The ongoing push for renewable energies that reduce greenhouse gas emissions has focused the world’s attention on the untapped potential of ocean energy.
This summer marked a significant step forward in the renewable energy sector with the launch of the world’s first commercial ocean energy project in Portugal. While this first project is modest, it is nevertheless significant as it represents the first step in wave and tidal power development – a technology that is not as developed as its renewable peers yet which offers vast potential as a future energy source.
Developments in wave and tidal energy have lagged behind other renewables such as solar or wind because the technology is newer and because it faces several significant technological challenges requiring intensive and expensive R&D activity. Also, the equipment to install the devices needed to capture the sea’s energy is expensive, as is the associated infrastructure.
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This is exacerbated by location as the very force that makes them viable – wave and tidal strength – makes for a harsh operating environment. Companies wanting to install generation devices have also faced competition for vessels to carry out the work from the offshore oil and gas industry.
That said, the technology’s potential is huge. The world’s wave power resource is vast and has been estimated at around 8,000-80,000 TWh a year, which is equivalent to the amount of electricity consumed globally.
The best locations for the technology to be applied are temperate zones (at 30-60 degrees latitude) where strong storms occur but attractive wave climates can also be found within +30 degrees latitude where regular trade winds blow. Here, lower power levels are compensated by smaller wave power variability. Tidal energy potential is also massive, estimated at 3,000 GW but only 3% of this is located in areas suitable for power generation.
Wave energy occurs in the movement of water near the surface of the ocean. Waves are formed by the wind which effectively drags at the water as it blows across. The stronger the wind, and the longer the distance over which it blows, the larger the waves and therefore more energy they carry. As waves reach shallower water nearer the coast they begin to lose momentum and energy through friction with the seabed and eventually break onto the shore. This means that the greatest amount of energy is available in deeper well-exposed waters further offshore.
Tides, caused by the gravitational effects of the sun and moon on oceans, are completely predictable meaning the amount of energy which can be extracted at any given time can be forecast accurately. Tidal streams are fast moving currents created as water flows between areas of differing tidal heights. They are at their strongest in areas where the passage is being funnelled, such as around headlands and between islands.
There are several different types of wave energy device. All take energy out of the motion of the water near the surface and all convert the action of the waves into movements that power generators to produce electricity. The devices include:
Buoys: A floating structure forced to move by waves which can move up and down or side to side. This motion can be used to produce power.
Terminators: A long line of floating structures placed in the sea. As the waves arrive at one side of this line they cause the floats to move against each other, allowing power to be produced.
Overtopping: A floating pool is placed in the sea. As waves arrive they are forced up over a ramp into the pool. The water then flows back into the sea through a turbine to produce power.
Surface following: Seveal frloating structures are hinged together and follow the surface of the sea. The motion of the structures against each other and this causes power to be produced.
Oscillating water columns: A column of water is held in a tube. One end of the tube is open to the sea, the other to the air. The waves make the water column move up and down. This in turn forces air back and forth through an air turbine to produce power.
Although there are many different designs of tidal stream turbine, there are only three main methods of harnessing the flow from tidal streams, and these are:
Cross-flow turbines: A cross-flow turbine is placed in a tidal stream. As water flows past, the turbine turns and produces power.
Axial turbines: An axial turbine is placed in a tidal stream. As water flows past, the turbine turns and produces power – the process works in much the same way as a wind turbine.
Reciprocating hydrofoils: A set of hydrofoils are placed in a tidal stream. By controlling the pitch of the foils the water flow forces them to move up and down repeatedly. This motion is then used to generate power.
Given the lack of a commercial project to date, wave power’s potential received a welcome boost this year with the €9 million Portuguese project – Aguadoura. It was inaugurated on 23 September and is run as a joint venture 77% owned by a group of three promoters comprising asset manager Babcock & Brown, Energias de Portugal and Efacec, while Pelamis Wave Power of Scotland holds the remaining 23%.
The Aguadoura project generates power using three Pelamis Wave Energy Converters which are semi-submerged, articulated structures composed of cylindrical sections linked by hinged joints. Initially, the project will deliver 2.25 MW via an undersea cable to the shore.
The second phase of the project will be to manufacture and install a further 25 devices to bring the installed capacity up to 21 MW. The generators are located approximately three miles off the coast.
Once completed the project is expected to meet the average annual electricity demand of more than 15,000 Portuguese households and save more than 60,000 tonnes a year of carbon dioxide emissions from conventional generating plant.
Pelamis chief executive Phil Metcalf said: “We see this project as an important strategic step to underpin continued commercial growth and technological development.” The project has benefited from Portuguese government legislation and the implementation of a long-term feed-in tariff for electricity generated.
Babcock & Brown will retain a 46.2% share in the project while EDP will retain a 15.4% interest, with an option to acquire a further 15.4%. Efacec, an industrial manufacturer will also retain a 15.4% interest.
This project is part of a broader partnership by Babcock & Brown, EDP, and Efacec – the Ondas de Portugal consortium – which will focus on the development of experimental wave energy projects including developing a Portuguese wave energy cluster.
Only certain areas around the world are suited for wave and tidal projects. The most optimal are in areas where the sea has been in motion for the furthest distance. This means that countries that border the eastern edge of the Atlantic Ocean are particularly well placed to benefit.
This is especially true for the UK and in particular Scotland where the word’s largest tidal stream project was announced in September. Scotland has an estimated 25% of Europe’s tidal resource and around 10% of its wave potential.
ScottishPower Renewables, a unit of Scottish Power owner Iberdrola, itself a major investor in renewable energy sources, plans three sites in Scotland and Ireland with a combined output of 60 MW.
Two of the sites are planned in Scotland, in the Pentland Firth and the Sound of Islay, with the third off the North Antrim coast in Northern Ireland. ScottishPower Renewables expects to submit planning applications in summer 2009.
Each site is being evaluated for with a view to installing between five and 20 tidal turbines. With each turbine having an installed capacity of 1 MW, this could lead to a combined output of 20 MW – or enough energy for over 40,000 homes. Following planning approval, the projects could be operational by 2011.
All three projects are expected to deploy the Là nstrøm tidal turbine developed by Hammerfest Strøm, a company jointly owned by ScottishPower Renewables, StatoilHydro and Hammerfest Energi. The device’s name reflects the Norwegian and Scottish collaboration – being a combination of the Gaelic ‘là n’ meaning ‘full’ and the Norwegian ‘strøm’ meaning ‘tide’.
ScottishPower Renewables believes that the projects represent an important milestone for the marine energy sector in general. “The rapid technological advancement of tidal power has enabled us to progress plans for this project, which has real potential to deliver both significant environmental and economic benefits.”
The company says Là nstrøm is the most advanced tidal turbine in the world following an extensive and successful four-year testing regime in Norway. It will now complete final testing in Scottish conditions, ahead of full deployment of the technology at the tidal farms from 2011.
ScottishPower Renewables has invested in Hammerfest and established a new subsidiary, Hammerfest Strøm UK, to manufacture the devices in Scotland. This company also owns the global rights to manufacture and export the new turbine.
The turbine technology is based on modern sub-sea technology that is currently being used in the Barents Sea, combined with well established hydro power technology. It is a form of “tidal stream” power rather than “tidal barrage” power as there is no need to impound the water.
This has significant environmental advantages by avoiding impacts on sensitive inter-tidal zones in coastal areas. It has been described as an underwater wind turbine, but with much shorter blades which turn more slowly. The units are mounted on the sea bed and aligned to the tidal flow. Each device will generate around 1 MW of output, and in future arrays of multiple devices are anticipated that could generate 50 MW to 100 MW each.
Developments in the last year mean the long-held prospects for ocean power are starting to become a reality. A report from Greentech and the Prometheus Institute released in October 2008 said the sector was poised to grow from less than 10 MW of capacity worldwide today to over 1 GW in just six years, reaching a market worth more than US $500 million annually and dominated by developments in the UK, the US, Canada, Norway, Ireland and Australia.
The report says that in six years, more than US $2 billion will be invested to build commercial ocean wave power farms and another US $2 billion will go towards research and development globally. It also notes that wave power was capturing more attention than tidal power.
Meanwhile, on the other side of the world, New Zealand which has plans to source 90% of its power from renewables by 2025, is considering an array of 200 tidal turbines that would be anchored to the seafloor across the mouth of the 900 km2 Kaipara Harbour near Auckland. Project backer Crest Energy has estimated that the turbines could yield as much as 200 MW, or 3% of the country’s energy demand.
If these projects area able to justify the viability of the technology on a commercial scale, then ocean power could find it has a solid future alongside wind and solar as part of the renewable energy mix.
