves only when they are several kilometers long. The surface tension of the water is also a very weak force. It is important only for waves that are shorter than about one centimeter (about half an inch): such waves are deformed by the surface tension. In all other cases, gravity waves predominate. The force of gravity pulls the water in the wave crests down towards the troughs and thus tends to equalize the differences in height.

  Fig.2

  The MIGHTY-WHALE OWC of Japan’s Marine Science and Technology Center (JAMSTEC) was commissioned in 1998. this pilot plant is 30 m (100 ft) wide and floats in water at a depth of 40 m (130 ft); its output power is 110 kW.

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  Renewable Energy

  Sustainable Energy Concepts for the Energy Change

  • Roland Wengenmayr, Thomas Bührke, William D. Brewer(Authors)
  • 2013(Publication Date)
  • Wiley-VCH

    (Publisher)

  Wave Power Plants

  Energy Reserves from the Oceans

  BY KAI-UWE GRAW

  An old dream of humanity is to make use of the almost immeasurable energy of ocean waves. Their destructive power has however up to now not permitted any economically reasonable design to survive for long, although there have been many promising attempts and approaches.

  The reduction in carbon dioxide emissions, which is increasingly urgent and is a major goal of governments and societies, has conferred a new significance on Wave Energy – as on all renewable energy sources. Interest in Wave Energy power plants, which could make appreciable contributions to the world’s energy supply, is steadily growing. The use of Wave Energy for generating electric power has been under investigation for many decades. However, the countless, sometimes extremely naive suggestions for the application of Wave Energy have given this renewable energy source a dubious aftertaste in the public mind. But the long-term commtiment of a few research teams is now leading to a rethinking of this view.

  The ocean waves contain inexhaustible reserves of energy. They are estimated to store around ten million terawatt hours of Wave Energy per year. This makes them, in principle, very attractive as an energy source. However, large waves can deploy a destructive force which makes huge demands on the stability of the wave power plant under load. It is thus particularly interesting to employ wave power plants precisely where the force of large waves must in any case be broken: along coastal protection installations. Conventional breakwaters only reflect or dissipate the Wave Energy without making use of it. Wave power plants, in contrast, extract the energy and convert it into useful electric power. Furthermore, the use of a breakwater as the structure for a power plant reduces the cost of the plant which is integrated into it. Figure 1 shows a new wave power plant in the Spanish harbor Mutriku, whose construction was supported by the EU. With 16 Wells turbines, each delivering 18.5 kW, it can supply 250 households with electrical energy. Wave power plants which convert energy without fulfilling any protective function can even take the form of free-floating installations in the ocean (Figure 2

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