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Offshore Wave Energy

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  1. Offshore Wave Energy Lars Espevik

  2. The policy • To utilize the energy in waves to produce electricity • Why offshore? • The waves on the open sea have great energy potential • Negligible environmental impacts

  3. Problems addressed • Increase the amount of electricity that originates from renewables • Minimize the use of fossil fuels in the long run • Address climate change problems • Make wave energy economically feasible

  4. Conclusions • Wave energy has great potential • Offshore wave energy is just in its starting phase • Many scientific and economic obstacles remain • The problem of transportation and storing

  5. Topics • History of wave energy • What causes waves? • Wave energy converters • Offshore devices • Advantages/disadvantages • Legal/economic incentives • The future of wave energy


  6. History of wave energy • Before 1973 • First ideas patented in 1799 • Between 1855 and 1973 there were 340 patents • Several configurations of wave energy converters were designed and tested at model scale and some have been operated at sea

  7. History • After 1973 • In Europe, intensive research and development study of wave energy conversion began after the dramatic increase in oil prices in 1973 • Several research programs with government and private support started mainly in the UK, Portugal, Ireland, Norway, Sweden and Denmark

  8. History

  9. History • In the early 1980s the UK government put a stop to the funding of wave energy projects • The increased focus on climate change from the mid 1990s led to increased interest in renewables • Also, the recent increases in the oil price has improved the attractiveness of emerging renewable technologies such as wave energy

  10. History • International conferences in wave energy were held in Edinburgh, UK, 1993, Lisbon, Portugal, 1995, Patras, Greece, 1998 and Aalborg, Denmark, 2000 • At present there are more than 1,000 patents held worldwide related to wave energy • Some commercial plants have been deployed • At present the world-installed capacity is about 2 MW

  11. What causes waves? • The wave energy resource is a concentrated form of solar energy • Winds generated by the differential heating of the earth pass over open bodies of water • The wind pushes surface water particles along with it, setting up a rolling motion in the water and moving the water particles in a vertical, circular path

  12. What causes waves?

  13. Wave energy densities • The power in a wave is proportional to the square of the amplitude and to the period of the motion • Large amplitude (~2 m), long period (~7-10 s) waves have energy fluxes commonly exceeding 40-50 kW/m width of oncoming wave • Wave energy is unevenly distributed over the globe

  14. Wave energy densities around the globe Numbers in kW/m

  15. Wave climate in Europe The wave climate along the western coast of Europe is characterized by particularly high energy. The UK has over half the wave energy potential in Europe, up to 75 kW/m off Ireland and Scotland Wave climate in the US The West Coast is the most promising area with wave energy densities in the 25 – 40 kW/m range Wave energy densities around the globe

  16. Wave energy converters • Four different types of WECs: • Oscillating water columns • Overtopping devices • Point absorbers • Surging devices

  17. The oscillating water column Partly submerged structure with an opening to the sea below the water line Waves cause the water column to rise and fall, which alternately compresses and depressurizes the air column Wave energy converters • This air flows through a turbine which drives an electric generator

  18. Wave energy converters • Point absorbers • They provide a heave motion that is converted by mechanical/ hydraulic systems in linear or rotational motion for driving electrical generators

  19. Surging devices Surging devices exploit the horizontal particle velocity in a wave to drive a deflector or to generate pumping effect of a flexible bag facing the wave front Wave energy converters

  20. Placement of wave energy converters • Three locations • Shore • Near shore • Offshore

  21. Placement of WECs • Shore/Near shore vs. offshore • The potential energy • The power available in the waves is much greater offshore • Nearer the coastline the average energy intensity of a wave decreases due to interaction with the seabed

  22. Placement of WECs • Other factors • Engineering challenges • Construction costs • Maintenance and/or installation costs • Transmission costs and losses • Environmental impacts • The scale of electricity production

  23. Offshore devices • The Archimedes Wave Swing • An underwater buoy of which the upper part (floater) moves up and down in the wave while the lower part stays in position • The floater is pushed down under a wave top and moves up under a wave trough

  24. Offshore devices

  25. Offshore devices • The Archimedes Wave Swing • The interior of the system is pressurized with air and serves as an air spring • The mechanical power is converted into electrical power by means of a Power Take Off system (PTO) • The PTO consists of a linear electrical generator and a nitrogen filled damping cylinder • Problems installing the 2 MW system off the coast of Portugal

  26. The Floating Wave Power Vessel Consists of a floating basin supported by ballast tanks in four sections A patented anchor system allows the orientation of the vessel to the most energetic wave direction A 1.5 mW vessel is planned to be deployed at 50–80 m depth 500 m offshore Shetland Offshore devices

  27. The Wave dragon Is an overtopping device, which elevates ocean waves to a reservoir above sea level Water is let out through a number of turbines and in this way transformed into electricity The prototype is deployed in Nissum Bredning, an inlet in the northern part of Denmark Offshore devices

  28. Offshore devices • The McCabe Wave Pump

  29. Offshore devices • The McCabe Wave Pump • The device consists of three rectangular steel pontoons, which are hinged together across their beam

  30. Offshore devices • The McCabe Wave Pump • The MWP was primarily designed to produce potable water although it can also be used to produce electricity • A 40 m long prototype was deployed in 1996 off the coast of Kilbaha, County Clare, Ireland

  31. The Mighty Whale Is an OWC based device for offshore operation A 120 kW prototype with 3 OWCs in a row has been operating since 1998 1.5 km off Nansei Town, Japan at 40 m depth Offshore devices

  32. Offshore devices • PowerBuoy • Developed in the US by Ocean Power Technologies • It is awave generation system that uses a buoy to capture and convert wave energy into a controlled mechanical force which drives an electrical generator

  33. Offshore devices

  34. Offshore devices • PowerBuoy • The PowerBuoy is enhanced with sensors, which continuously monitor the performance of the various subsystems and surrounding ocean environment. In the event of very large oncoming waves, the system automatically disconnects • In 2002 the company received funding of $ 4,300,000 from the US Navy’s Office of Naval Research for the first major phase of a wave power project in Hawaii

  35. Offshore devices • The Pelamis • Is a semi-submerged structure composed of cylindrical sections linked by hinged joints

  36. Offshore devices • The Pelamis • The wave induced motion of these joints is resisted by hydraulic rams which pump high pressure oil through hydraulic motors via smoothing accumulators • The hydraulic motors drive electrical generators to produce electricity

  37. Offshore devices • The Pelamis • Several devices can be connected together and linked to shore through a single seabed cable

  38. Offshore devices • The Pelamis • A typical 30MW installation would occupy a square kilometre of ocean and provide sufficient electricity for 20,000 homes • Ocean Power Delivery has won a bid for a 750kW project off Islay, Scotland and has recently signed a memorandum of understanding with BC Hydro to develop a 2 MW project off the coast of Vancouver Island, Canada

  39. Advantages • Advantages of offshore wave energy • Sea waves have high energy densities, the highest among renewable energy sources • Wave energy is generally considered to provide a clean source of renewable energy with limited negative environmental impacts • It could become a significant source of energy not involving CO2 emissions

  40. Advantages • The natural seasonal variability of wave energy follows the electricity demand in temperate climates • Negligible demand on land use • Could secure energy supplies in remote regions • Large-scale implementation of wave power technologies will stimulate declining industries, e.g. shipbuilding

  41. Disadvantages • Disadvantages of offshore wave energy • The main wave energy barriers result from the energy carrier itself: The sea • The peak-to-average load ratio in the sea is very high and difficult to predict • The structural loading in the event of extreme weather conditions, such as hurricanes, may be as high as 100 times the average loading

  42. Disadvantages • High construction costs induce high power generation costs, thus making the technology uncompetitive  • The incidence of wave power at deep ocean sites is three to eight times the wave power at adjacent coastal sites, but the cost of electricity transmission from deep ocean sites is often prohibitively high

  43. Environmental impacts • Offshore wave energy devices may be a potential navigation hazard to ships • Near shore devices will have a visual impact • Wave energy devices could have an effect on some forms of recreation • Impacts on the marine environment

  44. Legal incentives • Public Utility Regulatory Policy Act (PURPA) • State goals for renewable energy • Renewable Portfolio Standards (RPS) • System Benefit Charges

  45. Government funding • Research and development efforts are being sponsored by government agencies in Europe and Scandinavia • In the US there is little research due to lack of funding. The Navy, through its Office of Naval Research SBIR program, has provided some research funds. Generally, the funding level is not adequate for demonstration projects

  46. The future • Need of technology improvements • Wave energy conversion technologies have significantly advanced during recent years, especially in Europe • Most devices are still in the prototype-phase • The survivability/reliability of devices for offshore operation has still to be demonstrated • Combination of offshore wind and wave energy devices?

  47. The future?