Select Committee on Science and Technology Appendices to the Minutes of Evidence


Memorandum submitted by the International Energy Agency

  The International Energy Agency is presently launching a new Implementing Agreement on Ocean Energy focused initially on Wave Energy and Marine Currents. Denmark, the European Union, Portugal and the UK form the Interim Executive Committee. Other countries have shown interest, namely Ireland, Japan, Norway, Netherlands, USA, Mexico, India. The IA activities will be closely co-ordinated with those of the European Thematic Wave Energy Network. The Outline on Ocean Energy Technologies (Annex), prepared to serve as a basis for the establishment of this new IA provides a summary of the status of these technologies.

  The initiative to start up this new IA with activities on wave and tidal stream energy is the result of the importance of these renewable energy resources, and the R&D and demonstration activities, with the start of the commercial exploitation of wave energy. Important achievements have been made in Europe. Two 0.5 MW wave energy power plants of the Oscillating Water Column (OWC) type have been built in the Azores, Portugal, and in Scotland, UK, the latter being running commercially. In addition a 2MW prototype of a Dutch offshore device is under construction, its deployment off Portugal is planned for summer 2001. In Japan, India and China prototypes of OWC and other device types have been tested during the last decade. In China and Australia, OWCs rated 100 kW and 600 kW respectively are under construction, the latter being a commercial initiative. For tidal streams, two prototypes rated 300 kW and 130 kW are planned to be deployed in 2001 in the south-west of England (Bristol Channel) and in the Straight of Messina, Italy. In USA, a few companies are being funded by the Government to develop marine current devices.



  Several types of ocean energy sources with different origins exist. The most developed conversion systems concern tidal energy, which results from the gravitational fields of the moon and the sun; thermal energy (Ocean Thermal Energy Conversion or OTEC), resulting directly from solar radiation; marine currents, caused by thermal differences in addition to tidal effects; and ocean waves, generated by the action of the winds blowing over the ocean surface. Harnessing the offshore wind energy can be considered an ocean energy technology.

  An outline of the resource availablity, the state-of-the-art of the technology, existing or demonstration plants, economics and environmental impacts for tidal, marine currents and wave energy resource follows. This is intended to serve as a basis to an Implementing Agreement on Ocean Energy that is proposed herein.


  Significant development of tidal energy technology occurred during the past 30 years, particularly in France, Canada, the USSR and China. A small number of commercial power plants are in operation.


  The tides are generated by the rotation of the earth within the gravitational fields of the moon and the sun. The relative motions of these bodies cause the surface of the oceans to be raised and lowered periodically. Tidal energy is predictable in both its timing and magnitude.

  The locations where tidal power could be developed economically are relatively few, because a mean tidal range of five metres or more is needed for the cost of electricity to be competitive with conventional power plants. Additional requirements are a large reservoir, and a short and shallow dam closure.


  A barrage constructed across an estuary is equipped with a series of sluice gates and a bank of low head axial turbines. The most common construction method involves the use of caissons. Tidal energy technology can be considered largely mature with a 240 MW commercial unit operating successfully since 1966 in France at La Rance. Smaller units have been constructed in other countries namely Canada (Bay of Fundy, 17.8MW, 30 GWh/yr, 1984), USSR (Kislogubskaya near Murmansk, 0.4 MW, 1968), and China (Jiangxia, 3.2 MW, 11 GWh/yr, 1980) and others (CEC, 1992).

  To widen the range of suitable sites a new approach that uses an impoundment structure that sits nearshore on the ocean floor has been patented by a US company. A contract with Alaska authorities for the construction of a 2 MW tidal plant of this type is being prepared.

Economics and Environmental Impacts

  Tidal power incurs relatively high capital costs, and construction times can be several years for larger projects. The operation is intermittent with load factor 22-35 per cent. Plant lifetime can be very long (120 years for the barrage structure and 40 years for the equipment). The high capital costs and long construction time have deterred the construction of large tidal schemes.

  Tidal barrages can cause significant modifications to the basin ecosystem. However they can also bring benefits like flood protection, road crossing, marina and increased tourism.


  Kinetic energy from the sea can be harnessed using techniques similar in principle to those for extracting energy from the wind, by using submarine converters similar to "underwater windmills", but this option is still relatively undeveloped. A number of studies have been completed on the energy potential of marine currents but there have been few on the engineering requirements for utilisation of this resource. Countries where theoretical studies and experimental projects took place are UK, Canada, Japan, Russia, Australia and China in addition to the European Union.

  The start up of the exploitation of the marine currents energy can make use of conventional engineering components and systems but development is required to achieve reliability and durability of the equipment at low operational and maintenance costs. Further research will be necessary to develop more efficient converters at lower electrical energy unit costs.


  Studies to assess the marine currents resource have been recently carried out in UK (DTI, 1993), European Union (CEC, 1996b) and in far-eastern countries (CEC, 1998).

  In Europe this resource is of special interest for UK, Ireland, Greece, France and Italy. In this area 106 suitable locations were identified and it was estimated that, using present day technology, these sites could supply 48TWh/yr to the European electrical grid network. In China it has been estimated that 7,000 MW of tidal current energy are available. Locations with high potential have also been identified in the Philippines, Japan, Australia, Northern Africa and South America. The predictability of marine currents and the high load factor (20-60 per cent) are important positive factors for its utilisation.

  There remains much uncertainty with regard to the detailed characteristics of this marine resource. The available marine current data are limited and inconsistent. Even where velocities were measured, these were single point measurements close to the surface whereas the converters are to be deployed in deeper water (at least 20m). The development of efficient 3D numerical flow models in addition to long-term data collection will enable to produce a comprehensive accurate assessment of this resource.


  The technique that has been mostly considered for the exploitation of marine currents is to use a turbine rotor, set normal to the flow direction, that is mounted on the seabed or suspended from a floating platform. The greatest technical problems are likely to arise from the need for adequate operational life and low maintenance costs from machinery operating in a hard environment, although the offshore industry has solved similar problems. First generation systems will be based on the use of conventional engineering components and systems in order to achieve reasonable reliability at low costs. A medium-sized turbine, of 10-15 m diameter and 200-700 kW rated power, deployed in as shallow water as possible (ie 20-30 m water depth), is likely to be the most economic overall solution for the first generation machines (CEC, 1996b). Second generation systems can follow from this by introducing specialised components, such as low speed multi-pole electrical generators, hydraulic transmission systems, etc. Novel concepts to be developed within R&D programmes will be the third generation systems.

  Design, construction and installation of turbines in UK and Italy, that will supply electrical energy to the national grids, are being funded by the European Commission (the turbines will be commissioned in 2000 in UK (300 kW), and 2001 in the Strait of Messina, Italy, 100 kW rated power). These projects are being led by SME's. The construction of a 75 kW device is planned for China with European collaboration.


  Estimates of unit costs of electrical energy vary between 0.05 and 0.15 ECU/kWh depending on the studies. The assessment described in CEC (1996b) has estimated that costs of less than 0.10 ECU/kWh would be achievable with first generation machines in a good current regime with reasonable load factor.

Environmental Impacts

  The environmental impact of submerged marine current turbines will be minimal; the main conflicts are expected to be with shipping, navigation and fishing. Modification of sediment transport as a consequence of current energy extraction may occur.


  The conversion of ocean wave energy requires new technology to an extent larger than for most of other ocean energy sources. Considerable research on wave energy conversion began only after 1973's oil crisis, and took place in UK, Japan, Norway, Sweden and USA, a few years later in Denmark, Ireland and Portugal, and, in the 1980s, in India and China. In the 1990s activity in this subject started in Mexico, Australia and Netherlands. Based on various energy-extracting methods a wide range of systems was proposed. Only a few reached the demonstration stage.


  Wave energy can be considered a concentrated form of solar energy. Winds are generated by the differential heating of the earth, and, as a result of their blowing over large areas of water, part of their energy is converted into waves. Just below the oceans surface wave energy flux, in time average, is typically five times denser than the wind energy flux 20 metres above the surface, and 10 to 30 times denser than the solar energy. The best wave climates, with annual average power levels between 20 and 70 kW/m or higher, are found in the temperate zones (30 to 60 degrees latitude) where strong storms occur. However, attractive wave climates are still found within ±30 degrees latitude where regular trade winds blow, the lower power level being here compensated by the smaller wave power variability.

  The global wave power potential was estimated to be 1 TW, which is the same order of magnitude of the world consumption of electrical energy. Resource assessments have been undertaken at national level and, more recently, at the European level (CEC, 1996a). A global assessment based on visual observations (Quayle and Changery, 1982) must also be referred. Based on the European Wave Energy Atlas, the total annual deep water resource along the Atlantic and Mediterranean coasts of Europe was estimated to amount to about 320 GW. The highest annual wave power level off the European coasts is 75 kW/m off Ireland and Scotland and it decreases gradually to about 30 kW/m off northern Norway and off the southern Atlantic Madeira and Canary archipelagos.

  Nearshore and mainly at the shoreline the wave power level is in general smaller than offshore because of wave breaking in shallow waters. Other phenomena as refraction, and difraction in indented coastlines, can cause significant resource variations within lengths of 1 km or much less, especially at the shoreline.

  The conversion of the available resource could supply the whole or a substantial part of the electrical energy demand in several countries as eg Ireland and Portugal, in Europe, whereas in remote areas the conversion of a small fraction of the available resource could meet the whole electrical energy demand.


  The large number of different concepts under investigation at present in various parts of the world suggests that the best technology has not yet been indentified. Prototypes of just a few types have been tested in the sea, the best known of which are the oscillating water column (OWC) and the convergent channel (Tapchan).

  The OWC device comprises a partly submerged concrete or steel structure, open below the water surface, inside which air is trapped above the water free surface. The oscillation of the internal free surface produced by the incident waves makes the air to flow through a turbine that drives an electric generator. The self-rectifying axial-flow Wells turbine had been used in almost all the prototypes. Eight prototypes have been tested since 1985 in Norway, Japan, UK, India, China and Portugal, the rated power ranging between 20 and 500 kW. Most of the devices are located on the shoreline where maintenance and installation are easier and moorings and underwater electricity transmission are avoided. In two cases (India and Japan) bottom-fixed nearshore devices have been located just outside or incorporated in a protecting breakwater (a way of building the plant at marginal costs). A floating OWC device was constructed in Japan with the double purpose of producing electrical energy and providing shelter.

  The Tapchan comprises a gradually narrowing channel with wall heights above mean water level. As the waves propagate down the channel, the wave height is amplified until the wave crests spill over the walls to a reservior which provides a stable water supply to a conventional low head turbine. A demonstration Tapchan device with rated output of 350kW operated from 1985 to the mid-1990s in Norway. This is considered a relatively mature technology.

  A shoreline or nearshore advice ("Pendulor"), based on a pendulum or oscillating flap acted upon directly by the waves, has been under development for a number of years in Japan and more recently in China (this included sea tests of models). The construction in China of a prototype rated 30kW is being planned.

  Although some floating devices have shown good prospects to be competitive with conventional electricity production, no offshore device has yet been demonstrated at full scale. The proposed floating devices are intended for electricity production and, in some cases, for fresh water supply. These devices, that will exploit the more powerful wave regimes available in deep water (typically more than 40 m water depth) require flexible moorings and electrical transmission cables. Reduced models of some have been temporarily deployed in the sea. The contracts for construction of two floating systems are underway in Scotland and Australia. The development and construction of a wave power vessel has been contracted with the Scottish authorities. A prototype of a floating wave pump to supply fresh water or electrical energy has recently undergone sea tests in Ireland.


  It is difficult to realistically estimate the unit costs of electrical energy produced from the waves since the few existing schemes have been prototypes with the additional costs incurred by such a stage of development. However the estimated costs have shown a steady decrease with time, despite the little financial support received in recent years. It should be noted that the cost of energy produced is a function of local wave climate and, in the case shoreline devices, is site specific.

  It appears that several devices have already the potential to provide cheaper electrical energy for small islands and remote coastal communities that depend on expensive Diesel generation.

Environmental Impacts

  Wave power generation is generally considered environmentally benign. For shoreline power plants, the main negative impacts are visual intrusion and noise from air turbines. Nearshore and offshore plants may constitute obstacles to coastal marine traffic and, when deployed in large numbers, may promote modifications to coastal dynamics. Other impacts, namely on the ecosystems, on fishing and on recreation and tourism may occur. Most of these burdens can be minimised and, in some cases, eliminated.

  A detailed environmental cause-and-effect study of any intended deployment should be required. A strategy for the assessment and quantification of environmental impacts needs to be developed.


  Commission of the European Communities, DGXVII (1992), The Potential for Tidal Energy Community within the European Union, prepared by ETSU and CCE.

  Commisson of the European Communities, DGXII (1996a), Atlas of Wave Energy Resource in Europe, Final Report. JOULE Contact No JOU2-CT93-0312.

  Commission of the European Communities, DGXII (1996b), Wave Energy Project Results: The Exploitation of Tidal Marine Currents, Report EUR16683EN.

  Commission of the European Communities, DGXVII (1998), Promotion of New Energy Sources in the Zhejiang Province, China, Final Report. Program SYNERGY Contract No 4.1041/D/97-09.

  Department of Trade and Industry, UK (1993), Tidal Stream Energy Review, Report No ETSU T/05/00155/REP.

  Quayle, R G and M J Changery (1982), "Estimates of coastal deepwater wave energy potential for the world", Proc. Oceans '81 Conf, Boston, Vol 1, p 903-907

15 March 2001

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