Tidal stream generator
Encyclopedia
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 from run of river or tidal estuarine sites. Certain types of these machines function very much like underwater wind turbine
s, and are thus often referred to as tidal turbines.
Tidal stream generators are the cheapest and the least ecologically damaging among the three main forms of tidal power
generation.
s draw energy from air currents.
As a relatively new technology, though first conceived in the 1970s during the oil crisis, 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, it is simple to see that water speeds of nearly one-tenth of 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 the tide moves at speeds of at least 2 knots (1 m/s) even close to neap tides. Furthermore, at higher speeds in a flow between 2 to 3 metres 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.
The European Marine Energy Centre
categorises them under four heads although a number of other approaches are also being tried.
These are close in concept to traditional windmills operating under the sea and have the most prototypes currently operating. These include:
Kvalsund
, south of Hammerfest
, Norway
. Although still a prototype, a turbine with a reported capacity of 300 kW was connected to the grid on 13 November 2003.
A 300 kW Periodflow marine current propeller type turbine — Seaflow — was installed by Marine Current Turbines
off the coast of Lynmouth
, Devon
, 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.
Since April 2007 Verdant Power
has been running a prototype project in the East River
between Queens
and Roosevelt Island
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 off, and new reinforced turbines were installed in September 2008.
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 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˚.
OpenHydro, an Irish company exploiting the Open-Centre Turbine developed in the U.S., has a prototype being tested at the European Marine Energy Centre
(EMEC), in Orkney, Scotland.
A prototype semi-submerged floating tethered tidal turbine called Evopod
has been tested since June 2008 in Strangford Lough, Northern Ireland
at 1/10 scale. The company developing it is called Ocean Flow Energy Ltd, and they are based in the UK. The advanced hull form maintains optimum heading into the tidal stream and it is designed to operate in the peak flow of the water column.
Tenax Energy of Australia is proposing to put 450 turbines off the coast of the Australian city Darwin, in the Clarence Strait. The turbines feature a rotor section that is approximately 15 metres in diameter with a gravity base which is slighter larger than this to support the structure. The turbines will 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, has commissioned a scaled-down Triton 3 turbine in the Thames, see picture on the right, and photographs maintained on their website. It can be floated out to 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.
Invented by Georges Darreius in 1923 and Patented in 1929, these turbines that can be deployed either vertically or horizontally.
The Gorlov turbine
is a variant of the Darrieus design featuring a helical design which is being commercially piloted on a large scale in S. Korea, starting with a 1MW plant that started in May 2009 and expanding to 90MW by 2013. Neptune Renewable Energy has developed Proteus a shrouded vertical axis turbine which can be used to form an array in mainly estuarine conditions. The Musgrove vertical Axis Wind Turbine with vertical self starting free hinged aerodynamic blades is probably the inspiration for the this turbine.
In late April 2008, Ocean Renewable Power Company, LLC (ORPC) http://www.oceanrenewablepower.com successfully completed the testing of its proprietary turbine-generator unit (TGU) prototype at ORPC's Cobscook Bay
and Western Passage
tidal sites near Eastport, Maine
. The TGU is the core of the OCGen technology and utilizes 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
, Italy, started in 2001 of the Kobold
concept.
to increase the flow rate through the turbine, which can be of either the axial or crossflow type.
The Australian company Tidal Energy Pty Ltd undertook successful commercial trials of efficient shrouded tidal turbine
s on the Gold Coast, Queensland
in 2002. Tidal Energy has commenced a rollout of their shrouded turbine for a remote Australian community in northern Australia where there are some of the fastest flows ever recorded (11 m/s, 21 knots) – two small turbines will provide 3.5 MW. Another larger 5 meter diameter turbine, capable of 800 kW in 4 m/s of flow, is planned for deployment as a tidal powered desalination showcase near Brisbane Australia in October 2008.
Pulse Tidal operate an oscillating hydrofoil device in the Humber estuary. 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
of swimming species, such as shark, tuna, and mackerel using their highly efficient Thunniform 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 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.
'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
in Wales, near the Skerries
.
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 Pembrokshire 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.
British Columbia Tidal Energy Corp. plans to deploy at least three 1.2 MW turbines in the Campbell River
or in the surrounding coastline of British Columbia by 2009.
An organisation named Alderney Renewable Energy Ltd is planning to use tidal turbines to extract power from the notoriously strong tidal race
s around Alderney
in the Channel Islands
. 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.
Nova Scotia Power
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. Open Hydro
Pulse Tidal are designing a commercial device 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 and generate enough power for 1,000 homes. Pulse is in a good position to scale up production because the supply chain is already in place.
ScottishPower Renewables are planning to deploy ten 1MW HS1000 devices designed by Hammerfest Strom in the Sound of Islay.
" 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 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
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. .
where
= the density of the water (seawater is 1027 kg/m³)
Modern advances in turbine
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
, which is covered by the more general term marine current power
. 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 Bosporus
, and numerous sites in Southeast Asia
and Australia. Such flows occur almost anywhere where there are entrances to bays and rivers, or between land masses where water currents are concentrated.
One study of the Roosevelt Island Tidal Energy (RITE, Verdant Power) project in the East River (New York City), utilized 24 split beam hydroacoustic sensors (scientific echosounder
) 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.
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
from moving masses of water, in particular tides, 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
Wind turbine
A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or...
s, and are thus often referred to as tidal turbines.
Tidal stream generators are the cheapest and the least ecologically damaging among the three main forms of tidal power
Tidal power
Tidal power, also called tidal energy, is a form of hydropower that converts the energy of tides into useful forms of power - mainly electricity....
generation.
Similarity to wind turbines
Tidal stream generators draw energy from water currents in much the same way as wind turbineWind turbine
A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or...
s draw energy from air currents.
As a relatively new technology, though first conceived in the 1970s during the oil crisis, 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, it is simple to see that water speeds of nearly one-tenth of 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 the tide moves at speeds of at least 2 knots (1 m/s) even close to neap tides. Furthermore, at higher speeds in a flow between 2 to 3 metres 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
Since tidal stream generators are an immature technology, no standard technology has yet emerged as the clear winner, but a large variety of designs are being experimented with, some very close to large scale deployment. 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
European Marine Energy Centre
The European Marine Energy Centre is a research centre focusing on wave and tidal power development based in the Orkney Islands, UK. It claims to provide developers with the opportunity to test full-scale grid-connected prototype devices in unrivalled wave and tidal conditions...
categorises them under four heads although a number of other approaches are also being tried.
Axial turbines
These are close in concept to traditional windmills operating under the sea and have the most prototypes currently operating. These include:
Kvalsund
Kvalsund
Kvalsund is a municipality in Finnmark county, Norway. The administrative centre of the municipality is the village of Kvalsund. Kvalsund was separated from the municipality of Sørøysund on 1 July 1869....
, south of Hammerfest
Hammerfest
is a city and municipality in Finnmark county, Norway. The municipality encompasses parts of three islands: Kvaløya, Sørøya, and Seiland. Hammerfest was established as a municipality on 1 January 1838...
, Norway
Energy in Norway
Since the discovery of North Sea oil in Norwegian waters during the late 1960s, exports of oil and gas have become very important elements of the economy of Norway...
. Although still a prototype, a turbine with a reported capacity of 300 kW was connected to the grid on 13 November 2003.
A 300 kW Periodflow marine current propeller type turbine — Seaflow — was installed by Marine Current Turbines
Marine Current Turbines
Marine Current Turbines Ltd is a United Kingdom-based company which is developing tidal stream generators.MCT was founded in 2000 to develop ideas of tidal power developed by Peter Fraenkel, who had previously been a founder partner of IT Power, a consultancy established to further the...
off the coast of Lynmouth
Lynmouth
Lynmouth is a village in Devon, England, on the north edge of Exmoor.The village straddles the confluence of the West Lyn and East Lyn rivers, in a gorge below Lynton, to which it is connected by the Lynton and Lynmouth Cliff Railway....
, Devon
Devon
Devon is a large county in southwestern England. The county is sometimes referred to as Devonshire, although the term is rarely used inside the county itself as the county has never been officially "shired", it often indicates a traditional or historical context.The county shares borders with...
, 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.
Since April 2007 Verdant Power
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 river currents...
has been running a prototype project in the East River
East River
The East River is a tidal strait in New York City. It connects Upper New York Bay on its south end to Long Island Sound on its north end. It separates Long Island from the island of Manhattan and the Bronx on the North American mainland...
between Queens
Queens
Queens is the easternmost of the five boroughs of New York City. The largest borough in area and the second-largest in population, it is coextensive with Queens County, an administrative division of New York state, in the United States....
and Roosevelt Island
Roosevelt Island
Roosevelt Island, known as Welfare Island from 1921 to 1973, and before that Blackwell's Island, is a narrow island in the East River of New York City. It lies between the island of Manhattan to its west and the borough of Queens to its east...
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 off, and new reinforced turbines were installed in September 2008.
Following the Seaflow trial, a full-size prototype, called SeaGen
SeaGen
SeaGen is the world's first large scale commercial tidal stream generator. It is four times more powerful than any other tidal stream generator in the world....
, 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˚.
OpenHydro, an Irish company exploiting the Open-Centre Turbine developed in the U.S., has a prototype being tested at the European Marine Energy Centre
European Marine Energy Centre
The European Marine Energy Centre is a research centre focusing on wave and tidal power development based in the Orkney Islands, UK. It claims to provide developers with the opportunity to test full-scale grid-connected prototype devices in unrivalled wave and tidal conditions...
(EMEC), in Orkney, Scotland.
A prototype semi-submerged floating tethered tidal turbine called Evopod
Evopod
Evopod is a unique tidal energy device being developed by a UK-based company Ocean Flow Energy Ltd for generating electricity from tidal streams and ocean currents...
has been tested since June 2008 in Strangford Lough, Northern Ireland
Northern Ireland
Northern Ireland is one of the four countries of the United Kingdom. Situated in the north-east of the island of Ireland, it shares a border with the Republic of Ireland to the south and west...
at 1/10 scale. The company developing it is called Ocean Flow Energy Ltd, and they are based in the UK. The advanced hull form maintains optimum heading into the tidal stream and it is designed to operate in the peak flow of the water column.
Tenax Energy of Australia is proposing to put 450 turbines off the coast of the Australian city Darwin, in the Clarence Strait. The turbines feature a rotor section that is approximately 15 metres in diameter with a gravity base which is slighter larger than this to support the structure. The turbines will 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, has commissioned a scaled-down Triton 3 turbine in the Thames, see picture on the right, and photographs maintained on their website. It can be floated out to 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.
Vertical and horizontal axis crossflow turbines
Invented by Georges Darreius in 1923 and Patented in 1929, these turbines that can be deployed either vertically or horizontally.
The Gorlov turbine
Gorlov helical turbine
The Gorlov helical turbine is a water turbine evolved from the Darrieus turbine design by altering it to have helical blades/foils. It was patented in a series of patents from September 19, 1995 to July 3, 2001 and won 2001 ASME Thomas A. Edison . GHT was invented by Professor Alexander M...
is a variant of the Darrieus design featuring a helical design which is being commercially piloted on a large scale in S. Korea, starting with a 1MW plant that started in May 2009 and expanding to 90MW by 2013. Neptune Renewable Energy has developed Proteus a shrouded vertical axis turbine which can be used to form an array in mainly estuarine conditions. The Musgrove vertical Axis Wind Turbine with vertical self starting free hinged aerodynamic blades is probably the inspiration for the this turbine.
In late April 2008, Ocean Renewable Power Company, LLC (ORPC) http://www.oceanrenewablepower.com successfully completed the testing of its proprietary turbine-generator unit (TGU) prototype at ORPC's Cobscook Bay
Cobscook Bay
Cobscook Bay is located in Washington County in the state of Maine. It opens into the Bay of Fundy immediately south of the city of Eastport and adjacent to Passamaquoddy Bay...
and Western Passage
Western Passage
The Western Passage is an inlet off of the Bay of Fundy just north of Eastport, Maine....
tidal sites near Eastport, Maine
Eastport, Maine
Eastport is a small city in Washington County, Maine, United States. The population was 1,640 at the 2000 census. The principal island is Moose Island, which is connected to the mainland by causeway...
. The TGU is the core of the OCGen technology and utilizes 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
Strait of Messina
The Strait of Messina is the narrow passage between the eastern tip of Sicily and the southern tip of Calabria in the south of Italy. It connects the Tyrrhenian Sea with the Ionian Sea, within the central Mediterranean...
, Italy, started in 2001 of the Kobold
Kobold
The kobold is a sprite stemming from Germanic mythology and surviving into modern times in German folklore. Although usually invisible, a kobold can materialise in the form of an animal, fire, a human being, and a candle. The most common depictions of kobolds show them as humanlike figures the size...
concept.
Flow augmented turbines
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 shroudShrouded tidal turbine
An emerging tidal stream technology is the shrouded tidal turbine enclosed in a Venturi shaped shroud or duct producing a sub atmosphere of low pressure behind the turbine. The shroud allows the turbine to operate at higher output than the turbine alone by increasing the cross-section area used to...
to increase the flow rate through the turbine, which can be of either the axial or crossflow type.
The Australian company Tidal Energy Pty Ltd undertook successful commercial trials of efficient shrouded tidal turbine
Shrouded tidal turbine
An emerging tidal stream technology is the shrouded tidal turbine enclosed in a Venturi shaped shroud or duct producing a sub atmosphere of low pressure behind the turbine. The shroud allows the turbine to operate at higher output than the turbine alone by increasing the cross-section area used to...
s on the Gold Coast, Queensland
Gold Coast, Queensland
Gold Coast is a coastal city of Australia located in South East Queensland, 94km south of the state capital Brisbane. With a population approximately 540,000 in 2010, it is the second most populous city in the state, the sixth most populous city in the country, and also the most populous...
in 2002. Tidal Energy has commenced a rollout of their shrouded turbine for a remote Australian community in northern Australia where there are some of the fastest flows ever recorded (11 m/s, 21 knots) – two small turbines will provide 3.5 MW. Another larger 5 meter diameter turbine, capable of 800 kW in 4 m/s of flow, is planned for deployment as a tidal powered desalination showcase near Brisbane Australia in October 2008.
Oscillating devices
Oscillating devices do not have a rotating component, instead making use of aerofoil 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, 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 in the Humber estuary. 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
Biomimicry
Biomimicry or biomimetics is the examination of nature, its models, systems, processes, and elements to emulate or take inspiration from in order to solve human problems. The term biomimicry and biomimetics come from the Greek words bios, meaning life, and mimesis, meaning to imitate...
of swimming species, such as shark, tuna, and mackerel using their highly efficient Thunniform 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 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.Commercial plans
RWERWE
RWE AG , is a German electric power and natural gas public utility company based in Essen. Through its various subsidiaries, the energy company contributes electricity and gas to more than 20 million electricity customers and 10 million gas customers, principally in Europe...
's npower
Npower (UK)
RWE Npower plc is a UK-based electricity and gas supply generation company, formerly known as Innogy plc. As Innogy plc it was listed on the London Stock Exchange and was a constituent of the FTSE 100 Index...
announced that it is in partnership with Marine Current Turbines to build a tidal farm of SeaGen turbines off the coast of Anglesey
Anglesey
Anglesey , also known by its Welsh name Ynys Môn , is an island and, as Isle of Anglesey, a county off the north west coast of Wales...
in Wales, near the Skerries
The Skerries, Anglesey
The Skerries are a group of sparsely-vegetated rocky islets, with a total area of about , lying 3 km offshore from Carmel Head at the northwest corner of Anglesey, Wales...
.
In November 2007, British company Lunar Energy announced that, in conjunction with E.ON
E.ON
E.ON AG, marketed with an interpunct as E•ON, is the holding company of the world's largest investor-owned energy service provider based in Düsseldorf, Germany. The name comes from the Greek word aeon which means eternity....
, they would be building the world's first deep-sea tidal energy farm off the coast of Pembrokshire 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.
British Columbia Tidal Energy Corp. plans to deploy at least three 1.2 MW turbines in the Campbell River
Campbell River (Vancouver Island)
The Campbell River is a river on Vancouver Island, British Columbia, Canada, draining into Discovery Passage at the northwest end of the Strait of Georgia, at the City of Campbell River, which is named for the river. The Kwak'wala name for the river, or for the village near its mouth The Campbell...
or in the surrounding coastline of British Columbia by 2009.
An organisation named Alderney Renewable Energy Ltd is planning to use tidal turbines to extract power from the notoriously strong tidal race
Tidal race
Tidal race is a natural occurrence whereby a fast moving tide passes through a constriction resulting in the formation of waves, eddies and hazardous currents...
s around Alderney
Alderney
Alderney is the most northerly of the Channel Islands. It is part of the Bailiwick of Guernsey, a British Crown dependency. It is long and wide. The area is , making it the third-largest island of the Channel Islands, and the second largest in the Bailiwick...
in the Channel Islands
Channel Islands
The Channel Islands are an archipelago of British Crown Dependencies in the English Channel, off the French coast of Normandy. They include two separate bailiwicks: the Bailiwick of Guernsey and 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.
Nova Scotia Power
Nova Scotia Power
Nova Scotia Power Inc. is a power generating and delivery company in Nova Scotia. It is privately owned by Emera and regulated by the provincial government via the Nova Scotia Utility and Review Board .-History:...
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. Open Hydro
Pulse Tidal are designing a commercial device 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 and generate enough power for 1,000 homes. Pulse is in a good position to scale up production because the supply chain is already in place.
ScottishPower Renewables are planning to deploy ten 1MW HS1000 devices designed by Hammerfest Strom in the Sound of Islay.
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 on the power coefficient, although this can be circumvented to some degree by placing a turbine in a shroud or ductShrouded tidal turbine
An emerging tidal stream technology is the shrouded tidal turbine enclosed in a Venturi shaped shroud or duct producing a sub atmosphere of low pressure behind the turbine. The shroud allows the turbine to operate at higher output than the turbine alone by increasing the cross-section area used to...
. 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. .
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:- PembrokeshirePembrokeshirePembrokeshire is a county in the south west of Wales. It borders Carmarthenshire to the east and Ceredigion to the north east. The county town is Haverfordwest where Pembrokeshire County Council is headquartered....
in Wales - River SevernRiver SevernThe River Severn is the longest river in Great Britain, at about , but the second longest on the British Isles, behind the River Shannon. It rises at an altitude of on Plynlimon, Ceredigion near Llanidloes, Powys, in the Cambrian Mountains of mid Wales...
between Wales and England - Cook StraitCook StraitCook Strait is the strait between the North and South Islands of New Zealand. It connects the Tasman Sea on the west with the South Pacific Ocean on the east....
in New Zealand - Kaipara HarbourKaipara Tidal Power StationThe Kaipara tidal power station is a proposed tidal power project to be located in the Kaipara Harbour. The project is being developed by Crest Energy, with an ultimate size of 200MW at a cost of $700 million....
in New Zealand - Bay of FundyBay of FundyThe Bay of Fundy is a bay on the Atlantic coast of North America, on the northeast end of the Gulf of Maine between the Canadian provinces of New Brunswick and Nova Scotia, with a small portion touching the U.S. state of Maine...
in Canada. - East RiverEast RiverThe East River is a tidal strait in New York City. It connects Upper New York Bay on its south end to Long Island Sound on its north end. It separates Long Island from the island of Manhattan and the Bronx on the North American mainland...
in the USA - Golden GateGolden GateThe Golden Gate is the North American strait connecting San Francisco Bay to the Pacific Ocean. Since 1937 it has been spanned by the Golden Gate Bridge...
in the San Francisco BaySan Francisco BaySan Francisco Bay is a shallow, productive estuary through which water draining from approximately forty percent of California, flowing in the Sacramento and San Joaquin rivers from the Sierra Nevada mountains, enters the Pacific Ocean... - Piscataqua RiverPiscataqua RiverThe Piscataqua River, in the northeastern United States, is a long tidal estuary formed by the confluence of the Salmon Falls and Cocheco rivers...
in New HampshireNew HampshireNew Hampshire is a state in the New England region of the northeastern United States of America. The state was named after the southern English county of Hampshire. It is bordered by Massachusetts to the south, Vermont to the west, Maine and the Atlantic Ocean to the east, and the Canadian... - The Race of AlderneyAlderneyAlderney is the most northerly of the Channel Islands. It is part of the Bailiwick of Guernsey, a British Crown dependency. It is long and wide. The area is , making it the third-largest island of the Channel Islands, and the second largest in the Bailiwick...
and The SwingeThe SwingeThe Swinge is the strait between Alderney and Burhou in the Channel Islands. It often sees a furious tidal race, and Braye Harbour which faces it, has a mile long breakwater to cope with this....
in the Channel IslandsChannel IslandsThe Channel Islands are an archipelago of British Crown Dependencies in the English Channel, off the French coast of Normandy. They include two separate bailiwicks: the Bailiwick of Guernsey and the Bailiwick of Jersey... - The Sound of Islay, between IslayIslay-Prehistory:The earliest settlers on Islay were nomadic hunter-gatherers who arrived during the Mesolithic period after the retreat of the Pleistocene ice caps. In 1993 a flint arrowhead was found in a field near Bridgend dating from 10,800 BC, the earliest evidence of a human presence found so far...
and JuraJura, ScotlandJura is an island in the Inner Hebrides of Scotland, situated adjacent and to the north-east of Islay. Part of the island is designated as a National Scenic Area. Until the twentieth century Jura was dominated - and most of it was eventually owned - by the Campbell clan of Inveraray Castle on Loch...
in Scotland - Pentland FirthPentland FirthThe Pentland Firth , which is actually more of a strait than a firth, separates the Orkney Islands from Caithness in the north of Scotland.-Etymology:...
between CaithnessCaithnessCaithness is a registration county, lieutenancy area and historic local government area of Scotland. The name was used also for the earldom of Caithness and the Caithness constituency of the Parliament of the United Kingdom . Boundaries are not identical in all contexts, but the Caithness area is...
and the Orkney Islands, ScotlandScotlandScotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the... - Humboldt County, CaliforniaHumboldt County, CaliforniaHumboldt County is a county in the U.S. state of California, located on the far North Coast 200 miles north of San Francisco. According to 2010 Census Data, the county’s population was 134,623...
in the United StatesUnited StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district... - Columbia River, Oregon in the United StatesUnited StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
Modern advances in turbine
Turbine
A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...
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
Gulf Stream
The Gulf Stream, together with its northern extension towards Europe, the North Atlantic Drift, is a powerful, warm, and swift Atlantic ocean current that originates at the tip of Florida, and follows the eastern coastlines of the United States and Newfoundland before crossing the Atlantic Ocean...
, which is covered by the more general term marine current power
Marine current power
Marine current power is a form of marine energy obtained from harnessing of the kinetic energy of marine currents, such as the Gulf stream. Although not widely used at present, marine current power has an important potential for future electricity generation...
. 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
Strait of Gibraltar
The Strait of Gibraltar is a narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates Spain in Europe from Morocco in Africa. The name comes from Gibraltar, which in turn originates from the Arabic Jebel Tariq , albeit the Arab name for the Strait is Bab el-Zakat or...
, the Bosporus
Bosporus
The Bosphorus or Bosporus , also known as the Istanbul Strait , is a strait that forms part of the boundary between Europe and Asia. It is one of the Turkish Straits, along with the Dardanelles...
, and numerous sites in Southeast Asia
Southeast Asia
Southeast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...
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
Very little direct research or observation of tidal stream systems exists. Most direct observations consist of releasing tagged fish upstream of the device(s) and direct observation of mortality or impact on the fish.One study of the Roosevelt Island Tidal Energy (RITE, Verdant Power) project in the East River (New York City), utilized 24 split beam hydroacoustic sensors (scientific echosounder
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...
) 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.