Running Head: TIDAL FENCE

Tidal Fence

Fredrico Watson

Holland College

TIDAL FENCE 2

Abstract

Tidal Fence is a hydro turbine that takes advantage of the fast flowing underwater current

for the collection of kinetic energy. The tidal fence is a mix of two already tested systems such as

the tidal barrage and the tidal stream turbine. The turbine has a bit of change like the submerged

tidal stream turbine, meaning that each turbine is needed to be individually placed around the

oceans floor, the tidal fences are either horizontal vertical axis turbines that are mounted together

with a single fence like building blocks. This paper will give you an insight to what a tidal fence

is and where the idea came from. This paper will also tell you the environmental effects,

locations of being placed in The Bahamas and also expectations of the tidal fence.

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Table of ContentsAbstract................................................................................................................................2

Introduction..........................................................................................................................4

Background..........................................................................................................................5

Environmental Impact.........................................................................................................6

Methodology........................................................................................................................7

Generating Power................................................................................................................7

How It Works..................................................................................................................8

Potential...........................................................................................................................8

SETS Requirements.............................................................................................................9

Location...............................................................................................................................9

United Kingdom............................................................................................................10

Scotland.........................................................................................................................10

Canada...........................................................................................................................11

South Korea...................................................................................................................12

France............................................................................................................................12

Conclusion.........................................................................................................................13

Works Cited.......................................................................................................................14

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Introduction                   

Tidal turbine is a manmade machine made to harvest the potential and the kinetic energy

from the sea. Tidal fence is a fence tied together and submerged in the sea. Tidal fences are

effectively a continuous row of tidal stream energy converters (Giles, Godfrey, Bryden,

Myers, O’Nians   Bahaj & Griffiths, 2010).

Many locations such as Anglesey, Portland Bill, Mull of Kintyre, and Dunscansby Head

in the United Kingdom are known as enhanced tidal area. (Draper, Borthwick,

& Houlsby, 2013). Placing a turbine in a lateral limitless flow is hard because getting the power

will cause flow diversion around the collection of the device

(Draper, Borthwick, & Houlsby, 2013). 

There is a higher amount of power that can be generated by turbines in tidal channels as

too many turbines merely block the flow (Garrett & Cummins, 2007). For turbines to reach a

higher power the best option is to line up the turbines equally across the channel flow.

A stand-alone turbine is more effective in a channel than in a limitless flow, but the

current downstream is unbroken between the wake of the turbines and the free stream (Garrett &

Cummins, 2007).  The energy is lost when the streams combine, there are also losses in a long

channel (Garrett & Cummins, 2007). The maximum power that can be acquired is directly

proportional to the piece or size of the turbine that takes up the space of the cross section (Garrett

& Cummins 2007). 

This paper will explain how the tidal fence turbine works and the potential for using tidal

fences to provide clean energy to the Bahamas.

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Background  

After researching current turbine in front of an entrance of a bay, the research showed

that the average power being produce over a tidal cycle is not that much less than a conventional

dam (Garrett & Cummins 2004). The sea level difference from outside to inside the bay, required

to drive the turbines and produce power, can come from a difference in the time of high and low

tides outside and inside the bay, not just from a difference in the tidal range (Garrett & Cummins

2004).The problem with tidal turbines if too many turbines are placed in a single row it will

reduce the flow and the power that can be cultivated from the current. 

There is a maximum average rate at which energy can be cultivated, and it is sometimes

assumed that this is given by the flux of kinetic energy in the undisturbed state through the most

constricted cross-section of a channel where the currents are strongest (Garrett & Cummins

2015). The cost of tidal plants is expensive, and there are very few ideal places to put it. The

frozen sea, low or weak tides, straight shorelines, low tidal rise or fall are some of the

obstructions (Askari, Mirzaei & Abadi 2015). Energy resource is one of the most important and

contentious issues of our time (Pelc & Fujita 2002). The goal was to invest money in becoming

more energy efficient and increased preservation would be the best idea to lower energy use, but

not make as much as an effect for reducing carbon emissions. The thoughts were on the right

track, but it could not be met through demand side management alone (Pelc & Fujita 2002).

As many as two billion people worldwide lack electricity today, and as rapid population

growth in developing countries continues, demand for electricity will almost certainly rise (Pelc

& Fujita 2002). In the 1970s and early 1980 due to improvement in efficiency in the United

States, energy has declined (Pelc & Fujita 2002). Since 2000 there has been a higher demand for

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energy services. Ocean energy was looked into but the ideas such as infrastructure and

knowledge necessary to generate energy from the ocean was already existing.

Some applications of wave, offshore wind, and possibly tidal energy may already be

economically feasible for limited sites, and as research continues, costs of ocean energy are

likely to drop to competitive levels (Pelc & Fujita 2002). Wave energy has long been considered

one of the most promising renewable technologies (Pelc & Fujita 2002). Tidal energy is not only

gigantic but it is more reliable than other renewable such as sun and wind which is available 20

to 30% of the time compared to the 90% of the time tidal is available. The first commercial wave

plant in the world, Limpet 500, was installed on the island of Islay, Scotland, in 2000, and has

been providing power to the grid for the UK since late November 2000.

Environmental Impact

Tidal Plants placed at the mouths of bays made as much of the same environmental

threats as large dams. By altering the flow of saltwater into and out of estuaries, tidal plants

could impact the hydrology and salinity of these sensitive environments (Pelc & Fujita 2002).

Bays are usually used for many marine animals as a nursery and an irreplaceable habitat for the

bay animals. Altering the habitat by the building of a large tidal plant should be avoided.

The building phase for the tidal plant La Rance was intricate. The bay was completely

separated from the ocean for 2-3years and it took a long period of time before the bay reached a

new environmental balance. The construction of the barrage cause problems such as intertidal

area, slower currents, reduce range of the salinities and change bottom water characteristics

which made the change of the marine community. In the future, any new tidal barrages should be

constructed taking care not to close off the bay from the ocean during building, and these plants

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should not be built until detailed environmental assessments demonstrate a minimal impact on

the marine ecosystem (Pelc & Fujita 2002).

Tidal fences are more probable to be environmentally caring. Tidal fences may have

some negative environmental impacts, as they block off channels making it difficult for fish and

wildlife to migrate through those channels (Pelc & Fujita 2002). Blue Energy claims that the

slow-moving turbines allow both fish and water to flow right through the structures, and have no

effect on buildup transport (Pelc & Fujita 2002).

A 20 kW prototype built in 1983 by Nova Energy, Blue Energy’s predecessor, in the St.

Lawrence Seaway found zero recorded fish kill (Pelc & Fujita 2002). In longer-term situations,

some fish kill would be inevitable, but fences could be engineered so that the spaces between the

caisson wall and the rotor foil were large enough for fish to pass through, and the turbines could

be geared down to low velocities (25–50 rpm), keeping fish kill to a minimum (Pelc & Fujita

2002). Marine mammals would be protected by a fence that would keep larger animals away

from the structure and a sonar sensor auto-turbines, making enough electricity for 100,000

households (Pelc & Fujita 2002).

Methodology

I searched using google scholar with keywords such as "Tidal Fence", "Tidal Fence

Location", "Tidal Fence advantages and disadvantages" and "Tidal Fence environment". After I

reviewed the information, I identified the information which was relevant to my paper and would

impact the implementation of tidal turbines in The Bahamas.

Generating Power

Generating power with a tidal turbine is the use of the underwater currents to turn the

shafts underwater. The shafts are connected to a generator and transformer which are above

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water. The tidal fence converts the kinetic energy from the current to electric using the generator

about water.

How It Works

A tidal fence is a series of turbines mounted in a row across passages or canals in coastal

waters. Each turbine is attached to a vertical shaft, and these shafts are mounted in the fence

(Garrett & Cummins 2005). The tidal currents in coastal waters spin the turbines, which turn the

attached generator shaft and produce electricity. The turbine and shaft are the only elements of

the fence under the water; the generator and transformers of these turbines are above water

(Garrett &Cummins 2005).

Potential

It is estimated that the United Kingdom could generate up to 50.2 TW h/yr with tidal

power plants, while Western Europe as a whole could generate up to 105.4 TW h/yr (Pelc &

Fujita 2002). The aim for tidal turbines worldwide is to implement a breaking system that shuts

the system down when marine mammals are detected. The tidal fences would not alter the timing

or amplitude of the tides (Pelc & Fujita 2002). Tidal turbines could be the most environmentally

friendly tidal power option. They do not block channels or estuarine mouths, interrupt fish

migration or alter hydrology (Pelc & Fujita 2002).

Tidal turbines and tidal fences both may offer considerable generating capacity without a

major impact on the ocean, while tidal barrages are probably too damaging to the marine

ecosystem (Pelc & Fujita 2002). Research in tidal energy should focus on turbines, fences and

similar technologies (Pelc & Fujita 2002).These projects should be sited and built so that major

migration channels are left open (Pelc & Fujita 2002). Turbines should turn slowly enough that

fish mortality is minimized and nutrient and sediment transport is largely unaffected (Pelc &

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Fujita 2002). Tidal fences should be built across narrow channels, but not blocking an entire bay

or corridor.

The Bahamas has a lot of untapped potential such as the estuaries located in Freeport,

Nassau, Abaco and the other islands. To harvest current from such areas like the Blue Hole in

Long Island Bahamas would be a great location to place a tidal fence to produce energy even if

it’s only a 10MW turbine. The turbine will greatly help to lower the cost of electricity and a

cleaner way of producing energy.

SETS Requirements

The Severn Embryonic Technologies Scheme goal or aim is to promote the use of

developing tidal technology and solutions for the extraction of energy from the Severn bay.

Develop the new proposal to out the design and placement for the tidal fence turbine. The outline

design, involving the selection for the proper spot to place a fence turbine with the selection of

tidal stream energy converter type that could be feasible for power production. (Giles, Godfrey,

Bryden, Myers, O’Nians, Bahaj & Griffiths 2010). The make of a support building for the tidal

devices and a bridge that could function as a service road for operations and maintenance (Giles

et al., 2010).

The electrical system to convey the power to the most proper grid location. Hire a

number of important technology developers in the development process. Then work on a practice

model of the tidal flows and the withdrawal of energy using of devices to monitor data and

provide the numbers to the developers. Carry out sufficient basic engineering to provide capital

cost estimates of around 15% accuracy (Giles et al., 2010). To grasp a complete understanding of

the importance of operating and maintenance costs including generation lose due to maintenance

cost, breakdowns and system loses. It’s very important to minimize the impact on the

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environment and bay users, by minimizing changes in water levels and giving a navigation gap

for free passage for shipping. (Giles et al., 2010).

Location

Tidal turbines are located in areas such as United Kingdom, Scotland, Canada, South

Korea and France. In each of the location where the turbines were placed, they generated over

10MW. Out of the locations that I found the United Kingdom had the best potential for tidal

power plants.

United Kingdom

It is estimated that the United Kingdom could generate up to 50.2 TW h/yr with tidal

power plants, while Western Europe as a whole could generate up to 105.4 TW h/yr (Bagher et

al., 2015). The total worldwide aptitude is assessed to a breaking system that shuts the system

down when marine mammals are detected (Bagher et al., 2015).

The tidal fences would not have any effect on the currents such as altering the timing or

largeness of the tides (Bagher et al., 2015). Tidal turbines is the most environmentally friendly

tidal power option (Bagher et al., 2015). They do not block channels or bays entrances,

interrupt fish migration or alter currents (Bagher et al., 2015). Tidal turbines and tidal fences

both may offer considerable generating capacity without a major impact on the ocean, while tidal

barrages are probably too damaging to the marine ecosystem (Bagher et al., 2015).

Research in tidal energy should focus on turbines, fences and similar technologies

(Bagher et al., 2015). These projects should be positioned and built so that major migration

channels are left open (Bagher et al., 2015). Turbines should turn slowly enough that fish death

is minimized and nutrient and residue transport is largely unaffected (Bagher et al., 2015). Tidal

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fences should be built across narrow channels, but not blocking an entire bay or corridor (Bagher

et al., 2015).

Scotland

The MeyGen tidal energy project which started 2013 is the largest tidal turbine project

currently developed in Caithness, Scotland. In 2013 the capacity proposed was 86MW and now

the capacity was increased to 298MW (Bagher et al., 2015). The tidal array got their consent

from Askari Mohammad Bagher (Bagher et al., 2015).

The project was a collaboration of tidal companies such as Atlantis Resources and

Morgan Stanley (Bagher et al., 2015). The company that got the full proprietorship of the project

was Atlantis Resources in December 2013 (Bagher et al., 2015).

The start and coming to the end of 2013 the Scottish Government was in control of the

first phase of the 86MW turbine (Bagher et al., 2015). The second phase of the project was to

increase the capacity of the tidal turbine to 398MW by 2020 (Bagher et al., 2015).

The construction is anticipated to start in 2014 and is expected to be working in 2015

(Bagher et al., 2015). They are adding six AR1000 single-rotor turbines to the project. The first

prototype was 22.5m tall with the AR1000 having 18m rotor diameter (Bagher et al., 2015).

They sent the AR1000 to the European Marine Energy Centre in 2011 (Bagher et al., 2015).

Canada

The Annapolis tidal power generating station located in the Annapolis Basin, a sub-bowl

of the Bay of Fundy in Canada, has an installed capacity of 20MW making it the world's third

biggest operating tidal power plant (Bagher et al., 2015).

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It generates 50GWh of electricity annually to power over 4,000 homes (Bagher et al.,

2015). “The plant is operated by Nova Scotia Power, came online in 1984 after four years of

construction. The plant utilizes a path built in the early 1960s, which was originally designed to

serve as a transportation link and also a water control structure to prevent flooding” (Bagher et

al., 2015). The power plant has four single blade turbine and channel gates (Bagher et al.,

2015). The gates are closed when the tides create a head pond in the lower areas of the

Annapolis River upstream of the road (Bagher et al., 2015).” The gates are opened and the water

rushing into the sea drives the turbine to generate power when a head of 1.6m or more is created

between the head pond and sea side with the falling” (Bagher et al., 2015).

South Korea

The Sihwa Lake tidal power station has an output capacity of 254MW (Bagher et al.,

2015). The power station is located on Lake Sihwa which is approximately 4km from the city of

Siheung in Gyeonggi Province of South Korea. It is said to be the world’s biggest tidal power

plants (Bagher et al., 2015). The power plant was opened in August 2011 and owned by Korea

Water Resources Corporation. The power plant uses a 12.5km long seawall for the project. The

wall was constructed in 1994 for flood mitigation and agricultural purposes (Bagher et al., 2015).

“Power is generated on tidal inflows into the 30km2 bowl with the help of ten 25.4MW

submerged bulb turbines. Eight channel type drain gates are used for the water outflow from the

barrage” (Bagher et al., 2015, p.130). The 355.1m tidal power project took 7years to be erected

and operational (Bagher et al., 2015). Daewoo Engineering & Construction was the engineering

company that was used for the construction of the project (Bagher et al., 2015). The annual

generation capacity of the plant is 552.7GWh (Bagher et al., 2015).

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France

The La Rance tidal power plant is located on the bay of the Rance River in Brittany,

France. The tidal power plant has been in use since 1966 making it the world’s oldest and second

biggest tidal power station (Bagher et al., 2015). The power plant is 240MW and is operated by

the Electricity de France (EDF). The power plant has an annual generation capacity of 540GWh

(Bagher et al., 2015). The tidal power plant facility was constructed in the years of 1961 and

1966. The barrage of the tidal plant is 145.1m long with sixed wheel gates and the 163.6m long

dyke (Bagher et al., 2015). The dish area that the tidal plant covers are 22km (Bagher et al.,

2015). The power is produced using 24 reversible bulb turbines with a rated capacity of 10MW

for each one (Bagher et al., 2015). The plant site has an average tidal range from 8.2m, which is

the highest in France (Bagher et al., 2015). The electricity which is produced is sent into a 225kV

national transmission network which power approximately 130,000 households every year in

France (Bagher et al., 2015).

Conclusion

All of my finding showed that implanting a tidal fence can be a substitute for coal in the

future. The amount of energy that can be harness from the tidal fence is very good and there is

almost no repercussions except the construction of the plants. The tidal fence needs a location

with abundant flow and the type of turbine you’re going to put there so that it doesn’t affect the

marine life. In every article or source I found that marine life was always considered and the

turbine would be adjusted so that it doesn’t harm it.

Installing a 50MW tidal fence turbine would be substantial in The Bahamas. The

Bahamas has two small gas fired plants and a steam plant. The switch to tidal to will make a

significant effect on the island. Based on results in other countries such as France being able to

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provide electricity to 130,000 households every year (Bagher et al., 2015). The Bahamas had a

population 301,790 population in 2003 (Zwiernik, 2010).

The 10MW I suggested for the Long Island by Deans Blue Hole will be able to power the

island year round. The island doesn’t consume a lot of energy and the blue hole is about 600ft

depth. It is the largest salt water blue hole and has an entrance below sea level.

.

Works Cited

Bagher, A. M., Vahid, M. M., Reza, B. M., Mohsen, M., & Mahshid, G. (2015). Tidal Energy:

Advantage and disadvantage. Bulletin of Advance Science Research.

Benelghali, S., Benbouzid, M., & Charpentier, J. F. (2007, May 7). Marine Tidal Current

Electric Power Generation Technology: State of the Art and Current Status. Antalya:

HAL archives-ouvertes.

Draper, S., Borthwick, A. G., & Houlsby, G. T. (2013, January 14). Energy Potential of a tidal

fence deployed near a coastal headland. Retrieved from Philosophical Transactions of

the Royal Society of London:

rsta.royalsocietypublishing.org/content/371/1985/20120176

Garrett, C., & Cummins, P. (2005, August 8). The power potential of tidal currents in channels.

Royal Society. Victoria, British Columbia, Canada: The Royal Society.

Garrett, C., & Cummins, P. (2007). The efficiency of a turbine in a tidal channel. Journal of fluid

mechanics. Victoria, British Columbia, Canada: Institute of Ocean Sciences.

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Giles, J., Godfrey, I., Bryden, I., Myers, L., O'Nians, J., Bahaj, A., & Griffiths, J. (2010). An

innovative tidal fence development for the Severn Estuary,. Southampton: School of Civil

Engineering.

Nanayakkara, L., & Nanayakkara, P. (2015). United States of America Patent No. US8987932

B2.

Pelc, R., & Fujita, R. M. (2002). Renewable energy from the ocean. Marine Policy, 26, 471-479.

Zwiernik, A. (2010). Bahamas Minizing and Living with Climate Volatity. Michigan: Laingsburg

High School.