WAVE AND TIDAL ENERGY
Population growth, rising demand for energy, annual increases in power costs, political uncertainty, pressure to cut carbon emissions: any one of these issues would make the development of secure supplies of clean energy important; together they make it imperative. That’s why there is strong demand for the power that wave and tidal farms can generate.
Societies across the world are increasingly dependent on the security and reliability of their power supply. In order to meet this demand both now and in the future, energy suppliers are looking for environmentally sound power solutions that provide a sustainable supply. Marine power (both wave and tidal) is predictable and highly abundant, providing an environmentally friendly solution to power demand for generations to come.
Global estimates of exploitable marine energy indicate that it has the capacity to supply 10% of the world’s electricity needs, excluding the power captured to run desalination or hydrogen electrolysis plants and other commercial energy uses.
The UK is recognised as one of the best locations for marine energy in the world. According to the Carbon Trust’s own Future Marine Energy Challenge report (2006), wave and tidal energy could account for up to 20% of UK electricity consumption.
Demand for wave energy will be fuelled by its high density and good predictability. Unlike solar and wind energy, wave energy can be predicted many days in advance primarily due to the combined contributions from distant storms and negligible loss of energy during transit. It is also one of the highest density sources of renewable power.
Similarly, the strong predictability of tidal energy makes it an attractive energy solution: in fact, it is believed to be the most reliable and predictable of all sources of renewable energy.
Strong tidal stream currents are a site-specific, but concentrated, resource. Our planet’s tides are complex and are affected by a number of variables including: tidal patterns; coastal topography; bathymetry and estuarine funnelling. Areas of strong tidal resource, as identified by the Global Energy Network Institute, are found all across the globe including: offshore northeast South America; southwest Central America; eastern Africa; the Gulf of Alaska and the north and east rims of the North Atlantic. The Carbon Trust estimates that the UK tidal resource accounts for approximately half of the total European resource and approximately 10-15% of the known global resource (Carbon Trust Tidal Stream Energy Report 2005), estimating the economically exploitable UK tidal stream resource to be 12TWh/yr.
It is clear that marine resources offer outstanding renewable energy potential. In combination with the current market demand for sustainable energy solutions, there has been considerable growth in the number of marine energy technology developers, in the UK and abroad. The challenge for developers is to deliver reliable, fault tolerant plants capable of surviving in the offshore environment and delivering reliable power to the grid at a competitive price. To be economically viable, the capital and operating costs of wave generation devices must be reduced; and system efficiencies improved in line with the cost reductions achieved in the wind industry.
Aquamarine Power’s (www.aquamarinepower.com) mission is to make marine energy mainstream. It is well on its way to overcoming these challenges, by delivering technology capable of producing clean, reliable and cost effective energy. The result is the design and development of Oyster®, a simple near-shore wave energy converter, and NeptuneTM, a powerful tidal stream device.
The company is a leading developer of wave and tidal marine energy technologies and is currently the only marine energy company developing both wave and tidal power generators simultaneously.
Using a proprietary database of global hydro-dynamic resources and constraints, Aquamarine is also able to identify the best marine energy sites globally. Working in partnership with utilities and renewable energy project developers, Aquamarine develops these sites, delivering full consents and grid connection, for large scale commercial wave and tidal energy projects.
Based in Scotland, Aquamarine’s engineering team includes considerable experience from the offshore wind, marine energy, and oil and gas industries. The in-house site development team’s expertise covers resource modelling, GIS, offshore oil and gas site selection and marine energy consents.
Supporting the in-house team, the company has a long standing research relationship with Queen’s University, Belfast, an acknowledged centre of excellence in Marine Renewables. Its key engineering design partners include Babcock INTEC (formerly Strachan and Henshaw), a leading defence engineering company specialising in providing high integrity design, project management and engineering solutions.
Oyster® is a hydro-electric wave power converter, designed to capture the energy found in amplified surge forces in near-shore waves. Its relative simplicity makes it extremely robust and reliable – vital for any marine device that hopes to succeed in the market. Its other advantages include a high capture factor in the most commonly occurring seas, inherent survivability in extreme storm conditions, minimum moving parts and no electrical components offshore, thereby minimising offshore maintenance.
The principle behind Oyster® is simple. The system consists of a simple steel Oscillating Wave Surge Converter, or pump, fitted with double acting water pistons, deployed near-shore in depths around between 8 and 16m. Each passing wave activates the pump; which delivers high pressure water via a sub-sea pipeline to the shore. Onshore, high-pressure water is converted to electrical power using established and proven, conventional hydro-electric generators.
The peak power generated by each Oyster® unit is between 300 and 600kw, depending on location and configuration. When deployed in multi-MW arrays, several near-shore pumps will feed a single on-shore hydro-electric generator, attached to a single manifold pipeline. With the capacity to build a single on-shore generating plant with an installed capacity of 21MW or higher, the economies of scale that can be achieved with the Oyster® system are clear.
In addition to providing green energy, Oyster® has the capacity to provide fresh water, an increasingly scarce resource in locations across the world. Oyster® achieves this by using the pressurised water to power a reverse osmosis plant to produce desalinated water.
Progressing successfully towards commercialisation, the Oyster® design package has received third-party verification and the full-scale prototype is now fabricated. The prototype will undergo extensive onshore testing, prior sea trials in summer 2009 at the European Marine Energy Centre (EMEC), Orkney, where Aquamarine has secured a test berth and consents. Directional drilling work has recently been completed at the EMEC site in preparation for the prototype deployment. The pipelines will connect Oyster’s hydro-electric plant in the EMEC substation, to the wave device at sea.
NeptuneTM is a reliable and cost-effective tidal energy technology. The project traces its roots back to a partnership between Scottish and Southern Energy and one of the world’s leading engineering companies, and Aquamarine continues to work with Babcock INTEC to deliver the tidal device.
At 2.4MW, NeptuneTM is one of the most powerful tidal stream devices under development and is designed to be competitive with other sources of electricity generation in the UK market. NeptuneTM features bi-directional (flood and ebb) generation, with its design heavily influenced by the use of proven components from the wind turbine industry. The device consists of a pair of horizontal axis tidal turbines, with three blades on each and a nacelle housing the gear box. The modular designed 1.2MW nacelles are mounted on arms and can be attached either to a mooring device or to a single monopile, depending on water depth. The monopile application will be demonstrated by the first full-scale Neptune® prototype in depths of approximately 30m. A NeptuneTM array will involve the clustering of units around a common electrical station, exploiting economies of scale. The retractable arms allow maintenance access from the platform, enabling engineers to service the device in almost all weathers. Further advantages include the need for only relatively small workboats for maintenance, and design for optimum energy capture and efficient installation.
Detailed design of the major components and delivery of the final production designs are now being completed and will undergo third-party verification later this year. Conclusion of contracts for fabrication and installation will follow. Meanwhile, Aquamarine has secured a test berth at the Fall of Warness tidal site at EMEC and is currently working with EMEC to secure the necessary consents. NeptuneTM will undergo sea trials at the EMEC test berth within the next 3 years.
Aquamarine recently invested in Ocean Flow Energy Ltd to secure EvopodTM, a deep water technology for generating electricity from free flowing tidal streams and ocean currents.
The free floating device uses a simple but effective mooring system that allows it to maintain optimum heading into the tidal stream. It can be accessed by boat for first line maintenance and has been developed specifically with the capacity to operate in exposed deep water sites. The device’s patented low motion hull makes it suitable for operation in harsh environments, such as the Pentland Firth.
Ultimately the unique EvopodTM structure could be used to mount Aquamarine’s NeptuneTM nacelles – opening up the whole of the UK’s tidal stream resource for exploitation using Aquamarine’s technologies.
MARINE ENERGY – THE WAY FORWARD
In the current climate, there are strong market fundamentals to support the development of marine energy devices, and with approximately 15% of the global resource, the UK should take the lead in driving this market. At present there are a number of technologies claiming to be best at harnessing the sea’s power. Aquamarine Power is developing two resilient devices simultaneously which are innovative in their simplicity, whilst also able to generate commercial amounts of energy at market competitive rates.