Centre for Renewable Energy Sources - Literature review Example

Centre for Renewable Energy Sources Introduction Since the 1970s, on account of oil crises, attention of many scholars has been focused on the possibility to generate power from natural energy sources. Researches revealed that ocean energy can be converted into electricity by four ways: 1) from the motion of waves; 2) from ocean currents and tides; 3) from the ocean water’s temperature differences; and 4) from the salt and fresh water pressure differences (Tulloch 2010). Waves are considered the most powerful source of energy. The immense energy potential of ocean has been recognized long ago, but the exploitation of waves in the electricity production has started to be investigated only for some last decades (Brooke 2006). Nowadays it is brought out clearly that some methods of ocean wave energy conversion can be successfully used for this purpose, and there are a number of areas in the world where wave energy can be effectively converted into energy, useful and necessary for all humans. Ocean wave’s energy is solar energy in its concentrated form. Cruz (2008) describes the process of wave creation as follows: “the sun produces temperature differences across the globe, causing winds that blow over the ocean surface. These cause ripples, which grow into swells.” (p.1) Ocean waves are distinguished by the highest level of energy density in comparing with other energy sources. Brooke (2006) asserts that the density of wave energy just below ocean surface is five times higher than the density of energy of wind 20m above the sea surface, and 20 to 30 times than the density of solar energy. The theoretical potential of electricity production by using of waves is enormous, according to Tulloch (2010); it can reach up to 80,000 Terawatt hours a year, “almost five times the world’s annual electricity consumption”. Drew et al (2009) mention several other characteristics of ocean waves providing significant advantages of using them for energy production: Relatively low negative environmental impact. It is generally considered that using of waves as the source of renewable energy does not cause CO2 emissions. Waves are much stronger in winter by the nature, so seasonal variability of their energy follows the electricity demand in temperate climates. Waves also can transfer energy on large distances with little losses. Wave power devices can produce electricity up to 90 per cent of the time, while wind and solar power devices only 20–30 per cent (p.888). According to MMS (2006), the common measure of wave power, P, is , where ρ – the density of seawater (1,025 kg/m3), g – acceleration due to gravity (9.8 m/s/s), T – period of wave motion (s), and H – wave height or amplitude (m) (p.2). So, the more are period of motion and height of waves, the more is energy of waves. Figure 1 represents wave power distribution on the Earth. Obviously, Western Europe, North and South America, Australia and South Africa are the most promising regions for the ocean wave energy conversion. Figure 1. Global wave power distribution in kW/m (Source: CRES, 2002, p.9). Literature Review The conversion of the ocean wave energy into the electricity power is not an easy task. CRES (2002) emphasizes several difficult aspects of this process: “Irregularity in wave amplitude, phase and direction; it is difficult to obtain maximum efficiency of a device over the entire range of excitation frequencies; The structural loading in the event of extreme weather conditions, such as hurricanes, may be as high as 100 times the average loading; The coupling of the irregular, slow motion (frequency ~0.1 Hz) of a wave to electrical generators requires typically ~500 times greater frequency” (p.11). Numerous wave energy researches have been undertaken around the world in order to help overcoming these difficulties and make the renewable energy production effective. An overview of several recent research efforts and their results in this area are presented below. Folley and Whittaker (2009) explore differences between offshore and nearshore wave energy resources (typically an offshore is a location with water depth = 50 m and a nearshore is a location with water depth = 10 m). Researchers introduce a new third-generation spectral wave model that provides significantly better measurement of wave farms’ productivity, as well as more exact and reliable comparison between offshore and nearshore wave energy resources. The results of their study disproved the traditional opinion that offshore resource should be considered more effective in comparing with nearshore one. In addition, the exploration of various mechanisms of wave energy reduction on the example of the North Atlantic wave climate modelled in the experiment helped to understand better the differences in the wave energy resource at different water depths. The investigation of the potential of nearshore wave energy resource has been continued in the study of Hemer and Griffin (2010). They explored transformations of nearshore wave energy depending on the propagation of waves across the continental shelf. Using the archives of the USA National Oceanic and Atmospheric Administration (NOAA) Wave Watch III (NWW3) operational wave model, researchers identified three representative deep-water states, which were propagated into the nearshore area by applying the Simulating WAves Nearshore (SWAN) wave model. This allowed accounting for effects of shallow water processes, such as “refraction, shoaling, bottom friction, and sheltering from coasts and islands” (Hemer and Griffin, 2010, p.2). It helped making important conclusions regarding the real potential of nearshore wave energy, in this case for the Southern Australian margin, particularly: “if 10% of the incident nearshore energy in this region, which is an ambitious target when conversion efficiency is considered, were converted to electricity, approximately 130 TW h/yr (one-half of Australia’s total present-day electricity consumption) would be produced.” (Hemer and Griffin, 2010, p.12) Undoubtedly, technology and devices for wave energy conversion should be sophisticated enough to provide high efficiency and operational dependability, yet ensuring economical practicability and expediency. Currently more than 1000 wave energy conversion technologies are patented across the world. Drew et al (2009) suggest classifying all technologies of wave energy conversion within three major categories: attenuators, point absorbers and terminators. In addition, according to modes of operation the technologies can be divided on: the submerged pressure differential devices, oscillating wave surge converters, oscillating water columns, and overtopping devices. Articles of Collier et al. (2008), Henry et al. (2010) and Whittaker et al. (2007) represent a comprehensive, theoretically-based approach to the design and development of the Aquamarine Power Oyster wave energy convertor, which belongs to the oscillating wave surge converters class and is used in a nearshore environment. Collier et al. (2008) generally represent the Oyster concept as a simple Wave Energy Convertor (WEC), which is based on “a bottom hinged flap” (p.1). The underlying principles of the concept allow using oscillating action of waves for capturing energy of waves and converting it into electrical power (see Fig.2). Figure 2. The Oyster Wave Energy Convertor (Source: Collier et al. 2008: 1). Such construction differs considerably, for example, according to Collier et al. (2008), unlike many other systems, “it completely penetrates the water column from the water surface to the sea bed” (p.1). Collier et al. (2008) also point out several positive features of the Oyster WEC, in particular, high capture efficiency, high power to weight ratio, high reliability, design for extreme seas, modular design (p.7). Whittaker et al. (2007) focus more on explanation of hydrodynamic performance of the Oyster WEC, based on the previous research and prototyping. Henry et al. (2010) present results of recent development of the device and the high level design of the next version of the system, Oyster 2. They also emphasise a small difference between the exploitable wave power on the nearshore and offshore regions. Moreover, they assert that such minor difference is completely compensated by the fact that “the harmful extreme events found in the offshore region are filtered in the nearshore” (Henry et al., 2010, p.8). Folley et al. (2007) investigated the effect of water depth on the performance of a small surging wave energy converter (WEC) like the Oyster. The results of their study revealed that “both the surge wave force and power capture of a flap-type WEC increase in shallow water” (p.1264). Moreover the location of WEC devices in the nearshore area provides significant advantages in comparing with offshore locations: lowering cost of the cables bringing power to the shore, lowering losses of the power due to the smaller size of cables, increasing of the device availability, lowering installation and maintenance costs with “operations being completed in shorter weather windows and with less specialised equipment” (Folley et al., 2007, p.1265). Interesting and important results, useful for further investigation, were provided by the study of Beatty et al (2010), which aimed to explore the possibility and technical feasibility of the electrical power integration of a heaving point absorber wave energy converter to the Alaskan island of St. George. As a result of the research the particular design and a specification of the control elements “required for wave/diesel hybridization of small remote electrical grids” (Beatty et al, 2010, p.1204) were developed. The solution was based on the detailed wave resource assessment and thorough planning of operations of the WEC devices. In addition, the performance of the 100kW-capacity WEC station was measured; it showed that practically 9 per cent of the island electrical energy demand can be provided by the solution. This makes a contribution to assumption of good perspectives of marine energy industry development widely discussed currently among governments of many countries. As Aquamarine Power (2010) asserts: “To maintain the lead in an emerging marine energy industry …government must facilitate strong public support for wave and tidal energy in parallel to assisting the most promising technology developers with R&D and project capital grants” (p.6). References Aquamarine Power, 2010. The Danish Wind Industry 1980 - 2010: Lessons for the British Marine Energy Industry. Aquamarine Power. Available from: http://www.aquamarinepower.com/technologies/technical-papers/view/154/the-danish-wind-industry-1980-2010-lessons-for-the-british-marine-energy-industry/ [Accessed 10 November 2010]. Beatty, S.J., Wild, P., and Buckham, B.J., 2010. Integration of a Wave Energy Converter into the Electricity Supply of a Remote Alaskan Island. Renewable Energy, 35, 1203-1213. Brooke, J., 2003. Wave energy conversion. Vol. 6. Oxford: Elsevier. Clement, A., McCullen, P., Falcao, A., Fiorentino, A., Gardner, F., Hammarlund, K., Lemonis, G., Lewis, T., Nielsen, K., Petroncini, S., Pontes, M.-T., Schild, P., Sjostromm, B.-O., Sorensen, H.C., and Thorpe, T., 2002. Wave Energy in Europe: Current Status and Perspectives. Renewable and Sustainable Energy Reviews, 6, 405-431. Collier, D., Whittaker, T., and Crowley, M., 2008. The Construction of Oyster – A Nearshore Surging Wave Energy Converter. Aquamarine Power. Available from: http://www.aquamarinepower.com/technologies/technical-papers/view/134/the-construction-of-oyster-a-nearshore-surging-wave-energy-converter/ [Accessed 10 November 2010]. Cruz J., 2008. Ocean Wave Energy: Current Status and Future Perspectives. Heidelberg: Springer-Verlag. Centre for Renewable Energy Sources (CRES), 2002. Wave Energy Utilization in Europe: Current Status and Perspectives. Available from: http://wave-energy.net/Library/WaveEnergyBrochure.pdf [Accessed 10 November 2010]. Drew, B., Plummer, A.R., Sahinkaya, M.N., 2009. A review of wave energy converter technology. In: Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy. Vol. 223, No. 6, pp. 887-902. Folley, M., Whittaker, T.J.T., 2009. Analysis of the Nearshore Wave Energy Resource. Renewable Energy, 34, 1709-1715. Folley, M., Whittaker, T.J.T., and Henry, A., 2007. The Effect of Water Depth on the Performance of a Small Surging Wave Energy Converter. Ocean Engineering, 34, 1265-1274. Hemer, M. A., and Griffin, D. A., 2010. The Wave Energy Resource along Australia’s Southern Margin. Journal of Renewable and Sustainable Energy, 2 (4), 1-15. Henry, A., Doherty, K., Cameron, L., Whittaker, T., and Doherty, R., 2010. Advances in the Design of the Oyster Wave Energy Converter. Aquamarine Power. Available from: http://www.aquamarinepower.com/technologies/technical-papers/view/133/advances-in-the-design-of-the-oyster-wave-energy-converter/ [Accessed 10 November 2010]. Minerals Management Service (MMS), 2006. Wave Energy Potential on the U.S. Outer Continental Shelf. Technology White Paper. Available from: http://www.ocsenergy.anl.gov/documents/docs/OCS_EIS_WhitePaper_Wave.pdf [Accessed 10 November 2010] Thorpe, T.W., 1999. An Overview of Wave Energy Technologies: Status, Performance and Costs. In: Wave Power - Moving Towards Commercial Viability, IMECHE Seminar, 30 November, 1999, London, UK. Available from: http://www.wave-energy.net/Library/An%20Overview%20of%20Wave%20Energy.pdf [Accessed 10 November 2010]. Tulloch, J., 2010. Ocean Energy Profile: Power in Motion. Allianz.com. Available from: http://knowledge.allianz.com/en/globalissues/energy_co2/renewable_energy/marine_power_ocean_energy_profile.html [Accessed 10 November 2010]. Whittaker, T., Collier, D., Folley, M., Osterried, M., Henry, A., and Crowley, M., 2007. The Development of Oyster - a Shallow Water Surging Wave Energy Converter. In: Proceedings of the 7th European Wave and Tidal Energy Conference, 11-14 September, 2007, Porto, Portugal. Read More