Tidal stream generator
Several prototypes have shown promise, with many companies making bold claims, some of which are yet to be independently verified, but they have not operated commercially for extended periods to establish performance and rates of return on investments.
[16] The strong currents pose challenges to the design: the blades of the 2006 and 2007 prototypes broke and new reinforced turbines were installed in September 2008.
[17][18] Following the Seaflow trial, a full-size prototype called SeaGen was installed by Marine Current Turbines in Strangford Lough in Northern Ireland in April 2008.
The turbine began to generate at full power of just over 1.2 MW in December 2008,[19] is reported to have fed 150 kW into the grid for the first time on July 17, 2008, and has now contributed more than a gigawatt hour to consumers in Northern Ireland.
[22] A prototype semi-submerged floating tethered tidal turbine called Evopod has been tested since June 2008[23] in Strangford Lough, Northern Ireland at 1/10 scale.
Neptune Renewable Energy's Proteus project[31] employs a shrouded vertical axis turbine that can be used to form an array in mainly estuarine conditions.
ORPC has developed TGU designs that can be used for generating power from river, tidal, and deep water ocean currents.
Tidal Energy delivered their shrouded turbine in northern Australia, where some of the fastest recorded flows (11 m/s, 21 knots) are found.
Another larger 5 meter diameter turbine, capable of 800 kW in 4 m/s of flow, was planned as a tidal-powered desalination showcase near Brisbane Australia.
[35] During 2003 a 150 kW oscillating hydroplane device, the Stingray tidal stream generator, was tested off the Scottish coast.
[40] The bioSTREAM tidal power conversion system uses the biomimicry of swimming species, such as sharks, tuna, and mackerel, using their highly efficient Thunniform mode propulsion.
Each kite is equipped with a gearless turbine to generate which is transmitted by the attachment cable to a transformer and then to the electricity grid.
[46] There are many individuals and companies developing tidal energy converters across the world, although few have progressed beyond the concept on initial testing stage.
Its grid connected tidal test site is located at the Fall of Warness, off the island of Eday, in a narrow channel which concentrates the tide as it flows between the Atlantic Ocean and North Sea.
[51] In 2010, The Crown Estate awarded an agreement for lease to MeyGen Limited, granting the option to develop a tidal stream project of up to 398 MW at an offshore site between Scotland's northernmost coast and the island of Stroma.
[55][12] SIMEC Atlantis Energy, now SAE, was awarded Contracts for Difference totalling 59 MW for the next phases, to be built by 2029.
This would not only supply the island's needs but also leave a considerable surplus for export,[64] using a France-Alderney-Britain cable (FAB Link) which was expected to go online by 2020.
[67] The array was expected to be fully operational by 2015, however the project was shelved in 2016 after Marine Current Turbines was acquired by SIMEC Atlantis Energy.
[68] In 2015, Welsh companies Tidal Energy Ltd (TEL) and Eco2 aimed to deploy a commercial scale demonstration project, with nine turbines at St Davids Head.
[70] In March 2014, the Federal Energy Regulatory Committee (FERC) approved a pilot license for Snohomish County PUD to install two OpenHydro tidal turbines in Admiralty Inlet, WA.
The tidal turbines will use are designed to be placed directly into the seafloor at a depth of roughly 200 feet, so that there will be no effect on commercial navigation overhead.
The license granted by the FERC also includes plans to protect fish, wildlife, as well as cultural and aesthetic resources, in addition to navigation.
[74] ScottishPower Renewables planned to deploy ten 1MW HS1000 devices designed by Hammerfest Strom in the Sound of Islay in 2013.
In these situations it is the frontal area of the duct, rather than the turbine, which is used in calculating the power coefficient and therefore the Betz limit still applies to the device as a whole.
For example, the maximum physical possible energy extraction from a strait connecting two large basins is given to within 10% by:[77][78] where As with wind power, selection of location is critical for the tidal turbine.
Tidal stream systems need to be located in areas with fast currents where natural flows are concentrated between obstructions, for example at the entrances to bays and rivers, around rocky points, headlands, or between islands or other land masses.
As with all offshore renewable energies, there is also a concern about how the creation of EMF and acoustic outputs may affect marine organisms.
Tidal energy removal can also cause environmental concerns such as degrading farfield water quality and disrupting sediment processes.
Depending on the size of the project, these effects can range from small traces of sediment build up near the tidal device to severely affecting nearshore ecosystems and processes.
[90] One study of the Roosevelt Island Tidal Energy (RITE, Verdant Power) project in the East River (New York City), used 24 split beam hydroacoustic sensors (scientific echosounder) to detect and track the movement of fish both upstream and downstream of each of six turbines.
