GENERATION Sink or swim by David Flin, freelance energy consultant, UK Despite claims over inadequate funding and a lack of government support, many in the wave and tidal industry would agree that marine renewables are becoming a major new energy option. In this year alone, UK government has made it has examined could host hundreds of Looking to the future, the company plans to firm plans to distribute tens of millions of machines. have 300 MWe installed by 2010. pounds to marine developers, Scotland Environmental impact analyses have But not all developers have adopted propeller has unveiled a European test centre and a confirmed that the technology does not offer type systems. Some interesting new ideas good handful of projects have received cash any serious threat to fish or marine animals. have been developed, including the Stingray injections to stimulate progress. The rotors turn slowly, between 10 - 20 rpm hydroplane device by the Engineering Around the world, engineers are looking to with the risk of impact from rotor blades being Business (EB), based in the north of England, harness tidal currents based on horizontal very small. MCT also says the risk of leakage (see IEE Power Engineer, August/September tidal flows. Indeed, significant tidal currents of noxious substances is insignificant. What’s 2004). exist in many areas where water flows, more, the technology is modular, so small The Stingray Tidal Stream Generator consists speeded up by the configuration of the land, batches of machines could be installed of a hydroplane, which has its attack angle commonly reach 2 m/s. quickly, giving a short period before revenues relative to the approaching water stream start coming in. So what designs are currently under varied by a simple mechanism. The key development? To date, emphasis has been And the cash has also been flowing for MCT, component of the device is the wing like on using wind turbine like devices fixed to the having recently secured a £3,85 m DTI grant hydroplane, attached to a seabed mounted sea bed (see Table1). to demonstrate a 1 MW twin rotor turbine. supporting frame by a moveable arm. The business has also received a grant of The UK has been at the forefront of such ¤1 m from the European Commission to aid But despite taking a lead role in the UK development, mainly as a result of the work commercialisation as well as £960 000 from marine renewables industry, the Engineering of IT Power. In 1994, IT Power built and tested UK government. Business drew a close to development work in a small two bladed 10 kWe prototype, with February of this year. At the time the company support from Scottish Nuclear and NEL, in the MCT also received £3-m investment in a private emphasised that its decision was not based Corran Narrows in Loch Linne, near Fort William equity funding, following initial tests that showed on technical difficulties, but was rather down in Scotland. Following this the business set up rotor coefficient of performance consistently at to “simple economics”. Marine Current Turbines (MCT) to develop a 40 - 45%, and energy capture up to 27% better new version of its “Seaffow” turbine design. than originally expected. As a company statement put it: “For a small private company to stay in business the The company is currently demonstrating its The company’s first phase of development golden rule is to generate cash. There is 300 kW Seaflow experimental prototype at from 1999 to 2003 saw it installing the funding available for future development Lynmouth, UK, and claims the device has first large monopile mounted experimental but not on the scale or basis that will allow delivered 100% availability throughout April 300 kWe single llm diameter rotor system EB to rapidly or profitably make Stingray a of this year (Fig. 1). MCT eventually plans to off Devon in the UK. This uses a dump load commercial reality…we cannot continue to install these turbines in the sea, at places with instead of a connection to the grid, and sustain this project on a non - profit basis.” high tidal current velocities, where flows are only operates with the tide flowing in one predictable. direction. The total cost of this phase came Key results to date include the successful demonstration and recovery of a 500 kWe To economically exploit such turbines, peak in at £3,3-m. generator model. Developments to the spring tidal currents of around 2 - 2,5 m/s are The second phase of development is device’s power cycle had yielded full cycle required at depths between 20 - 35 m. MCT scheduled to finish this year and has involved times of 24 s in a 2 m/s current providing an claims to have identified scores of potentially the first full size twin rotor system, rated average hydraulic power output of 117,5 suitable sites around the UK coastline. at 750 - 1200 kWe being designed, kWe. The Seaffow design consists of twin axial manufactured, installed and tested. The The Engineering Business had also developed flow rotors 15 - 20 m in diameter, each system will be connected to the grid, and cost models that demonstrated the unit driving a generator via a gearbox. The twin function with the tidal flowing in either energy cost could reduce to competitive power units of each system are mounted on direction. Once complete, this phase is levels with increased installed capacity. wing-like extensions either side of a tubular expected to cost £4,5-m, including grid Indeed, the company estimated that a unit steel monopile 3 m in diameter, set into a connection. hole drilled into the seabed from a jack up energy cost of 6,7 p/kWh would be achieved barge. The turbine can be connected to the A third development phase from 2004 - 2005 with 100 MWe of Stingray capacity in place. shore by a marine cable lying on the seabed is seeing the installation of the first array of However, as the company says, its plans are that emerges from the base of the pile. tide turbines interconnected with the second “on hold”, so perhaps as the industry gathers development phase (Fig. 2). Here, between more momentum, we will see fresh activity. According to MCT, submerged 500 - 1000 kWe turbines will eventually be grouped in arrays three to four extra units will give a combined Tidal politics of 10 - 20 machines. However, the company output capacity of 4,5 MWe, and according Gaining recognition for tidal power has believes that many of the potential sites to MCT, this phase is partly self financing. energize - August 2005 - Page 51 GENERATION Device Produced by Description Status Seaflow Marine Current Turbines 500 - 1000 kWe wind Small scale pilot project turbine like device complete. Work on full scale project underway. Tidal turbine Tidal Hydraulic Propeller type turbine Prototypes under Generators development for deployment in Severn estuary. Stingray Engineering Business 5OO kWe hydroplane Development on hold. Rochester Venturi RV Power Company Venturi device to drive Small prototype planned. 2 MWe turbine Polo Prof. Stephen Slater Vertical axis turbine on Idea under development. ring-structure Hammerfest Strom Statoil/ABB 300 kWe wind turbine- Pilot plant under installation like device Fig. 1: Raising Seaflow: the 300 kW prototype is one of many Messina project EU-funded study Vertical-axis propeller Feasibility study underway tidal generators under development Gorlov Helical Northeastern University, Wind turbine-like Small prototypes being tested Turbine Boston device for deep-sea applications been an uphill struggle. In its 1997 - 2000 Tidal fence Blue Energy Vertical-axis turbines Demonstration plant under review of UK renewable energy options, the development UK Department of Trade and Industry (DTI) Table 1: Tidal current development status of key projects relegated tidal current technology to the suitable for development of tidal current Aqua Energy Group is planning a 1 MWe “very long term” category. The technology power generation. wave project in Washington State, USA was expected to be expensive at most sites, so any contribution would be very small. Of these 106 sites, a massive 80% are Japan has a floating wave energy test bed, the Mighty Whale. around the coast of the UK. The best sites are And although further analysis placed between islands or around heavily indented Researchers at the University of Manchester, the potential UK tidal stream resource at coasts where there are strong tidal currents. UK, are developing a wave generator 36 TWh/year, it suggested that only that promises to give an effective power 0,7 TWh might come from tidal streams by Some figures have estimated that if all of the extraction of about 1 kW/m of wave crest for 2010, with 322 MWe of installed capacity. UK’s tidal current sites were developed, these a wave height of 2 m. Project leader, Prof. Indeed, tidal currents did not even appear regions could generate nearly 20 % of the Peter Stansby, says a crucial feature of the in the ranking chart in the consultation paper UK’s electricity requirements. Not bad for a “Manchester Bobber” will be to extract energy produced in 1999, as part of the DTI review technology that, to say the least, has been at so-called low sea states, and hopes to of renewables. a long time coming. eventually produce a device that provides a constant power supply But despite past struggles, the UK House of Current waveprojects Acknowledgement: Commons Select Committee on Science Relative to tidal energy, wave energy is and Technology finally concluded that both This article was published in the June/July 2005 less developed. However, many new wave wave and tidal current technology merited issue of IEE Power Engineer, the members projects are currently underway, including: significantly more attention.