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Institute of Technology of Cambodia

Department of Electric and Energy

(Tidal Energy)

Group: I4 GEE-EE

Assignment Group: 8

Lecturer: ETH OUDAYA

Students:

1. SOT DARO e20120665

2. SRY PHEARATH e20120691

3. SUM CHHENGSE e20120693

4. SUONG CHANPHIREAK e20120700

Year: 2015-2016

i

PREFACE

We are year 4 students from department of electrical and energy engineering at Institute

of Technology of Cambodia. To begin with, we would like to thank to our teacher Mr. ETH

Oudaya who gives us this assignment to research and learn more about the new technologies

that appear in the world of electricity and energy. The goals of this report are to help students

who want to know more information about new evolution of new renewable energy technologies

and also introduce people to the new way to get new energy for living. Additionally, we are

really appreciated to collaborate to do this report in order to improve a part of our knowledge

about this new energy that we didn’t know before. Moreover, the most important of this project

is studying about the renewable energy that we are installed it for producing electricity.

While every attempt has been made to produce a book free of error, the practicality is that

some errors will no doubt appear. I would be most grateful to have these brought to my attention.

I would also be pleased to hear from any users of the book who might have any comments or

suggestions for improvement.

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Table of Contents

Preface…………………………………………………………………………...i

I. Introduction ........................................................................................................... 01

1. Overview ........................................................................................................ 01

2. History of Tidal Power ................................................................................... 02

3. Objective ........................................................................................................ 02

II. Main content .......................................................................................................... 03

i. How Tidal Power works? ..................................................................... 03

A. Tidal Turbines ......................................................................................... 03

A.1 Types of Tidal Turbines .................................................................... 04

Tidal Barrages ......................................................................................... 06 B.

1 Categories of generation ............................................................................ 07

The potential energy contained in a volume of water is given by2 .......... 07

C. Tidal Lagoon ........................................................................................... 08

Geography of Tidal Power ............................................................................. 08 ii.

iii. Economics of Tidal Power ............................................................................. 09

iv. Environment concerns ................................................................................... 12

a. Tidal Barrages .......................................................................................... 12

b. Tidal Turbines .......................................................................................... 13

c. Tidal Lagoons ........................................................................................... 13

v. Pros and Cons of Tidal energy ........................................................................ 13

III. Conclusion ............................................................................................................. 16

IV. Reference ................................................................................................................ 17

1

Tidal energy

I. Introduction

1. Overview [2]

Tidal power exploits energy drawn from the movement of ocean tides to produce

electricity. There are two scenarios in which tides can be tapped for energy. The first is in

changing sea levels. This phenomenon is responsible for the advancing and receding tides on

shorelines. With the help of turbines, incoming tides can be manipulated to generate

electricity. The second way to exploit tidal energy is by sinking turbines to the sea floor where

fast-flowing currents turn generator blades much like wind does with a wind turbine.

Tidal energy is considered renewable because the tides move on a predictable, daily

schedule, depending only on the orbits of the Earth, Moon, and Sun, and are essentially

inexhaustible. Though tidal energy is carbon free, it is not environmentally benign. Concerns

over the health of shoreline and aquatic ecosystems mar this otherwise clean source of energy.

Older tidal barrage technology can devastate fish populations.

In the past, large-scale barrage systems dominated the tidal power scene. But because of

increasingly evident unfavorable environmental and economic drawbacks with this

technology, research into the field of tidal power shifted from barrage systems to tidal current

turbines in the last few decades. This new technology leaves a smaller environmental

footprint than tidal barrages, as turbines are placed in offshore currents avoiding the need to

construct dams to capture the tides along ecologically fragile coastlines. Harnessing tidally-

driven coastal currents cannot yet deliver the sheer amount of power that barrage style

facilities can, like at the 240 MW barrage generating station at La Rance, France.3 However,

and the technology is quickly evolving with numerous test plants popping up around the

globe.

Barred from the mainstream by financial difficulties and environmental concerns, both

tidal barrages and tidal current turbines face challenges in becoming major suppliers of energy

in the 21st century. Recent emphasis on the potential of tidal current turbines, ` and their

reduced effect on shoreline and aquatic ecosystems, suggests that they will replace tidal

barrages as the preferred method of exploiting tidal energy

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2. History of Tidal power

The energy stored in tides been known to people for many centuries. The earliest records

of tidal mills are dated back to the 8th Century CE.7 The tidal mills were mainly used for

grain grinding and were of similar design to the conventional water mills with the exception

of the addition of a dam and reservoir. The industrial revolution increased demand for power

but tidal energy never got off the ground, undercut by cheap fossil fuels and other

developments which offered easier access to power generation. Existing tidal mills became as

obsolescent as pre-industrial water-mills. The first large scale modern tidal electric plant

started to operate in La Rance Estuary, St. Malo, France in the 1960s and has been operating

ever since. In recent years the search for renewable, non-polluting energy sources and the

increase in fossil fuel prices has encouraged renewed interest in tidal power.

Figure 01: The Rance Tidal Power Station

3. Objective

There are 3 types of Tidal energy:

Tidal Barrages

Tidal Stream Generators or Tidal turbine

Tidal Lagoon

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II. Main Content

i. How Tidal Power works?[2]

The energy potential of tidal power depends largely on the rate of flow, which is unique

for each location. Research has shown that little power is generated when only a few turbines

are installed, whereas too many obstructs the flow.

Tidal energy harnesses the natural ebb and flow

of the tides to produce power. Tides are created by

the gravitational pull of the moon and sun,

combined with the rotation of the earth.8 Tidal

energy can be harnessed both in the sea, and in tidal

rivers and estuaries. On some shorelines, water

levels can vary up to 12 metres. It is this drastic

change in water level that makes the first type of

tidal energy — tidal barrages — possible. Tides can

occur once or twice a day depending on location.

Due to the upward gravitational rotation of the

moon, the water level rises gradually until it reaches

its highest point and then gradually falls back to its

lowest point. Also, the tide does not occur at the same time every day, rather it fluctuates over

a period of two weeks or so.

Tidal energy is energy obtained from changing sea levels (the tide moving from

high to low and vice versa.) This renewable energy source has great potential as tides are

much more predictable than wind power and solar energy which are not at all consistent

(seasons, bad weather, etc...).

There are three main ways to harness tidal power, these are:

A. Tidal Turbines

Tidal turbines use similar technology to wind turbines, although their blades are much

shorter and stronger. So a good way to think of them is as underwater windmills. Basically the

water currents turn the turbines, which in turn activate a generator that produces electricity.

These systems work best where there are very strong tidal zones (Norwegian and British

coastlines.) and although it is still in its infancy it does show great promise. The upfront cost

of these tidal stream systems is very high and also installation and maintenance is difficult.

But it’s still cheaper and has less environmental impact than another tidal system which uses

barrages.

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A.1 Types of Tidal stream Generators:

Tidal stream technologies are designed to harness the kinetic energy of the fast flowing

water in tidal areas. Research and development in this emerging field have led to the design of

several types of device to capture this energy:

Horizontal axis turbines :

Horizontal axis turbines work much the same as a conventional wind turbine and

some look very similar in design. A turbine is placed in a tidal stream which causes the

turbine to rotate and produce power. Some turbines may also be housed in

ducting/cowling to create secondary flow effects by concentrating the flow and producing

a pressure difference.

Figure 02: Horizontal axis turbines work

Vertical axis turbines : Vertical axis turbines use the same principle as the horizontal axis turbines only with

a different direction of rotation. A turbine is placed in a tidal stream which causes the

turbine to rotate and produce power.

Figure 03: Vertical axis turbines work

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Reciprocating devices (oscillating hydrofoils) : These have hydrofoils which move back and forth in a plane normal to the tidal

stream, instead of rotating blades. The oscillation motion used to produce power is due to

the lift created by the tidal stream flowing in either side of the wing. One design uses

pistons to feed a hydraulic circuit, which turns a hydraulic motor and generator to produce

power.

Figure 04: Reciprocating devices work

Venturi effect tidal stream devices : The tidal flow is directed through a duct, which concentrates the flow and produces a

pressure difference. This causes a secondary fluid flow through a turbine. The resultant

flow can drive a turbine directly or the induced pressure differential in the system can

drive an air-turbine.

Figure 05: Venturi effect tidal stream devices work

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B. Tidal Barrages

Tidal barrages are very similar to the Dams in hydroelectric plants, except that they are

much larger as they are built across an estuary or bay. The tidal range (difference between

high and low tide) needs to be in excess of five meters for the barrage to be workable. As the

tide comes in, water flows through the dam into the basin. Then when the tide stops the gates

are closed, which traps the water in the basin/estuary.

As the tide goes out gates in the dam which contain turbines are then opened and the flowing

water passes through the turbines, thus generating energy.

Tidal barrages have very high infrastructure costs and are very damaging on the local

environment. Also construction of such dams is a very lengthy project. A good example of

this is the La Rance barrage in France which took over five years to build (it’s the largest tidal

power station in the world.)

A Tidal barrage is a close adaptation of conventional hydroelectric dam technology. This

method blocks off an existing tidal estuary with a dam, or barrage. Movable flood gates,

called sluice gates, on the dam allow incoming tidal waters to fill up in a reservoir. Once the

water reaches its maximum level, the gates close and trap the water. The water in the artificial

estuary is called hydrostatic head.

Figure06: The working of Tidal Barrage

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1 Categories of generation are:

Ebb generation

Flood generation

Pumping

Two basic schemes

Figure 2: Categories of generation

2. The potential energy contained in a volume of water is given by:

E=

where

A is the horizontal area of basin

is the density of water

is the vertical tidal range

is the acceleration due to gravity

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C. Tidal Lagoon

Tidal Lagoons are similar to barrages but have a much lower cost and impact on the

environment. They are self-contained structures cut off from the rest of the sea.

It works in pretty much the same way as a tidal barrage as when the tide raises the lagoon fills

and when it falls the water is then released through the turbines.

Figure 08: Tidal lagoon

ii. Geography of Tidal Power

Tidal power technology is only useful if

it is employed in a prime location. The

success of all types — barrages, turbines,

and lagoons — is contingent upon naturally

occurring geographical elements. Although

all tides produce power, there are only a few

locations where tidal power can be

harnessed. A suitable location must contain

the following:

1. The tide has to rise to unusual height. At

least 7 meter tidal differences are required.

2. Stable conditions for a barrier or turbine to

be built into.

3. Environmental disturbances must be

reduced to a minimum.

Figure09: Bay of Fundy at High Tide, an

ideal location for a tidal barrage.

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The United Kingdom island nation is seeking to take a lead in this field. These locations

include the Pentland Firth, Irish Sea, North Channel, Alderney Race, and Isle of Wight to

Cherbourg, the Orkneys to Shetlands; and the Florida Current.

Major tidal currents also occur in

the Arctic Ocean, Skagerrak-Kattegat,

Hebrides, the Bay of Fundy, the gulfs of

Mexico and St Lawrence, the Amazon

and Rio de la Plata, the Straits of

Magellan, Gibraltar, Messina, Sicily,

and the Bosporus. In the Far East, useful

currents are found near Taiwan and the

Kurile Islands.

Tidal swell — the difference

between the high and low tide marks —

discerns the capabilities of the facility.

High tidal swell locations provide the

greatest potential for tidal development.

Often, good sites are located in areas

where incoming waters must funnel into

narrow channels, including bays, river

mouths, and fjords.

Not all coastlines feature the

minimum 5 meter range needed to make ventures feasible. The world's greatest tidal range is

found in Canada's Bay of Fundy, where tidal swell is over 15 meters.18 Ungava Bay and

numerous estuaries along British Columbia's coast also feature large tidal ranges. The coasts

of Argentina, NW Australia, Brazil, France, India, Korea, the UK, Russia and California,

Maine and Alaska display strong potential for tidal barrages as well.

iii. Economics of Tidal Power

How Much Does it Cost to Construct a Tidal Barrage Power Plant?

Figure 10: Artist's rendition of a tidal fence.

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Large tidal barrages present several unfavorable economic factors: they have large capital

costs and long construction times. This is somewhat balanced out by long plant lives of 100

years for the actual barrage structure, and 40 for the equipment, as well as low operating

costs.

Much depends on the existing geographical and climatic conditions. A main investment

is devoted to the development of the basin. Generally, costs increase for sites that experience

violent winds and waves, as dykes must be built stronger and larger to withstand them.

Tidal energy generation is an emerging technology, yet in its infancy. With only four

main tidal barrage plants operating in the world, clear capital costs are unknown. An estimate

is given by researcher Eleanor Denny. Denny estimates that in order for a facility to be

profitable, its capital cost should be less than €530,000 (~$700,000 USD) per Mega Watt

which with the current technology is not a realistic goal, meaning that so far the industry

produces negative net benefits Tidal plants, however, do benefit from long life spans and a

relatively low cost of operation compared to other types of power plants. For example,

France's La Rance tidal barrage had an initial cost of about $66 million. Despite the high

initial costs, the La Rance power station has been working for almost 45 years to generate

enough electricity for around 300,000 homes and the plant's costs have now been recovered.

As with any tidal barrage, it has seen low operational costs, no fuel costs, and minimal

maintenance. Studies say operation and maintenance costs are typically less than 0.5% of

initial capital costs.

How Much Do Tidal Turbines and Tidal Turbines Cost?

With very few examples of tidal turbine power plant development, it is difficult to

determine a typical cost. To provide a ball-park investment, it is possible to consider two

existing tidal current installations.

Canada's Race Rocks site, where a single turbine generator converts 65 kW of energy,

cost $4,000,000. This figure was met with $3,000,000 investment from project partner

EnCana's Environmental Innovation Fund, and a grant of just under $1 million awarded to

Pearson College and their partners in the project.

On the higher end of the dollar spectrum, we have Ireland's SeaGen, a 1.2 MW generator,

driven by a pair of turbines. This plant produces about 100 times the power generated at Race

Rocks. An investment of around €8.5 million ($11 million USD) made SeaGen a reality.

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What Do Consumers of Tidal Generated Electricity Pay?

SeaGen, the world's first commercial current turbine generator, located in Strangford Lough,

Northern Ireland.

The 240 MW La Rance power plants provide electricity at 3.7 cents/kWh, which is much

more reasonable than the 10.8 cents/kWh charged by thermal plants in the area. The cost is

even lower than that of France's nuclear power, which is 3.8 cents/kWh. Only hydroelectric

plants, at 3.2 cents, are more efficient.

BC Hydro's 2002 Green Energy Study for BC estimated the price of electricity from

potential tidal developments to be in the range of 11-25 cents/kWh. This is a figure based on

past and present technologies, and it is likely that as designs are improved, prices could fall

considerably. The BC Sustainable Energy Association (BCSEA) notes that costs are expected

to decline to around 5-7 cents/kWh.

Economic Effects on Tourism and Fishing

An increase in tourism has been observed at Canada's Annapolis tidal plant, as well as at

France's La Rance plant. More than 40,000 tourists visit the Annapolis facility each year. Sites

have a potential to double as information centers, employing individuals in a range of tourism

positions, in addition to the general operation jobs created by the power plant itself. Temporary

construction jobs are opened up as well during the installation of the facilities.

On the other hand negative environmental effects on marine life can be detrimental to the

fishing industry. Some fishermen have raised concerns over the fact that most identified sites

for tidal power are also key migration routes for fish. Additionally, sedimentation caused by

tidal barrages could kill clams, while also damaging local shellfish fisheries. Studies on

fisheries impacts caused by tidal development are hard to come by, and comparison with the

effects of existing facilities only offers a possible prediction for new power plants. The La

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Rance facility displayed no major effects on the immediate fish community or local fisheries.

The area, however, had a minute fishing industry to begin with and no professional fisherman

After 1960, Impacts are expected to be much more apparent in locations where fish are

abundant and fish passage is repeated by the same populations multiple times over the year,

such as Canada's Bay of Fundy site.

iv. Environment concerns[1]

Tidal power can have effects on marine life. The turbines can accidentally kill swimming

sea life with the rotating blades, although projects such as the one is Strangford feature a

safety mechanism that turns off the turbine when marine animals approach. Some fish may no

longer utilize the area if threatened with a constant rotating or noise-making object. Marine

life is a huge factor when placing tidal power energy generators in the water and precautions

are made to ensure that as many marine animals as possible will not be affected by it.

The Tethys database provides access to scientific literature and general information on the

potential environmental effects of tidal energy.

a. Tidal Barrages

Installing a barrage may change the shoreline within the bay or estuary, affecting a large

ecosystem that depends on tidal flats. Inhibiting the flow of water in and out of the bay, there

may also be less flushing of the bay or estuary, causing additional turbidity (suspended solids)

and less saltwater, which may result in the death of fish that act as a vital food source to birds

and mammals. Migrating fish may also be unable to access breeding streams, and may

attempt to pass through the turbines. The same acoustic concerns apply to tidal barrages.

Decreasing shipping accessibility can become a socio-economic issue, though locks can be

added to allow slow passage. However, the barrage may improve the local economy by

increasing land access as a bridge. Calmer waters may also allow better recreation in the bay

or estuary. Nova Scotia Canada - August 2004, a Humpback whale swam through the

open sluice gate at slack tide, ending up trapped for several days before eventually finding its

way out to the Annapolis Basin

b. Tidal Current Turbines

The main environmental concern with tidal energy 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

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concern about how the creation of EMF and acoustic outputs may affect marine organisms. It

should be noted that because these devices are in the water, the acoustic output can be greater

than those created with offshore wind energy. 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 dolphins and whales. Tidal

energy removal can also cause environmental concerns such as degrading far field 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

near shore ecosystems and processes.

c. Tidal Lagoon

Environmentally, the main concerns are blade strike on fish attempting to enter

the lagoon, acoustic output from turbines, and changes in sedimentation processes. However,

all these effects are localized and do not affect the entire estuary or bay.

v. Pros and Cons of Tidal energy

The worldwide potential for tidal power is estimated to be 700 TWh a year. Currently,

tidal power is early in the development stages and not able to compete with fossil fuels.

However, focus on renewable energy sources and demand for clean energy contributes to a

rapid development of methods to harness this energy source. What are the pros and cons of

tidal energy and what can we expect in the future?

Advantages of Tidal energy

1. Renewable

Tidal Energy is a renewable energy source. This energy source is a result of the

gravitational fields from both the sun and the moon, combined with the earth’s rotation

around its axis, resulting in high and low tides.

It is this difference in potential energy that is the source of power generation from tidal

energy, whether we are talking about stream generators, tidal barrages or more the more

recent technology, dynamic tidal power (DTP).

So, why is tidal energy renewable? Compared to fossil fuels or nuclear reserves, the

gravitational fields from the sun and the moon, as well as the earth’s rotation around its axis

won’t cease to exist any time soon.

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2. Green

Tidal power is an environmentally friendly energy source. In addition to being a

renewable energy, it does not emit any climate gases and does not take up a lot of space.

However, there are currently very few examples from real tidal power plants and their

effects on the environment. An important task is therefore to study and assess these things.

3. Predictable

Tidal currents are highly predictable. High and low tide develop with well-known

cycles, making it easier to construct the system with right dimensions, since we already know

what kind of powers the equipment will be exposed to.

Because of this, even though the turbines that are being used (tidal stream generators

that is) are very similar to wind turbines, both the physical size and the installed capacity has

entirely other limitations.

4. Effective at Low Speeds

Water has 1000 times’ higher density than air, which makes it possible to generate

electricity at low speeds. Calculations show that power can be generated even at 1m/s

(equivalent to a little over 3ft/s).

5. Long Lifespans

We have no reason to believe that tidal power plants are not long lived. This ultimately

reduces the cost these power plants can sell their electricity, making tidal energy more cost-

competitive. The tidal barrage power plant La Rance was opened already in 1966 and still

generates large amounts of electricity.

Disadvantage of Tidal energy

1. Environment Effects

As previously mentioned, the effects tidal power plants have on the environment are not

completely determined yet. We know that these power plants generate green electricity

Tidal barrages rely on manipulation on ocean levels and therefore potentially have the

environmental effects on the environment similar to those of hydroelectric dams.

Technological solutions that will resolve some of these issues are currently being developed.

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2. Close to Land

Tidal power plants needs to be constructed close to land. This is also an area where

technological solutions are being worked on. Hopefully in a few years we can exploit weaker

tidal currents, at locations further out in the sea.

3. Expensive

It is important to realize that the methods for generating electricity from tidal energy is a

relatively are relatively new technologies. It is projected that tidal power will be commercially

profitable within 2020 with better technology and larger scales.

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III. Conclusion

Tides[4]

play a very important role in the formation of global climate as well as the

ecosystems for ocean habitants. At the same time, tides are a substantial potential source of

clean renewable energy for future human generations. Depleting oil reserves, the emission of

greenhouse gases by burning coal, oil and other fossil fuels, as well as the accumulation of

nuclear waste from nuclear reactors will inevitably force people to replace most of our

traditional energy sources with renewable energy in the future. Tidal energy is one of the best

candidates for this approaching revolution. Development of new, efficient, low-cost and

environmentally friendly hydraulic energy converters suited to free-Sow waters, such as triple-

helix turbines, can make tidal energy available worldwide. This type of machine, moreover,

can be used not only for multi-megawatt tidal power farms but also for mini-power stations

with turbines generating a few kilowatts. Such power stations can provide clean energy to

small communities or even individual households located near continental shorelines, straits or

on remote islands with strong tidal currents.

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IV. Reference

1. https://en.wikipedia.org/wiki/Tidal_power

2. http://www.energybc.ca/profiles/tidal.html

3. http://www.slideshare.net/clavinrali/tidal-energy-28557847?related=1

4. http://www.gcktechnology.com/GCK/images/ms0032%20final.pdf