By Anthony T. Jones
Ocean US Management, LLC
Wave energy is growing in popularity and three different methods of producing energy from waves are being tested in an effort to tap into this clean and abundant resource.
The growing demand for energy is fueling a drive for the extraction of sustainable sources. The oceans, which cover 70 per cent of the world, harbour a vast untapped source of renewable energy in the form of waves. According to the World Energy Council, the global energy available from wave energy conversion is 2000 TWh per year. Tapping just 0.2 per cent of this energy would satisfy the current global demand for electricity.
Waves are the most concentrated source of kinetic energy and are a free and sustainable energy resource, created by wind blowing over the ocean’s surface. As the distance becomes greater, the waves become higher and longer. The energy is stored in this way until it reaches the shallows or beaches where the energy is released, sometimes with disastrous effects. New methods of utilizing this energy are now being explored and tested.
Mid to high latitude locations offer the best wave resource. The Pacific Ocean is the most consistent ocean for wave energy and offers an abundant source of power. Almost all of the wave energy is concentrated in the upper few meters of the ocean. This energy from the wave front is proportional to the square of the wave height. [P=0.98 H2*T].
The ability to rapidly assess the resource potential is greatly enhanced by the use of satellite-derived wave measures and global ocean weather databases. Local geographic variations and physical site characteristics, including distance to end-users, are key criteria in developing economically viable projects. A main component in project costs is the transmission and connection of the energy to regional grids – sometimes out weighting the cost of construction of the wave energy conversion technology.
The technology for potential mainstream power generation is available today. Over 400 patents on wave energy devices have been filed. Although there are various designs, there are three basic ways of converting the ocean’s kinetic energy.
The first method is a tapered channel which focuses the wave energy into an elevated reservoir. A turbine is spun when the water returns to sea level. These systems can be located both onshore and offshore. A onshore example is Tapchan, which operated in Norway from 1985 to 1988. An offshore example is the floating artificial beach called, ‘Merrimack’, created by US Myriad Technologies.
Figure 1. Developments in wave technology could enable us to harness 2000 Twh/yr according to the World Energy Council.
A second method of converting the wave energy is capturing the vertical motion of a float. Various ‘heaving buoy’ mechanisms have been advanced to capture the motion of the sea including hydraulic pumps, springs and piezoelectric polymers. An example is Sea Power & Associate’s wave rider design that utilizes a special hydraulic pump to create hydraulic pressure as the buoy is accelerated by the passing wave.
The third method utilizes an oscillating water column (OWC). Water rising in a cylinder forces air out through a simple turbine. The retreating water forces air back into the chamber again, passing through a turbine. Pioneered by the company WaveGen, their system known as Land-Installed Marine Power Energy Transformer or Limpet, uses a highly-reliable simple air turbine and is designed in such a way that all electrical components are on land.
Limpet is located on the Isle of Islay in Scotland, UK, and is currently delivering 500 MW of power to the national grid. The company evolved from a government-supported laboratory into a private company and has recently secured a 20-year power purchase contract with Scottish Power.
Figure 2. Regional forecast of installed wave energy capacity
Australian oceanographer, Tom Denniss, has taken the concept of the OWC one step further by focusing the on-coming waves with a parabolic wave reflector to concentrate and amplify the wave’s energy. His company, Energetech (Australia) has tested this system at 1:25 scale at the University of South Wales.
The testing demonstrated a wave height enhancement of two to four fold. The company estimates that parabolic bays 40 meters by 20 meters would generate between 250 kW to 1 MW per day. A demonstration facility is underway in Port Kembla. The company is in discussions with independent power producers in Hawaii and the Pacific Northwest for future projects.
Several promising technologies in wave power are in the feasibility phase. Some governments have been very supportive of efforts to develop renewable ocean-based technologies. For example, the Danish government is supporting the development of 40 new concepts in wave energy conversion. As governments change policies directed toward inclusion of renewable energy systems, technologies to harness the oceans processes with their tremendous potential will need to be carefully considered.
The economic viability of wave energy is the leading uncertainty in securing capital for development of concepts into commercial ventures. The cost of harnessing wave energy has declined dramatically over the past decade. Now, most developers are targeting
The main reason for the efficiencies is that redesigns have incorporated technology breakthroughs and utilize the greater computational facilities available today to design hydrodynamically efficient systems. By incorporating experience gained from earlier prototypes of wave energy devices and experiences gained as offshore oil and gas prospects move into deeper water, designers and engineers can build more efficient, reliable systems for the offshore wave conditions.
Tom Thorpe, consultant to the European Thematic Network on Wave Energy stated that if the development programmes of companies engaged in this activity go forward, then the global contribution of wave power is over 2 TWh/yr. He estimates that this represents over $200 billion in planned investment. While his estimate may be overly optimistic, any forecast toward commercialization must consider the political attitudes and energy industries attitudes.
Oceans of energy await harnessing. Various companies, which have developed their own technology, are in the process of proving their technology at sea. Several demonstration projects are planned over the next several months including those by Sea Power & Associates (California), US Myriad Technologies (New Jersey), Ocean Power Technology (New Jersey), S.D.E. (Israel), and Ocean Power Delivery (UK), among others.
The European market will most likely dominate wave power over the next decade. The US energy market is turning toward hydrocarbons for their next generation of power plants. Other markets lack the level of investment and long-term support necessary to undertake the risk of wave energy conversion. The European market has access to long-term financial support, abundant prospective purchasers, an extensive grid network and is aware of the increasing requirements for green energy to lead the way in developing this sector.
Figure 3. The cost of harnessing wave energy has declined dramatically over the past decade
Recent forecasts report installed wave energy capacity will reach at least 50 MW by the end of the decade. Shoreline-based technologies will account for about 40 per cent of this projection. As advances in offshore oil and gas technology in mooring and cabling gain access to the wave energy sector, offshore wave devices will gain momentum by 2010.
Along the Pacific coast of Canada, the British Columbia utility, BC Hydro, is soliciting proposals for the development of wave energy demonstration projects (4 MW capacity) and expects to reach a goal of 100 MW capacity from wave energy conversion systems in the near future. Concerns about extraction efficiency, cost of energy, and energy pricing will be addressed over the course of the demonstration project.
Because wave energy is a highly reliable, predictable source of energy, systems could be designed to enhance grid stability and maintain grid voltage. Imagine a series of wave buoy farms off the Pacific coast from British Columbia to Baja California, all connected to the grid providing voltage control along the West Coast corridor from BC Hydro to Washington State and the Bonneville Power Authority and hooked to California’s Pacific Gas and Electric and Southern California Edison’s systems.
The commitment of countries to take steps to reduce emissions of carbon dioxide and other greenhouse gases will spur commercialization of these technologies. Renewable energy systems from the ocean exist and will be developed further as energy demand escalates.