![Evopod in Strangford Lough 2008](https://upload.wikimedia.org/wikipedia/commons/a/af/Evopod_in_Strangford_Lough_2008.jpg)
A tidal stream generator, often referred to as a tidal energy converter (TEC), is a machine that extracts
energy
In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat a ...
from moving masses of water, in particular
tides
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another.
Tide tables can ...
, although the term is often used in reference to machines designed to extract energy from run of river or tidal estuarine sites. Certain types of these machines function very much like underwater
wind turbine
A wind turbine is a device that converts the kinetic energy of wind into electrical energy. Hundreds of thousands of large turbines, in installations known as wind farms, now generate over 650 gigawatts of power, with 60 GW added each year. ...
s, and are thus often referred to as tidal turbines. They were first conceived in the 1970s during the oil crisis.
[Jones, Anthony T., and Adam Westwood. "Power from the oceans: wind energy industries are growing, and as we look for alternative power sources, the growth potential is through the roof. Two industry watchers take a look at generating energy from wind and wave action and the potential to alter." The Futurist 39.1 (2005): 37(5). GALE Expanded Academic ASAP. Web. 8 October 2009.]
Tidal stream generators are the cheapest and the least ecologically damaging among the
four main forms of
tidal power
Tidal power or tidal energy is harnessed by converting energy from tides into useful forms of power, mainly electricity using various methods.
Although not yet widely used, tidal energy has the potential for future electricity generation. Ti ...
generation.
Similarity to wind turbines
Tidal stream generators draw energy from water currents in much the same way as
wind turbine
A wind turbine is a device that converts the kinetic energy of wind into electrical energy. Hundreds of thousands of large turbines, in installations known as wind farms, now generate over 650 gigawatts of power, with 60 GW added each year. ...
s draw energy from air currents. However, the potential for power generation by an individual tidal turbine can be greater than that of similarly rated wind energy turbine. The higher density of water relative to air (water is about 800 times the density of air) means that a single generator can provide significant power at low tidal flow velocities compared with similar wind speed. Given that power varies with the density of medium and the cube of velocity, water speeds of nearly one-tenth the speed of wind provide the same power for the same size of turbine system; however this limits the application in practice to places where tide speed is at least 2 knots (1 m/s) even close to
neap tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another.
Tide tables c ...
s. Furthermore, at higher speeds in a flow between 2 and 3 meters per second in seawater a tidal turbine can typically access four times as much energy per rotor swept area as a similarly rated power wind turbine.
Types of tidal stream generators
No standard tidal stream generator has emerged as the clear winner, among a large variety of designs. 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 performances and rates of return on investments.
The
European Marine Energy Centre
The European Marine Energy Centre (EMEC) Ltd is a UKAS accredited test and research center focusing on wave and tidal power development based in the Orkney Islands, UK. The centre provides developers with the opportunity to test full-scale grid ...
recognizes six principal types of tidal energy converter. They are horizontal axis turbines, vertical axis turbines, oscillating hydrofoils, venturi devices, Archimedes screws and tidal kites.
Axial turbines
![Cable Tethered Turbine](https://upload.wikimedia.org/wikipedia/commons/e/eb/Cable_Tethered_Turbine.png)
These are close in concept to traditional windmills, but operate under the sea. They have most of the prototypes currently under design, development, testing or operations.
The SR2000, a prototype 2MW floating turbine developed by Orbital Marine Power in Scotland, was operated at the
European Marine Energy Centre
The European Marine Energy Centre (EMEC) Ltd is a UKAS accredited test and research center focusing on wave and tidal power development based in the Orkney Islands, UK. The centre provides developers with the opportunity to test full-scale grid ...
,
Orkney
Orkney (; sco, Orkney; on, Orkneyjar; nrn, Orknøjar), also known as the Orkney Islands, is an archipelago in the Northern Isles of Scotland, situated off the north coast of the island of Great Britain. Orkney is 10 miles (16 km) north ...
, from 2016. It produced 3,200 MWhs of electricity in 12 months of continuous testing. It was removed in September 2018 to make way for the
Orbital O2
The Orbital O2 is a floating 2MW tidal stream generator, tidal turbine that began generating power for the UK grid in July 2021. It was designed and built by Orbital Marine Power Ltd., a privately held company with offices in Orkney and Edinburgh. ...
, the production model, completed in 2021.
Tocardo, a Dutch-based company, has been running tidal turbines since 2008 on the Afsluitdijk, near Den Oever.
Typical production data of tidal generatorshown of the T100 model as applied in Den Oever.
Currently 1 River model (R1) and 2 tidal models (T) are in production with a 3rd T3 coming soon. Power production for the T1 is around 100 kW and around 200 kW for the T2. These are suitable for tidal currents as low 0.4 m/s. Tocardo were declared bankrupt in 2019. QED Naval and HydroWing have joined forces to buy tidal turbine business Tocardo in 2020.
The AR-1000, a 1MW turbine developed by Atlantis Resources Corporation that was successfully deployed at the EMEC facility during the summer of 2011. The AR series are commercial scale, horizontal axis turbines designed for open ocean deployment. AR turbines feature a single rotor set with fixed pitch blades. The AR turbine is rotated as required with each tidal exchange. This is done in the slack period between tides and held in place for the optimal heading for the next tide. AR turbines are rated at 1MW @ 2.65 m/s of water flow velocity.
The
Kvalsund
Kvalsund ( sme, Fálesnuorri and fkv, Valasnuora) is a former municipality in the old Finnmark county in Norway. The municipality is now part of Hammerfest Municipality in Troms og Finnmark county. The municipality existed from 1869 until its ...
installation is south of
Hammerfest
Hammerfest (; sme, Hámmerfeasta ) is a municipality in Troms og Finnmark county, Norway. Hammerfest is the northernmost town in the world with more than 10,000 inhabitants. The administrative centre of the municipality is the town of Hammerfe ...
,
Norway
Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and t ...
at 50m depth of sea. Although still a prototype, the HS300 turbine with a reported capacity of 300 kW was connected to the grid on 13 November 2003. This made it the world's first tidal turbine delivering to the grid. The submerged structure weighed 120 tonnes and had gravity footings of 200 tonnes. Its three-blades were made in glass fibre-reinforced plastic and measured 10 metres from hub to tip. The device rotated at 7 rpm with an installed capacity of 0.3 MW.
Seaflow, a 300 kW Periodflow marine current propeller type turbine was installed by
Marine Current Turbines
Marine Current Turbines Ltd (MCT), is a United Kingdom-based company which is developing tidal stream generators. It is owned by the German automation company, Siemens.
History
MCT was founded in 2000 to develop ideas of tidal power develop ...
off the coast of
Lynmouth
Lynmouth is a village in Devon, England, on the northern edge of Exmoor. The village straddles the confluence of the West Lyn and East Lyn rivers, in a gorge below Lynton, which was the only place to expand to once Lynmouth became as built ...
,
Devon
Devon ( , historically known as Devonshire , ) is a ceremonial and non-metropolitan county in South West England. The most populous settlement in Devon is the city of Plymouth, followed by Devon's county town, the city of Exeter. Devon is ...
, England, in 2003. The 11m diameter turbine generator was fitted to a steel pile which was driven into the seabed. As a prototype, it was connected to a dump load, not to the grid.
In April 2007
Verdant Power
Verdant Power is a maker and installer of tidal power and hydroelectric systems. Their primary device is an underwater turbine, similar to a three-bladed wind turbine, that is designed to capture energy from tidal currents and (precipitation-driv ...
began running a prototype project in the
East River
The East River is a saltwater tidal estuary in New York City. The waterway, which is actually not a river despite its name, connects Upper New York Bay on its south end to Long Island Sound on its north end. It separates the borough of Queens ...
between
Queens
Queens is a borough of New York City, coextensive with Queens County, in the U.S. state of New York. Located on Long Island, it is the largest New York City borough by area. It is bordered by the borough of Brooklyn at the western tip of Long ...
and
Roosevelt Island
Roosevelt Island is an island in New York City's East River, within the borough of Manhattan. It lies between Manhattan Island to the west, and the borough of Queens, on Long Island, to the east. Running from the equivalent of East 46th to 85 ...
in New York City; it was the first major tidal-power project in the United States. 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.
Following the Seaflow trial, a full-size prototype called
SeaGen
SeaGen was the world's first large scale commercial tidal stream generator.
It was four times more powerful than any other tidal stream generator in the world at the time of installation.
It was successfully decommissioned by SIMEC Atlant ...
, 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 and is reported to have fed 150 kW into the grid for the first time on 17 July 2008, and has now contributed more than a gigawatt hour to consumers in Northern Ireland. It is currently the only commercial scale device to have been installed anywhere in the world. SeaGen is made up of two axial flow rotors, each of which drive a generator. The turbines are capable of generating electricity on both the ebb and flood tides because the rotor blades can pitch through 180˚.
![Evopod lighter](https://upload.wikimedia.org/wikipedia/commons/3/3d/Evopod_lighter.jpg)
A prototype semi-submerged floating tethered tidal turbine called
Evopod
Evopod is a unique tidal energy device being developed by a UK-based company Oceanflow Energy Ltd for generating electricity from tidal streams and ocean currents. It can operate in exposed deep water sites where severe wind and waves also make ...
has been tested since June 2008 in Strangford Lough,
Northern Ireland
Northern Ireland ( ga, Tuaisceart Éireann ; sco, label= Ulster-Scots, Norlin Airlann) is a part of the United Kingdom, situated in the north-east of the island of Ireland, that is variously described as a country, province or region. Nort ...
at 1/10 scale. The UK company developing it is called Ocean Flow Energy Ltd. The advanced hull form maintains optimum heading into the tidal stream and is designed to operate in the peak flow of the water column.
In 2010, Tenax Energy of Australia proposed to put 450 turbines off the coast of
Darwin, Australia
Darwin ( ; Larrakia: ) is the capital city of the Northern Territory, Australia. With an estimated population of 147,255 as of 2019, the city contains the majority of the residents of the sparsely populated Northern Territory.
It is the smalle ...
, in the
. The turbines would feature a rotor section approximately 15 metres in diameter with a slightly larger gravity base. The turbines would operate in deep water well below shipping channels. Each turbine is forecast to produce energy for between 300 and 400 homes.
Tidalstream, a UK-based company, commissioned a scaled-down Triton 3 turbine in the Thames in 2003. It can be floated to its site, installed without cranes, jack-ups or divers and then ballasted into operating position. At full scale the Triton 3 in 30-50m deep water has a 3MW capacity, and the Triton 6 in 60-80m water has a capacity of up to 10MW, depending on the flow. Both platforms have man-access capability both in the operating position and in the float-out maintenance position.
European technology and innovation platform for ocean energy (ETIP OCEAN) Powering homes today, Powering nations tomorrow report 2019 makes note of record volumes being supplied through tidal stream technology.
Crossflow turbines
Invented by
Georges Darreius
Georges Jean Marie Darrieus (24 September 1888 – 15 July 1979) was a French aeronautical engineer in the 20th century. He is perhaps most famous for his invention of the Darrieus rotor, a wind turbine
A wind turbine is a device that convert ...
in 1923 and patented in 1929, these turbines can be deployed either vertically or horizontally.
The
Gorlov turbine is a variant of the Darrieus design featuring a helical design that is in a large scale, commercial pilot in South Korea, starting with a 1MW plant that opened in May 2009 and expanding to 90MW by 2013. Neptune Renewable Energy's Proteus project employs a shrouded vertical axis turbine that can be used to form an array in mainly estuarine conditions.
In April 2008, the Ocean Renewable Power Company, LLC (ORPC) successfully completed testing its proprietary turbine-generator unit (TGU) prototype at ORPC's
Cobscook Bay
Cobscook Bay is located in Washington County in the state of Maine. It opens into Passamaquoddy Bay, within the Bay of Fundy. Cobscook Bay is immediately south of the island city of Eastport, the main island of which (Moose Island) straddles the ...
and
Western Passage The Western Passage is an inlet off of the Bay of Fundy just north of Eastport, Maine
Eastport is a city and archipelago in Washington County, Maine, United States. The population was 1,288 at the 2020 census, making Eastport the least-populou ...
tidal sites near
Eastport, Maine
Eastport is a city and archipelago in Washington County, Maine, United States. The population was 1,288 at the 2020 census, making Eastport the least-populous city in Maine. The principal island is Moose Island, which is connected to the mainla ...
. The TGU is the core of the OCGen technology and uses advanced design cross-flow (ADCF) turbines to drive a permanent magnet generator located between the turbines and mounted on the same shaft. ORPC has developed TGU designs that can be used for generating power from river, tidal and deep water ocean currents.
Trials in the
Strait of Messina
The Strait of Messina ( it, Stretto di Messina, Sicilian: Strittu di Missina) is a narrow strait between the eastern tip of Sicily (Punta del Faro) and the western tip of Calabria ( Punta Pezzo) in Southern Italy. It connects the Tyrrhenian Se ...
, Italy, started in 2001 of the
Kobold turbine
A kobold (occasionally cobold) is a mythical sprite. Having spread into Europe with various spellings including "goblin" and "hobgoblin", and later taking root and stemming from Germanic mythology, the concept survived into modern times in Ger ...
concept.
Flow augmented turbines
![Sea Bed Turbine](https://upload.wikimedia.org/wikipedia/commons/4/43/Sea_Bed_Turbine.png)
Using flow augmentation measures, for example a duct or shroud, the incident power available to a turbine can be increased. The most common example uses a
shroud
Shroud usually refers to an item, such as a cloth, that covers or protects some other object. The term is most often used in reference to ''burial sheets'', mound shroud, grave clothes, winding-cloths or winding-sheets, such as the famous Shr ...
to increase the flow rate through the turbine, which can be either axial or crossflow.
The Australian company Tidal Energy Pty Ltd undertook successful commercial trials of efficient
shrouded tidal turbine
The shrouded tidal turbine is an emerging Tidal stream generator, tidal stream technology that has a turbine enclosed in a Venturi effect, venturi shaped shroud or duct (ventuduct), producing a sub atmosphere of low pressure behind the turbine. The ...
s on the
Gold Coast, Queensland
The Gold Coast is a coastal city in the state of Queensland, Australia, approximately south-southeast of the centre of the state capital Brisbane. With a population over 600,000, the Gold Coast is the sixth-largest city in Australia, the nati ...
in 2002. Tidal Energy delivered their shrouded turbine in northern Australia where some of the fastest recorded flows (11 m/s, 21 knots) are found. Two small turbines will provide 3.5 MW. 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.
Oscillating devices
Oscillating devices do not have a rotating component, instead making use of
aerofoil
An airfoil (American English) or aerofoil (British English) is the cross-sectional shape of an object whose motion through a gas is capable of generating significant lift, such as a wing, a sail, or the blades of propeller, rotor, or turbine.
...
sections which are pushed sideways by the flow. Oscillating stream power extraction was proven with the omni- or bi-directional Wing'd Pump windmill. During 2003 a 150 kW oscillating hydroplane device, the
Stingray tidal stream generator
A tidal stream generator, often referred to as a tidal energy converter (TEC), is a machine that extracts energy from moving masses of water, in particular tides, although the term is often used in reference to machines designed to extract energy ...
, was tested off the Scottish coast. The Stingray uses hydrofoils to create oscillation, which allows it to create hydraulic power. This hydraulic power is then used to power a hydraulic motor, which then turns a generator.
Pulse Tidal operate an oscillating hydrofoil device called Pulse generator in the
Humber Estuary
The Humber is a large tidal estuary on the east coast of Northern England. It is formed at Trent Falls, Faxfleet, by the confluence of the tidal rivers Ouse and Trent. From there to the North Sea, it forms part of the boundary between the ...
. Having secured funding from the EU, they are developing a commercial scale device to be commissioned 2012.
The bioSTREAM tidal power conversion system, uses the
biomimicry
Biomimetics or biomimicry is the emulation of the models, systems, and elements of nature for the purpose of solving complex human problems. The terms "biomimetics" and "biomimicry" are derived from grc, βίος (''bios''), life, and μίμησ ...
of swimming species, such as shark, tuna, and mackerel using their highly efficient
Thunniform
Fish locomotion is the various types of animal locomotion used by fish, principally by swimming. This is achieved in different groups of fish by a variety of mechanisms of propulsion, most often by wave-like lateral flexions of the fish's body a ...
mode propulsion. It is produced by Australian company BioPower Systems.
A 2 kW prototype relying on the use of two oscillating hydrofoils in a tandem configuration called
oscillating wing tidal turbine
A tidal stream generator, often referred to as a tidal energy converter (TEC), is a machine that extracts energy from moving masses of water, in particular tides, although the term is often used in reference to machines designed to extract energ ...
has been developed at Laval University and tested successfully near Quebec City, Canada, in 2009. A hydrodynamic efficiency of 40% has been achieved during the field tests.
Venturi effect
Venturi effect devices use a shroud or duct in order to generate a pressure differential which is used to run a secondary hydraulic circuit which is used to generate power. A device, the Hydro Venturi, is to be tested in San Francisco Bay.
Tidal kite turbines
A tidal kite turbine is an underwater kite system or
paravane that converts
tidal energy
Tidal power or tidal energy is harnessed by converting energy from tides into useful forms of power, mainly electricity using various methods.
Although not yet widely used, tidal energy has the potential for future electricity generation. Ti ...
into electricity by moving through the tidal stream. An estimated 1% of 2011's global energy requirements could be provided by such devices at scale.
;History
Ernst Souczek of Vienna, Austria, on August 6, 1947, filed for a paten
US2501696 assignor of one-half to Wolfgang Kmentt, also of Vienna. Their water kite turbine disclosure demonstrated a rich art in water-kite turbines. In similar technology, many others prior to 2006 advanced water-kite and paravane electric generating systems. In 2006, a tidal kite turbine called the
Deep Green Kite was developed by Swedish company Minesto. They conducted its first sea trial in Strangford Lough in Northern Ireland in the summer of 2011. The test used kites with wingspan of 1.4m.
[
In 2013 the Deep Green pilot plant began operation off Northern Ireland. The plant uses ]carbon fiber
Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon compo ...
kites with a wingspan of 8m (or 12m). Each kite has a rated power of 120 kilowatts at a tidal flow of 1.3 meters per second.
;Design
Minesto's kite has a wingspan of . The kite has neutral buoyancy, so doesn't sink as the tide turns from ebb to flow. Each kite is equipped with a gearless turbine
A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating e ...
to generate which is transmitted by the attachment cable to a transformer and then to the electricity grid. The turbine mouth is protected to protect marine life.[
The 14-meter version has a rated power of 850 kilowatts at 1.7 meters per second.][
;Operation
The kite is tethered by a cable to a fixed point. It "flies" through the current carrying a turbine. It moves in a ]figure-eight loop
Figure-eight loop (also figure-eight on a bight, figure-eight follow-through, figure-eight retrace, Flemish loop, or Flemish eight) is a type of knot created by a loop on the bight. It is used in climbing and caving.
The double figure eight is ...
to increase the speed of the water flowing through the turbine tenfold. Force
In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a p ...
increases with the cube of velocity
Velocity is the directional speed of an object in motion as an indication of its rate of change in position as observed from a particular frame of reference and as measured by a particular standard of time (e.g. northbound). Velocity is a ...
, offering the potential to generate 1,000-fold more energy than a stationary generator.[
That maneuver means the kite can operate in tidal streams that move too slowly to drive earlier tidal devices, such as the ]SeaGen
SeaGen was the world's first large scale commercial tidal stream generator.
It was four times more powerful than any other tidal stream generator in the world at the time of installation.
It was successfully decommissioned by SIMEC Atlant ...
turbine.[
The kite was expected to work in flows as low per second, while first-generation devices need over 2.5s. Each kite will have a capacity to generate between 150 and 800 kW. They can be deployed in waters deep.][
]
Tidal stream developers
There are a number of individuals and companies developing tidal energy converters across the world. A database of tidal energy developers is kept up-to-date here
Tidal energy developers
Tidal stream testing
The world's first marine energy test facility was established in 2003 to kick start the development of the wave and tidal energy industry in the UK. Based in Orkney, Scotland, the European Marine Energy Centre
The European Marine Energy Centre (EMEC) Ltd is a UKAS accredited test and research center focusing on wave and tidal power development based in the Orkney Islands, UK. The centre provides developers with the opportunity to test full-scale grid ...
(EMEC) has supported the deployment of more wave and tidal energy devices than at any other single site in the world. EMEC provides a variety of test sites in real sea conditions. Its grid connected tidal test site is located at the Fall of Warness
Muckle Green Holm is an uninhabited island in the North Isles of the Orkney archipelago in Scotland. It is roughly in extent and rises to above sea level, the summit having a triangulation pillar.
Name
'Muckle' is Scots for 'big' or 'larg ...
, off the island of Eday
Eday (, sco, Aidee) is one of the islands of Orkney, which are located to the north of the Scottish mainland. One of the North Isles, Eday is about from the Orkney Mainland. With an area of , it is the ninth-largest island of the archipelago. ...
, in a narrow channel which concentrates the tide as it flows between the Atlantic Ocean and North Sea. This area has a very strong tidal current, which can travel up to 4 m/s (8 knots) in spring tides. Tidal energy developers currently testing at the site include Alstom (formerly Tidal Generation Ltd), ANDRITZ HYDRO Hammerfest, OpenHydro, Scotrenewables Tidal Power, and Voith.
Commercial plans
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 398MW at an offshore site between Scotland's northernmost coast and the island of Stroma. This is the largest planned tidal farm project worldwide right now, and
is also the unique commercial, multi-turbine array to have commenced construction. The first phase of the MeyGen project (Phase 1A) is operational and the subsequent phases are under way.
In 2010, RWE
RWE AG is a German multinational energy company headquartered in Essen. It generates and trades electricity in Asia-Pacific, Europe and the United States. The company is Europe's most climate threatening Company, the world's number two in offsh ...
's npower announced that it is in partnership with Marine Current Turbines to build a tidal farm of SeaGen turbines off the coast of Anglesey
Anglesey (; cy, (Ynys) Môn ) is an island off the north-west coast of Wales. It forms a principal area known as the Isle of Anglesey, that includes Holy Island across the narrow Cymyran Strait and some islets and skerries. Anglesey island ...
in Wales, near the Skerries, with planning permission given in 2013.
"The Skerries project located in Anglesey, Wales, will be one of the first arrays deployed using the Siemens owned Marine Current Turbines SeaGen S tidal turbines. The marine consent for the project was recently awarded, the first tidal array to be consented in Wales. The 10MW array will be fully operational in 2015." - CEO of Siemens Energy Hydro & Ocean Unit Achim Wörner. The project was shelved in 2016 after Marine Current Turbines was acquired by SIMEC Atlantis Energy.
In November 2007, British company Lunar Energy announced that, in conjunction with E.ON, they would be building the world's first deep-sea tidal energy farm off the coast of Pembrokeshire in Wales. It will provide electricity for 5,000 homes.
Eight underwater turbines, each 25 metres long and 15 metres high, are to be installed on the sea bottom off St David's peninsula. Construction is due to start in the summer of 2008 and the proposed tidal energy turbines, described as "a wind farm under the sea", should be operational by 2010. However, it has gone into administration less than a year after developing and testing a 400KW turbine known as DeltaStream in 2015. Lunar Energy dissolved in 2019.
Alderney Renewable Energy Ltd was granted a licence in 2008 and is planning to use tidal turbines to extract power from the notoriously strong tidal race
Tidal race or tidal rapid is a natural occurrence whereby a fast-moving tide passes through a constriction, resulting in the formation of waves, eddies and hazardous currents. The constriction can be a passage where the sides narrow, for example ...
s around Alderney
Alderney (; french: Aurigny ; Auregnais: ) is the northernmost of the inhabited Channel Islands. It is part of the Bailiwick of Guernsey, a British Crown dependency. It is long and wide.
The island's area is , making it the third-largest ...
in the Channel Islands
The Channel Islands ( nrf, Îles d'la Manche; french: îles Anglo-Normandes or ''îles de la Manche'') are an archipelago in the English Channel, off the French coast of Normandy. They include two Crown Dependencies: the Bailiwick of Jersey, ...
. It is estimated that up to 3 GW could be extracted. This would not only supply the island's needs but also leave a considerable surplus for export, using a France-Alderney-Britain cable (FAB Link) which is expected to go online by 2020. This agreement was terminated in 2017.
Nova Scotia Power
Nova Scotia Power Inc. is a vertical integration, vertically integrated electric utility in Nova Scotia, Canada. It is privately owned by Emera and regulated by the provincial government via the Nova Scotia Utility and Review Board (NSUARB). Nov ...
has selected OpenHydro's turbine for a tidal energy demonstration project in the Bay of Fundy, Nova Scotia, Canada and Alderney Renewable Energy Ltd for the supply of tidal turbines in the Channel Islands. OpenHydro was liquidated in 2018.
Pulse Tidal are designing a commercial device in 2007–2009 with seven other companies who are expert in their fields. The consortium was awarded an €8 million EU grant to develop the first device, which will be deployed in 2012 at the Humber estuary and generates enough power for 1,000 homes. Pulse Tidal was liquidated in 2014.
ScottishPower Renewables are planning to deploy ten 1MW HS1000 devices designed by Hammerfest Strom in the Sound of Islay
The Sound of Islay ( gd, Caol Ìle) is a narrow strait between the islands of Islay and Jura off the west coast of Scotland. It is about in extent from north to south and lies between Rubh' a' Mhàil on Islay and Rubh' Aird na Sgitheich on Jura ...
in 2013.
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
Admiralty Inlet is a strait in the U.S. state of Washington connecting the eastern end of the Strait of Juan de Fuca to Puget Sound. It lies between Whidbey Island and the northeastern part of the Olympic Peninsula.
Boundaries
It is generally c ...
, WA. This project is the first grid-connected two-turbine project in the US; installation is planned for the summer of 2015. 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. Each turbine measures 6 meters in diameter, and will generate up to 300 kW of electricity. In September 2014, the project was canceled due to cost concerns.
Energy calculations
Turbine power
Tidal energy converters can have varying modes of operating and therefore varying power output. If the power coefficient of the device "" is known, the equation below can be used to determine the power output of the hydrodynamic subsystem of the machine. This available power cannot exceed that imposed by the Betz limit
Betz's law indicates the maximum power that can be extracted from the wind, independent of the design of a wind turbine in open flow. It was published in 1919 by the German physicist Albert Betz. The law is derived from the principles of conserva ...
on the power coefficient, although this can be circumvented to some degree by placing a turbine in a shroud or duct. This works, in essence, by forcing water which would not have flowed through the turbine through the rotor disk. 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.
The energy available from these kinetic systems can be expressed as:
:
where:
: = the turbine power coefficient
:''P'' = the power generated (in watts)
: = the density of the water (seawater is 1027 kg/m3)
:''A'' = the sweep area of the turbine (in m2)
:''V'' = the velocity of the flow
Relative to an open turbine in free stream, ducted turbines are capable of as much as 3 to 4 times the power of the same turbine rotor in open flow.[ tidal paper on cyberiad.net]
Resource assessment
While initial assessments of the available energy in a channel have focus on calculations using the kinetic energy flux model, the limitations of tidal power generation are significantly more complicated. For example, the maximum physical possible energy extraction from a strait connecting two large basins is given to within 10% by:
:
where
: = the density of the water (seawater is 1027 kg/m3)
:''g'' = gravitational acceleration (9.80665 m/s2)
: = maximum differential water surface elevation across the channel
:= maximum volumetric flow rate though the channel.
Potential sites
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. The following potential sites are under serious consideration:
* Pembrokeshire
Pembrokeshire ( ; cy, Sir Benfro ) is a Local government in Wales#Principal areas, county in the South West Wales, south-west of Wales. It is bordered by Carmarthenshire to the east, Ceredigion to the northeast, and the rest by sea. The count ...
in Wales
* River Severn
, name_etymology =
, image = SevernFromCastleCB.JPG
, image_size = 288
, image_caption = The river seen from Shrewsbury Castle
, map = RiverSevernMap.jpg
, map_size = 288
, map_c ...
between Wales and England
*Cook Strait
Cook Strait ( mi, Te Moana-o-Raukawa) separates the North and South Islands of New Zealand. The strait connects the Tasman Sea on the northwest with the South Pacific Ocean on the southeast. It is wide at its narrowest point,McLintock, A H, ...
in New Zealand
* Kaipara Harbour
Kaipara Harbour is a large enclosed harbour estuary complex on the north western side of the North Island of New Zealand. The northern part of the harbour is administered by the Kaipara District and the southern part is administered by the Auckl ...
in New Zealand
*Bay of Fundy
The Bay of Fundy (french: Baie de Fundy) is a bay between the Canadian provinces of New Brunswick and Nova Scotia, with a small portion touching the U.S. state of Maine. It is an arm of the Gulf of Maine. Its extremely high tidal range is the hi ...
in Canada.
*East River
The East River is a saltwater tidal estuary in New York City. The waterway, which is actually not a river despite its name, connects Upper New York Bay on its south end to Long Island Sound on its north end. It separates the borough of Queens ...
in the United States
*Golden Gate
The Golden Gate is a strait on the west coast of North America that connects San Francisco Bay to the Pacific Ocean. It is defined by the headlands of the San Francisco Peninsula and the Marin Peninsula, and, since 1937, has been spanned by th ...
in the San Francisco Bay
San Francisco Bay is a large tidal estuary in the U.S. state of California, and gives its name to the San Francisco Bay Area. It is dominated by the big cities of San Francisco, San Jose, and Oakland.
San Francisco Bay drains water from a ...
*Piscataqua River
The Piscataqua River (Abenaki: ''Pskehtekwis'') is a tidal river forming the boundary of the U.S. states of New Hampshire and Maine from its origin at the confluence of the Salmon Falls River and Cochecho River. The drainage basin of the river ...
in New Hampshire
New Hampshire is a U.S. state, state in the New England region of the northeastern United States. It is bordered by Massachusetts to the south, Vermont to the west, Maine and the Gulf of Maine to the east, and the Canadian province of Quebec t ...
*The Race of Alderney
Alderney (; french: Aurigny ; Auregnais: ) is the northernmost of the inhabited Channel Islands. It is part of the Bailiwick of Guernsey, a British Crown dependency. It is long and wide.
The island's area is , making it the third-largest ...
and The Swinge
The Swinge is the strait between Alderney and Burhou in the Channel Islands. It often sees a furious tidal race (the Alderney Race), and Braye Harbour which faces it, has a mile-long breakwater to cope with this.
The etymology of the Swinge is ...
in the Channel Islands
The Channel Islands ( nrf, Îles d'la Manche; french: îles Anglo-Normandes or ''îles de la Manche'') are an archipelago in the English Channel, off the French coast of Normandy. They include two Crown Dependencies: the Bailiwick of Jersey, ...
*The Sound of Islay, between Islay
Islay ( ; gd, Ìle, sco, Ila) is the southernmost island of the Inner Hebrides of Scotland. Known as "The Queen of the Hebrides", it lies in Argyll just south west of Jura, Scotland, Jura and around north of the Northern Irish coast. The isl ...
and Jura in Scotland[Islay Energy Trust - Developing Renewables for the community](_blank)
/ref>
*Pentland Firth
The Pentland Firth ( gd, An Caol Arcach, meaning the Orcadian Strait) is a strait which separates the Orkney Islands from Caithness in the north of Scotland. Despite the name, it is not a firth.
Etymology
The name is presumed to be a corruption ...
between Caithness
Caithness ( gd, Gallaibh ; sco, Caitnes; non, Katanes) is a historic county, registration county and lieutenancy area of Scotland.
Caithness has a land boundary with the historic county of Sutherland to the west and is otherwise bounded by ...
and the Orkney
Orkney (; sco, Orkney; on, Orkneyjar; nrn, Orknøjar), also known as the Orkney Islands, is an archipelago in the Northern Isles of Scotland, situated off the north coast of the island of Great Britain. Orkney is 10 miles (16 km) north ...
Islands, Scotland
*Humboldt County, California
Humboldt County () is a county located in the U.S. state of California. As of the 2020 census, the population was 136,463. The county seat is Eureka.
Humboldt County comprises the Eureka–Arcata–Fortuna, California Micropolitan Statistica ...
in the United States
*Columbia River
The Columbia River (Upper Chinook: ' or '; Sahaptin: ''Nch’i-Wàna'' or ''Nchi wana''; Sinixt dialect'' '') is the largest river in the Pacific Northwest region of North America. The river rises in the Rocky Mountains of British Columbia, C ...
, Oregon
Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...
in the United States
*Plaquemines Parish, Louisiana
Plaquemines Parish (; French language, French: ''Paroisse de Plaquemine'', Louisiana French: ''Paroisse des Plaquemines'', es, Parroquia de Caquis) is a Parish (subnational entity), parish located in the U.S. state of Louisiana. With a populat ...
in the Southern United States
* Isle of Wight
The Isle of Wight ( ) is a county in the English Channel, off the coast of Hampshire, from which it is separated by the Solent. It is the largest and second-most populous island of England. Referred to as 'The Island' by residents, the Isle of ...
, England
* Teddington and Ham Hydro
Teddington is a suburb in south-west London in the London Borough of Richmond upon Thames. In 2021, Teddington was named as the best place to live in London by ''The Sunday Times''. Historically in Middlesex, Teddington is situated on a long m ...
at Teddington on the River Thames in the London suburbs, England
Modern advances in turbine
A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating e ...
technology may eventually see large amounts of power generated from the ocean, especially tidal currents using the tidal stream designs but also from the major thermal current systems such as the Gulf Stream
The Gulf Stream, together with its northern extension the North Atlantic Current, North Atlantic Drift, is a warm and swift Atlantic Ocean, Atlantic ocean current that originates in the Gulf of Mexico and flows through the Straits of Florida a ...
, which is covered by the more general term marine current power
Marine currents can carry large amounts of water, largely driven by the tides, which are a consequence of the gravitational effects of the planetary motion of the Earth, the Moon and the Sun. Augmented flow velocities can be found where the underw ...
. Tidal stream turbines may be arrayed in high-velocity areas where natural tidal current flows are concentrated such as the west and east coasts of Canada, the Strait of Gibraltar
The Strait of Gibraltar ( ar, مضيق جبل طارق, Maḍīq Jabal Ṭāriq; es, Estrecho de Gibraltar, Archaic: Pillars of Hercules), also known as the Straits of Gibraltar, is a narrow strait that connects the Atlantic Ocean to the Medi ...
, the Bosporus
The Bosporus Strait (; grc, Βόσπορος ; tr, İstanbul Boğazı 'Istanbul strait', colloquially ''Boğaz'') or Bosphorus Strait is a natural strait and an internationally significant waterway located in Istanbul in northwestern T ...
, and numerous sites in Southeast Asia
Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical United Nations geoscheme for Asia#South-eastern Asia, south-eastern region of Asia, consistin ...
and Australia. Such flows occur almost anywhere where there are entrances to bays and rivers, or between land masses where water currents are concentrated.
Environmental impacts
The main environmental concern with tidal energy
Tidal power or tidal energy is harnessed by converting energy from tides into useful forms of power, mainly electricity using various methods.
Although not yet widely used, tidal energy has the potential for future electricity generation. Ti ...
is associated with blade strike and entanglement of marine organisms as high speed water increases the risk of organisms being pushed near or through these devices. As with all offshore renewable energies, there is also a concern about how the creation of EMF and acoustic outputs may affect marine organisms. Because these devices are in the water, the acoustic output can be greater than those created with offshore wind energy
Offshore wind power or offshore wind energy is the generation of electricity through wind farms in bodies of water, usually at sea. There are higher wind speeds offshore than on land, so offshore farms generate more electricity per amount of c ...
. Depending on the frequency and amplitude of sound generated by the tidal energy devices, this acoustic output can have varying effects on marine mammals (particularly those who echolocate to communicate and navigate in the marine environment such as dolphin
A dolphin is an aquatic mammal within the infraorder Cetacea. Dolphin species belong to the families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontoporiidae (the ...
s and whale
Whales are a widely distributed and diverse group of fully aquatic placental marine mammals. As an informal and colloquial grouping, they correspond to large members of the infraorder Cetacea, i.e. all cetaceans apart from dolphins and ...
s). 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.
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
A scientific echosounder is a device which uses sonar technology for the measurement of underwater physical and biological components—this device is also known as ''scientific sonar''. Applications include bathymetry, seabed, substrate classific ...
) to detect and track the movement of fish both upstream and downstream of each of six turbines. The results suggested (1) very few fish using this portion of the river, (2) those fish which did use this area were not using the portion of the river which would subject them to blade strikes, and (3) no evidence of fish traveling through blade areas.
Work is currently being conducted by the Northwest National Marine Renewable Energy Center ( NNMREC) to explore and establish tools and protocols for assessment of physical and biological conditions and monitor environmental changes associated with tidal energy development.
See also
* Marine energy
Marine energy or marine power (also sometimes referred to as ocean energy, ocean power, or marine and hydrokinetic energy) refers to the energy carried by ocean waves, tides, salinity, and ocean temperature differences. The movement of water in ...
* Renewable energy
Renewable energy is energy that is collected from renewable resources that are naturally replenished on a human timescale. It includes sources such as sunlight, wind, the movement of water, and geothermal heat. Although most renewable energy ...
* Tidal power
Tidal power or tidal energy is harnessed by converting energy from tides into useful forms of power, mainly electricity using various methods.
Although not yet widely used, tidal energy has the potential for future electricity generation. Ti ...
* Wave power
Wave power is the capture of energy of wind waves to do useful work – for example, electricity generation, water desalination, or pumping water. A machine that exploits wave power is a wave energy converter (WEC).
Waves are generated by wind p ...
* Wind turbine
A wind turbine is a device that converts the kinetic energy of wind into electrical energy. Hundreds of thousands of large turbines, in installations known as wind farms, now generate over 650 gigawatts of power, with 60 GW added each year. ...
References
{{DEFAULTSORT:Tidal Stream Generator