Hydropower

2012

University of Oulu

Odediran Dare Peter

(2302955)

Table of Contents

1.0 Introduction ........................................................................................................................................... 3

1.1 History of hydropower .......................................................................................................................... 3

1.2 Hydropower as a Source of Renewable Energy .................................................................................... 3

1.3 How Hydropower Works ....................................................................................................................... 4

2.0 Impact of Climate Change on Hydropower Project ............................................................................... 4

2.1 Changes in River Flow (Runoff).............................................................................................................. 4

2.2 Climate Variability ................................................................................................................................. 5

2.3 Changes in Sediment Loads ................................................................................................................... 5

3.0 Hydropower and the Environment ........................................................................................................ 6

3.1 Social Impacts ........................................................................................................................................ 6

3.2 Environmental Impacts .......................................................................................................................... 6

4.0 Conclusion ............................................................................................................................................. 7

5.0 References ............................................................................................................................................. 7

1.0 Introduction

Hydropower (from hydro, meaning water) is energy that comes from the force of moving water. The fall

and movement of water is part of a continuous natural cycle called the water cycle. Energy from the sun

evaporates water in the Earth’s oceans and rivers and draws it upward as water vapor. When the water

vapor reaches the cooler air in the atmosphere, it condenses and forms clouds. The moisture eventually

falls to the Earth as rain or snow, replenishing the water in the oceans and rivers. Gravity drives the water,

moving it from high ground to low ground. The force of moving water can be extremely powerful.

1.1 History of hydropower

Hydropower has been used for centuries. The Greeks used water wheels to grind wheat into flour more

than 2,000 years ago. In the early 1800s, American and European factories used the water wheel to power

machines. The water wheel is a simple machine. The water wheel is located below a source of flowing

water. It captures the water in buckets attached to the wheel and the weight of the water causes the wheel

to turn. Waterwheels convert the potential energy (gravitational energy) of the water into motion. That

energy can then be used to grind grain; drive sawmills, or pumps water. The first hydroelectric power plant

was installed in Cragside, Rothbury, England in 1870. Industrial use of hydropower started in 188 in Grand

Rapids, Michigan, when a dynamo driven by a water turbine was used to provide theatre and storefront

lighting. In 1881, a brush dynamo connected to a turbine in a fl our mill provided street lighting at Niagara

Falls, New York. The breakthrough came when the electric generator was coupled to the turbine and thus

the world’s first hydroelectric station (of 12.5 kW capacity) was commissioned on 30 September 1882 on

Fox River at the Vulcan Street Plant, Appleton, Wisconsin, USA, lighting two paper mills and a residence.

Hydropower plants (HPP) today span a very large range of scales, from a few watts to several GW. The

largest projects, Itaipu in Brazil with 14,000 MW 2 and Three Gorges in China with 22,400 MW,3 both

produce between 80 to 100 TWh /yr (288 to 360 PJ/yr). Hydropower projects are always site-specifi c and

thus designed according to the river system they inhabit.

Shows: Historical regional hydropower generation from 1965 to 2009

1.2 Hydropower as a Source of Renewable Energy

Hydropower is called a renewable energy source because the water on Earth is continuously replenished by

precipitation. As long as the water cycle continues, we won’t run out of this energy source. The plants do

not consume the water that drives the turbines and after power generation, the water is still available for

other essential uses. The use of hydropower prevents the burning of 22 billion gallons of oil or 120 million

tons of coal each year and the carbon emission avoided by the nation’s hydroelectric industry are the

equivalent of an additional 67 million passenger cars on the road.

Source: www.need.org

1.3 How Hydropower Works

A typical hydropower plant is a system with three parts:

� i) A power plant where the electricity is produced;

�ii) A dam that can be opened or closed to control water flow; and

�iii) A reservoir (artificial lake) where water can be stored.

To generate electricity, a dam opens its gates to allow water from the reservoir above to flow down

through large tubes called penstocks. At the bottom of the penstocks, the fast-moving water spins the

blades of turbines. The turbines are connected to generators to produce electricity. The electricity is then

transported via huge transmission lines to a local utility company.

Source: http://www.need.org/needpdf/infobook_activities/SecInfo/

2.0 Impact of Climate Change on Hydropower Project

The future global climate is uncertain and thus poses some risk for the sector. The crucial question and

challenge then is what will be the impact of climate change on global hydropower generation and what are

the resulting regional variations in hydropower generation potential? There are three main impacts of

climate changes on hydropower projects.

2.1 Changes in River Flow (Runoff)

The available discharge of a river may change, since hydrology is usually related to local weather

conditions, such as temperature and precipitation in the catchment area. This will have a direct influence

on economic and financial viability of a hydropower project. Moreover, hydropower operations may have

to be reconsidered to the extent that hydrological periodicities or seasonality change. The reason is that, if

the flow of water changes, different power generating operations, e.g., peak versus base load, would be

possible using other designs for water use, such as reservoirs and this directly affecting the resource

potential for hydropower generation.

Shows: Future potential change in runoff (IPCC, 2007)

2.2 Climate Variability

An expected increase in climate variability may trigger extreme climate events, i.e. floods and droughts. For

instance, a hydrological model indicates a great risk of Bangladeshi suffering from extreme floods, which

are led by substantial increases in (mean) peak discharges in the regional three major rivers, Ganges,

(Brahmaputra and Meghna Mirza, 2002). One of his scenarios predicts that the volume of water in the

Ganges would increase by 5 to 15 percent, depending on changes in temperature.

Source: Ipcc report

Large-scale changes in annual runoff (water availability, in percent) for the period 2090 to 2099, relative to

1980 to 1999. Values represent the median of 12 climate model projections using the SRES A1B scenario.

White areas are where less than 66% of the 12 models agree on the sign of change and hatched areas are

where more than 90% of models agree on the sign of change. Source: IPCC (2007a).

2.3 Changes in Sediment Loads

Closely related to the previous impacts, changing hydrology and possible extreme events must of necessity

impact sediment risks and measures. More sediment, along with other factors such as changed

composition of water, could raise the probability that a hydropower project suffers greater exposure to

turbine erosion. When a major destruction actually occurs, the cost of recovery would be enormous. An

unexpected amount of sediment will also lower turbine and generator efficiency, resulting in a decline in

energy generated.

3.0 Hydropower and the Environment

Hydropower dams can cause several environmental problems, even though they burn no fuel. Damming

rivers may permanently alter river systems and wildlife habitats. Fish, for one, may no longer be able to

swim upstream and hydro plant operations may also affect water quality by churning up dissolved metals

that may have been deposited by industry long ago. Hydropower operations may increase silting, change

water temperatures, and lower the levels of dissolved oxygen.

3.1 Social Impacts

Social aspects associated with development of hydro projects are mainly associated with transformation of

land use in the project area, and displacement of people living in the reservoir area. Relocating people from

the reservoir area is the most challenging social aspect of hydropower, leading to significant concerns

regarding local culture, religious beliefs, and effects associated with inundating burial sites. While there can

never be a 100 percent satisfactory solution to involuntary resettlement, enormous progress has been

made in the way the problem is handled. The countries in Asia and Latin America where resettlement is a

major issue has developed comprehensive strategies for compensation and support for people who are

impacted. The keys to success are clearly: timely and continuous communications between developers and

those affected; adequate compensation, support and long term contact; and efforts to ensure that the

disruption of relocation is balanced by some direct benefits from the project.

3.2 Environmental Impacts

The construction of dams for hydropower could lead to following in the water body:

Sedimentation

Sedimentation occurs when weathered rock, organic and chemical materials transported in a river system

are trapped in a reservoir. Over time these sediments build up and begin to occupy a significant volume of

the original storage capacity. While large dams and reservoirs are often designed for an operating life of

100 years, there are cases where reservoirs have faced sedimentation problems within a much shorter

time.

Water Quality

Changes in water quality are potential outcomes from locating a dam in a river. Effects are often

experienced both upstream and downstream of a dam. Some of the effects can be increased or decreased

dissolved oxygen, increases in total dissolved gases, modified nutrient levels, thermal modification and

heavy metal levels which could lead to the following ecological changes:

· permanent loss of habitat and species biotopes through inundation

· loss of flooding

· fluctuating water level and habitat change

· introduction and dispersal of exotic species

· obstacles to fish migration

4.0 Conclusion

Hydropower has advantages, if proper mitigation is carried out during the construction because its fuel

supply (flowing Water) is clean and is renewed yearly by snow and rainfall. Furthermore, hydro plants do

not emit pollutants into the air because they burn no fuel. With growing concern over greenhouse gas

emissions and increased demand for electricity, hydropower may become more important in the future.

Hydropower facilities offer a range of additional benefits. Many dams are used to control flooding and

regulate water supply, and reservoirs provide lakes for recreational purposes, such as boating and fishing.

5.0 References

Byman Hamududu and Aanund Killingtveit. (2012). Assessing Climate Change Impacts on Global

Hydropower. energies. 5 (2), 305-322;

John p.. (1998). Hydroelectricity. Available: en.wikipedia.org/wiki/Hydroelectricity. Last accessed 30th oct

2012.

http://www.renewableenergyworld.com/rea/tech/hydropower

http://www.need.org/needpdf/infobook_activities/SecInfo/

WIND POWER

Project Report

Rajib Maharjan ; Student no:-2304445

Contents

· Back ground

· Wind in world

· Wind Power system

· Features of system design

· Maximum Power Operation

· System Control

· Environmental Aspects

· Conclusion

· Reference

Background

· Initial 5000 years ago the use of wind power was to sail ships in the Nile which later on

used by Europeans for grind grains and pump water in 1700s and 1800s. The first use of

windmill for the generation of electricity was carried out in U.S.A in 1890.Nowadays,

large wind-power plants are used all over the world with electric utilities for the supply of

economical clean power. In recent past the largest size of turbine has been 300kw which

on present developed to the capacity of 500 to 1000kw and some of prototypes of modern

multi-megawatt wind turbines are under test in several countries. The improvement of

turbine design and plant utilization had made wind energy as the least-cost powers source

which used to be 35cent per kWh in 1980 to less than 5cent per kWh in the present

situation. The major factors which accelerated the development of wind-power

technology are as follows:

· The availability of the high-strength composites for the constructing large low-cost

blades.

· The lowering of prices of the power electronics.

· Up to 95% operation plant’s improvement.

· The economic scale as the size enlargement of turbines and plants.

· The improvement in capacity factor by the field experience.

Wind in world

Wind energy is a converted form of solar energy which is produced by the nuclear fusion of

hydrogen (H) into helium (He) in its core. The H → He fusion process creates heat and

electromagnetic radiation streams out from the sun into space in all directions. Though only a

small portion of solar radiation is intercepted by the earth, it provides almost all of earth’s energy

needs. Wind results from the movement of air due to atmospheric pressure gradients. Wind flows

from regions of higher pressure to regions of lower pressure. The larger the atmospheric pressure

gradient, the higher the wind speed and thus, the greater the wind power that can be captured

from the wind by means of wind energy-converting machinery. The generation and movement of

wind are complicated due to a number of factors. Among them, the most important factors are

uneven solar heating, the Coriolis Effect due to the earth’s self-rotation, and local geographical

conditions.

The wind energy is the most promising new sources of electric power which is promoted by

many countries by national programs and market incentives. The International Energy Agency

(IEA), with funding from 14 countries, supports joint research projects and information exchange

on wind-power development. These countries are Austria, Canada, Denmark, Finland, Germany,

Italy, Japan, the Netherlands, New Zealand, Norway, Spain, Sweden, the United Kingdom, and

the United States of America.

The installed wind power in various counties in 1994, 1995 and 19997 can be show in tabular

form as follows:

Country 1994

MW

1995

MW

1997

MW

Growth

1994-1995

Percent

Annual

Growth Rate

1995-97

Percent

Germany 643 1136 2079 76.7 35.2

United States 1785 1828 2000 2.4 4.7

Denmark 540 614 1141 13.7 36.3

India 182 565 1000 210 33.0

Netherlands 153 259 325 69 12.0

United

Kingdom

147 193 308 31 26.3

Spain 72 145 455 100 77.1

China 30 36 — 20 —

TOTAL 3552 4776 7308 35.4 23.7

(Source: United States data from Energy Information Administration, Annual Energy Outlook

1997, DOE/EIA Report No. 0383-97, Table A17, Washington, D.C., December1996. Other

countries data from the American Wind Energy Association, Status Report of International Wind

Projects, Washington, D.C., March 1996.)

Projected Wind Capacity Addition in

Megawatts between 1994 and 2000

Country Addition planned

Megawatts United Kingdom

Spain

Germany

India

China

Mexico

Argentina

Chile

Australia

New Zealand

100–300

150–250

200–350

700–1200

350–600

150–300

100–150

100–200

50–75

50–100

Total 1950–3525

(Source: American Wind Energy Association/Arthur D. Little, Inc.)

Wind Power System

The wind power system consists of one or more units which operates electrically in parallel and

have following components:-

· The tower

· The wind turbine with two or three blades.

· The yaw mechanism such as the tail vane.

· The mechanical gear.

· The electrical generator.

· The speed sensors and control.

The modern system of the power plant has some additional components which are as follows:-

· The power electronics.

· The control electronics, usually incorporating a computer.

· The battery for improving the load availability in stand-alone mode.

· The transmission link connecting to the area grid.

Since there is large moment of inertia of rotor, there must be some design units which controls

speed during power production and stopping turbine when required for which eddy current or

other breaks are used to stop turbine in case of emergency or routine maintenance. In case of

multiple winds tower farm there must be a single control system for each one of the tower which

must be operated from remote location for operation and safety.

Fig:- Components of Wind power system

Tower

The wind tower supports turbine and consists of the nacelle which is comprise of mechanical

gear, electric generator, yaw mechanism, and the stall control. The height of tower depends on

the diameter of the rotor generally are made slightly taller than the rotor diameter. Steel and

concrete are two material used for construction in which structural dynamics which causes in

vibration of tower and results in fatigue cycle due to fluctuation in wind speed for which

resonance frequency is avoided from the tower, the rotor and the nacelle with the comparison to

the wind fluctuation frequencies.

Turbine Blades

The blades of turbine are made up of high density wood or glass fiber consisting epoxy

composite which are two or three in numbers. The fatigue failure must be avoided which is done

by controlling rotor speed and maintain it below the allowable limit also electric generator must

be protected from overloading and overheating. While designing the maximum load point which

is at blade root must be considered and the total cost of the blades is kept below 10% of the total

installation cost.

Fig:- Wind turbine with 3 blades

Yaw Control

It is to maintain the orientation of rotor in direction of the wind which is as tail vane or complex

which controls large moment of inertia during rotation of blades which produce large sound. So,

controlled jaw is required for the control of sound to the local ordinance level during blade

rotation.

Speed Control

The speed control device depends on the size to wind turbines in which consist of pitch control

and the power electronic. For the small machines simple, low cost power and speed control is

sufficient. The speed control method can be described as follows:-

· When the system the turbine, the electrical generator is designed to withstand speed

under high wind there is no speed control.

· For the conditions when speed exceeds design speed in which rotor axis is shifted out of

wind direction yaw and tilt control is used.

· The pitch control also can be used which changes the pitch of blade is change accordance

to the change in wind speed regulating the rotor speed.

· Another method is stall control in which the blades are shifted to the position in which

they are stalled as the wind speed excides its limit. After gust has gone turbine must be

restarted.

Turbine Rating

The turbine rating is important factor which defines the size of the induction generator, the plant

transformer, cable connection to the substation, and interfacing of transmission link in the grid.

The turbine power depends on the wind speed so for the better performance turbine and

generator performance must be stimulated.

For the design of wind turbines the Specific rated capacity is compared, which is defined as:

SRC = Generator electrical capacity/ Rotor swept area

For the 300/30 wind turbine, the specific rated capacity is 300/3.14*152=0.42 kW/m2. The

specific rated capacity increases with the diameter, giving a favorable economy of scale to large

machine.

The Features of System Design

Number of blades

There are numerous wind power have been built which consist of 2 to 40 or more blades. The

high numbers of blades are used in water pumping application which requires high starting

torque but the modern wind power consists of tip-speed ratio rotors which have 2 or 3 blades and

are used for generation electric power. The number of blades is decided on the basis of various

factors which are as follows:-

· Effect on power coefficient

· Deign tip-speed ratio

· Overall cost

· Weight of nacelle

· Structural dynamics

· Available means for limiting yaw rate and gyroscopic fatigue.

Rotor Upwind or Downwind

Both types of rotor are used at present. The operation with rotor upwind gives high power which

eliminates shadow on blades resulting low noise, low blade fatigue and smoother power output

whereas downwind rotor allow to use free yaw system also allows blades to deflect anywhere

from tower when loaded.

Horizontal Axis versus Vertical Axis

In present most of the turbines are built have horizontal axis even though turbines with vertical

axis many advantages such as it doesn’t requires yaw mechanism for continuous orientation in

the direction of wind also with vertical drive shaft installation of gearbox and electrical generator

on ground which makes structures simpler. The main reason by which the use is discarded is that

its output cannot be easily controlled in high simply by changing the blade pitch.

Spacing of the Towers

Fig:- Orientation and spacing of wind turbine in farm

While install wind towers in a wind farm certain spacing between the wind towers must be

maintained which minimize power cropping. The spacing is dependent on terrain, wind

direction, the speed and the turbine size and the minimum speed which must be maintained while

installing in row is 8 to 12-rotor diameters apart in the wind direction and 1.5 to 3- rotor

diameters in crosswind direction. For the optimum use of land following studies are applied

while installing wind turbines:-

· The installation of large turbines cost less per MW capacity which also less land area.

· By using few large machines reduces the MWh energy crop per year since downtime of

single machine has large impact on energy output.

· In few large few machines the fluctuations and electrical transients cost more for the

filtering of power and voltage fluctuation or degrade power quality from the grid.

Maximum Power Operation

For the maximum power operation which generates electricity 20to 30 percent more per year is

by operating wind turbine at a constant tip-speed ratio which requires a control scheme for

operating in variable speed. There are two possible schemes for variable speed operation which

are as follows:-

Constant Tip-Speed Ratio Scheme

It is based on the fact that when optimum tip-speed ratio is maintained at all wind speed

maximum energy can be obtained. The optimum value is stored as reference TSR in control

computer with this constant reference the turbine speed maintained. The continuous wind speed

is measured which compared with blade tip-speed and the error signal is fed to control system

according to the error in control system the speed of turbine is maintained.

Fig:-Diagrammatic representation of constant tip-speed ratio

Peak Power Tracking Scheme

It is based on the power versus speed curve which shows a single well-defined peak. If turbine is

operated in peak-point, a small increase or decrease in turbine speed doesn’t effect on the power

output as the peak point locally lies in a flat neighborhood. The necessary condition for the speed

to be at the maximum power point is as follows:-

dp/dw=0

The speed is continuously increased or decreased in small quantity, the power measured

continuously and continuous evaluation off

is increased to generate more power, if ratio is –ve power generation will low if further changes

are made in speed. The speed is maintained at the level where dp/dw=0.

Fig:-Diagrammatic representation of Peak power tracking

System Control

Speed Control

The major reasons for the control of the rotor speed are as follows:-

· For the generation and storage of more energy

· For the protection of the rotor, the generator and power electronic equipment during high

wind which may cause overloading

· When the generator is disconnected accidentally or for any other purpose which loses

electrical load causing rotor speed runaway destroying it mechanically, so for the

protection of rotor speed control should be maintained.

The speed control of rotor comprises five regions which are:-

· The cut-in speed at which turbine starts producing power below which turning on turbine

is not efficient.

· The constant maximum Cp region where rotor speed varies with wind speed which varies

to operate at constant TSR corresponding to the maximum Cp value.

· During high wind rotor speed is limited to upper constant limit which constant speed

region Cp is lower than maximum Cp by which power is increased at low rate than in

first region.

· At still higher wind speed, machine is operated at constant power for the protection of

generator and other power electronic from overloading which is done by decreasing rotor

speed but causes generator overloading for which some sort of brake, eddy current or

other devices attached to the rotor.

Fig:- Regions of speed control phase

Rate Control

The large rotor inertia of blades by acceleration and deceleration must be controlled for avoiding

mechanical stress on rotor blades. The instantaneous difference in mechanical power produced

by blades and electrical power delivered by the generator will change the rotor speed as follows:-

Jdw/dt= (Pm-Pe)/w where,

J= polar moment of inertia of the rotor

W= angular speed of the rotor

Pm= mechanical power produced by the blades

Pe= electrical power delivered by the

The speed control strategy varies with the type of electrical machine used which are the

induction machine, the synchronous machine or the DC machine.

Environmental Aspects

The Environmental impact considered for the establishment of wind power generation plant in

small scale and huge scale consists of two environmental components which include:-

Bio-physical Environment

It includes biological components of the desired project areas and study is based on the aquatic

environment and water quality, noise, soils, terrestrial vegetation, terrestrial wildlife (including

birds).

Socio-Economic Environment

This is based on the effects on social life of habitants and their economic activities and the study

is based on cultural resources, planned land use, recreation, safety (including ice shedding),

social environment, visual landscape.

Wind power generation is environmental friendly energy source which includes tower

mechanism structure which fits in environment completely but yet brings effects such as noise

and other aesthetics for which advanced installation procedure are being adopted. The most

significant negative environmental issues relating to wind energy are noise, land area and use,

visual impacts and bird strike.

Noise

The noise is most considerable effect of wind energy which has two possible sources during its

operation noise production by the gearbox and aerodynamic noise from blades. The mechanical

noise from gearbox is optimized to zero by the help of modern construction and vibration control

whereas the aerodynamic noise which is generated from blades while passing through tower and

higher speed is controlled by better design processes such as smoothening and scratching of

blades. At present acceptable average noise from turbine is 45 dBA and 35dBA at distance of

250m or less for calm inhabited quarters and 40 dBA during day and 35 dBA in nighttime for the

building, public and other objects.

Impact on nature

The existing vegetation is removed from small area of construction also the temporary access is

disturbance for the fencing purpose. There is no significant changes on plants but should not

affect the conservation objective or any sites of national natural importance.

Impact on Birds

For the impact assessment ornithological impact assessment (OIA) impacts on birds should be

considered. There are three majors ways by wind project could effect on birds population:-

\Habitat loss: The constructed area may cause displacement of birds which are naturally habitat

around or feed in the construction site.

Collision: The magnitude of the collision rate must be considered which is given by background

of the mortality rate for the species and considered as negligible if increase of less than 1% on

mortality rate. The mostly effected birds consists of small nocturnal migrants, flying in large

numbers, especially at the condition of for or rain when there is poor flying condition they are

mostly suspected to strike to tall structures.

Disturbance: The impact of disturbance is considered if there is reduction of resources used by

the birds which reduces the carrying capacity.

Use of land

The problems of land use is experienced when there are other planned uses at the same location

since there are some design requirements of land such as the separation of turbines should be five

to ten tower heights which allows to reform wind strength and air turbulence by one rotor not

harm another turbine downwind also 1% of total area covered taken for the tower construction.

Conclusion

The destructive effects caused by wind energy are significant in compared to effect of use of

fossil fuel but there are some environmental effects by wind energy. For the sustainable

development EIA study is essential by which earlier inexact estimates can be compared

providing comprehensive and reliable results. The most ecological affect is impacts on birds for

which migratory lines should be preceded along with the correct decision for the site selection by

which biodiversity protection can maintained from the clean production from renewal source.

Reference

1. Mukund R. Patel (1999). Wind and Solar Power Systems. United States of America:

Boca Raton London New York Washington, D.C.. Ch 2,4,5.

2. Dan Chiras (2010). Advance Praise for WIND POWER Basics. 2nd ed. Canada : New

Society Publishers. 33-57.

3. Wei Tong (2010). Wind Power Generation and Wind Turbine Design. British Library

Cataloguing-in-Publication Data: WIT Press. 7-35.

4. Hugh Piggott (2000). Wind power Workshop. London: Centre for Alternative

Technology publication. 34-56.

i

i

OCEAN ENERGY:

Untapped Source of Potentially huge energy

Prepared by: AnushaAiri

Masters in Barents Environmental Engineering 1st

year

i

TABLE OF CONTENTS

TABLE OF CONTENTS I

1. INTRODUCTION 1

1.1 BACKGROUND 1

1.2 POTENTIAL 1

2. TYPES OF OCEAN ENERGY 1

2.1 WAVE ENERGY 1

2.2 TIDAL ENERGY 3

2.3 OCEAN THERMAL ENERGY 5

3. ADVANTAGES AND DISADVANTAGES OF OCEAN ENERGY 6

4. WAY FORWARD 7

5. REFERENCES SITED 7

1

1. Introduction

1.1 Background

Ocean energy is a form of renewable energy that uses the ocean's tides, waves, winds, currents and thermal elements

to generate energy. Oceans cover over 70% of the Earth’s surface, making them the world’s largest solar energy

collectors. The oceans constitute the largest powerhouse on Earth. There are three basic ways to tap the ocean for its

energy. We can use the ocean's waves (Ocean Wave Power), we can use the ocean's high and low tides (Ocean Tidal

Power), or we can use temperature differences in the water (Ocean Thermal Energy Conversion – OTEC).

1.2 Potential

Of all the emerging alternative technologies, ocean energy is perhaps the least advanced, but with great potential.

Some says that ocean energy is where wind was 20 years ago because ocean energy is currently undeveloped

compared to other conventional and renewable energy technologies.

Ocean energy is mostly in an experimental stage but some of its component technologies have the potential to

become mainstream energy sources and are now being trailed.Ocean tides constitute a clean and inexhaustible

energy source, free from the climatic irregularities which are a constraint on wind and solar power.Ocean energy is

preferable to wind because tides are constant and predictable and water’s natural density requires fewer turbines

than are needed to produce the same amount of wind power.

Ocean energy has the potential to deliver ten million terra-watt hours of electricity per year.One of the world’s most

suitable sites is the estuary of the river Rance, in western France, where the difference between high and low tides

averages 8.17 metres, peaking at 13.5 metres during the equinoxes.

2. Types of Ocean Energy

The ocean can produce two types of energy: thermal energy from the sun's heat, and mechanical energy from the

tides and waves.

2.1 Wave Energy

As stated earlier, wave energy is one of the two renewable energy sources which belong to the Ocean energy. Wave

energy is the energy carried by the waves on the surface of the ocean or sea, which can be captured and be used for

the production of electricity, water desalination and other useful activities. It must be stated that there is tremendous

energy in waves and thus this form of energy cannot be neglected.

In order for us to be able to capture wave energy, we need waves. How are the waves produced?Waves are produced

by wind blowing over the oceans. The wave duration, height, speed, the energy it contains and many other

parameters differ from region to region and ocean to ocean. In many regions the wind blows consistently, in strength

and duration, and this make wave energy predictable and thus more exploitable and marketable.

There are two basic ways we can trap wave energy using different wave power devices. The first way is trapping the

wave energy at the surface of the wave from essentially the surface motion of the waves and the second way is the

pressure fluctuations caused below the surface of the waves.

2

One important factor that one should have in mind is that wave energy is different than tidal energy. The energy a

wave carries is directly proportional to the square of its height and thus the waves generated in oceans are definitely

stronger and carry more energy than the ones generated in usually calm seas, like the Mediterranean Sea.

There various reasons why we consider tapping wave energy and using it as an alternative renewable green

energy.Some of these are:

· It is clean, renewable and environmentally friendly

· Waves are available to a lot of countries thus making wave energy a widely distributed renewable from of

energy

· Once waves are generated they travel great distances with little loss of energy

· Through the use of satellites, waves are anticipated 1-2 days in advance, thus they are predictable and this

enable electricity network operators to plan and manage usage

· Waves have a good seasonality and their existence coincides with the high demand seasons of various

regions of the world

· Waves are usually out of phase with their generating source, the wind, and given the fact that they travel

great distances, the two energy sources can be used to complement each other.

Wave Technologies:

There are various forms of wave technologies that have been developed

recently and/or improved recently so as to capture the power of the

waves in the most efficient way. First of all, we have to note that wave

capturing devices can be installed at one of the following 3

locations: nearshore, offshore and far offshore. Choosing the right

technology and the right type of location is done under a careful techno-

economic evaluation.

Four different types of wave energy capturing deviceshave been

identified.Although all of them are installed at the surface or near the

surface of the ocean they differ in the way they interact with the waves,

capture the wave energy and the way they convert this energy into

electricity. These four technologies are:

Terminator devices:

These devices are installed to extend perpendicular to the way the wave travels and capture the wave energy by

‘’reflection’’. These devices started as near shore devices but their recent developments have enabled them to be

installed offshore and sometimes far offshore.

Point absorbers:

Point absorbers are floating structures that are installed on the surface of the sea and move with the wave motion

and relative to each other. This relative motion is converted into energy through the use of electromechanical or

hydraulic energy converters.

Attenuators:

These are long floating structures installed parallel to the direction of the wave, the different height of the waves

causes them to be flexed and this drives hydraulic energy converters and thus captures the wave energy.

Overtopping devices:

Picture layout showing the wave energy

technologies in the ocean

3

These devices are essentially reservoirs that get full with the waves and when the water is emptied, the power due to

gravity drives hydro turbines the same way as the hydroelectricity is produced.

Environmental Implications:

There are some environmental issues in the case of wave energy that may need to be addressed. These are issues

with possible pollution from the technologies used and the disturbance of the sea life in the vicinity of these

technologies. Any wave energy project needs to address these issues and handle them adequately.

Wave energy is a renewable green energy that has a lot to give to mankind and we believe that it is still at the stage of

infancy. Wave energy technologies need to mature and become more cost effective is wave energy is to be fully

exploited and we believe that wave energy has a lot to offer.

2.2 Tidal Energy

Tidal energy is one of the oldest forms of energy

used by humans. Indeed, tide mills, in use on the

Spanish, French and British coasts, date back to 787

A.D. Tide mills consisted of a storage pond, filled by

the incoming (flood) tide through a sluice and

emptied during the outgoing (ebb) tide through a

water wheel. The tides turned waterwheels,

producing mechanical power to mill grain. We even

have one remaining in New York- which worked well

into the 20th century.

Tidal power is non-polluting, reliable and

predictable.Tidal barrages, undersea tidal turbines -

like wind turbines but driven by the sea - and a

variety of machines harnessing undersea currents

are under development. Unlike wind and waves,

tidal currents are entirely predictable.

The demand for electricity on an electrical grid

varies with the time of day. The supply of electricity

from a tidal power plant will never match the

demand on a system. But, due to the lunar cycle and

gravity, tidal currents, although variable, are reliable and predictable and their power can make a valuable

contribution to an electrical system which has a variety of sources. Tidal electricity can be used to displace electricity

which would otherwise be generated by fossil fuel (coal, oil, natural gas) fired power plants, thus reducing emissions

of greenhouse and acid gasses.

Tidal energy can be harnessed in two ways:

· By building semi-permeable barrages across estuaries with a high tidal range.

· By harnessing offshore tidal streams.

Barrages allow tidal waters to fill an estuary via sluices and to empty through turbines. Tidal streams can be harnessed

using offshore underwater devices similar to wind turbines.

Picture of Tidal energy conversion process

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Most modern tidal concepts employ a dam approach with hydraulic turbines. A drawback of tidal power is its low

capacity factor, and it misses peak demand times because of 12.5 hour cycle of the tides. The total world potential for

ocean tidal power has been estimated at 64,000 MWe. The 25-30 feet tidal variations of Passamaquoddy Bay (Bay of

Fundy) have the potential of between 800 to 14,000 MWe.

Good areas for exploiting tidal energy

Tidal range may vary over a wide range (4.5-12.4 m) from site to site. A tidal range of at least 7 m is required for

economical operation and for sufficient head of water for the turbines. Traditional tidal electricity generation involves

the construction of a barrage across an estuary to block the incoming and outgoing tide. The dam includes a sluice

that is opened to allow the tide to flow into the basin; the sluice is then closed, and as the sea level drops, the head of

water (elevated water in the basin) using traditional hydropower technology, drives turbines to generate electricity.

Barrages can be designed to generate electricity on the ebb side, or flood side, or both.

Tidal range may vary over a wide range (4.5-12.4 m) from site to site. A tidal range of at least 7 m is required for

economical operation and for sufficient head of water for the turbines. A 240 MWe facility has operated in France

since 1966, 20 MWe in Canada since 1984, and a number of stations in China since 1977, totaling 5 mWw. Tidal energy

schemes are characterised by low capacity factors, usually in the range of 20-35%.

Currently, although the technology required to harness tidal energy is well established, tidal power is expensive, and

there is only one major tidal generating station in operation. This is a 240 megawatt (1 megawatt = 1 MW = 1 million

watts) at the mouth of the La Rance river estuary on the northern coast of France (a large coal or nuclear power plant

generates about 1,000 MW of electricity). The La Rance generating station has been in operation since 1966 and has

been a very reliable source of electricity for France. Elsewhere there is a 20 MW experimental facility at Annapolis

Royal in Nova Scotia, and a 0.4 MW tidal power plant near Murmansk in Russia. UK has several proposals underway.

Studies have been undertaken to examine the potential of several other tidal power sites worldwide. It has been

estimated that a barrage across the Severn River in western England could supply as much as 10% of the country's

electricity needs (12 GW). Similarly, several sites in the Bay of Fundy, Cook Inlet in Alaska, and the White Sea in Russia

have been found to have the potential to generate large amounts of electricity.

Environmental Impacts

Tidal energy is a renewable source of electricity which does not result in the emission of gases responsible for global

warming or acid rain associated with fossil fuel generated electricity. Use of tidal energy could also decrease the need

for nuclear power, with its associated radiation risks. Changing tidal flows by damming a bay or estuary could,

however, result in negative impacts on aquatic and shoreline ecosystems, as well as navigation and recreation.

The few studies that have been undertaken to date to identify the environmental impacts of a tidal power scheme

have determined that each specific site is different and the impacts depend greatly upon local geography. Local tides

changed only slightly due to the La Rance barrage, and the environmental impact has been negligible, but this may not

be the case for all other sites. It has been estimated that in the Bay of Fundy, tidal power plants could decrease local

tides by 15 cm. This does not seem like much when one considers that natural variations such as winds can change the

level of the tides by several metres.

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2.3 Ocean thermal energy

Ocean thermal energy is used for many applications, including electricity generation. There are three types of

electricity conversion systems: closed-cycle, open-cycle,and hybrid. Closed-cycle systems use the ocean's warm

surface water to vaporize a working fluid, which has a low-boiling point, such as ammonia. The vapour expands and

turns a turbine. The turbine then activates a

generator to produce electricity. Open-cycle

systems actually boil the seawater by operating

at low pressures. This produces steam that

passes through a turbine/generator. And hybrid

systems combine both closed-cycle and open-

cycle systems.

The idea is not new. Using the temperature of

water to make energy actually dates back to

1881 when a French Engineer by the name of

Jacques D'Arsonval first thought of OTEC. The

final ocean energy idea uses temperature

differences in the ocean. It's warmer on the

surface because sunlight warms the water. But

below the surface, the ocean gets very cold.

Power plants can be built that use this

difference in temperature to make energy. A difference of at least 38 degrees Fahrenheit is needed between the

warmer surface water and the colder deep ocean water.Using this type of energy source is called Ocean Thermal

Energy Conversion or OTEC.

Ocean Thermal Energy Conversion Technologies

There are three kinds of OTEC systems: closed-cycle, open-cycle, and hybrid.

Closed-Cycle

Closed-cycle systems use fluids with a low boiling point, such as ammonia, to rotate a turbine to generate electricity.

Warm surface seawater is pumped through a heat exchanger, where the low-boiling-point fluid is vaporized. The

expanding vapour turns the turbo-generator. Cold deep seawater—which is pumped through a second heat

exchanger—then condenses the vapour back into a liquid that is then recycled through the system.

In 1979, the Natural Energy Laboratory and several private-sector partners developed the mini OTEC experiment,

which achieved the first successful at-sea production of net electrical power from closed-cycle OTEC. The mini OTEC

vessel was moored 1.5 miles (2.4 km) off the Hawaiian coast and produced enough net electricity to illuminate the

ship's light bulbs and run its computers and televisions.In 1999, the Natural Energy Laboratory tested a 250-kW pilot

OTEC closed-cycle plant, the largest such plant ever put into operation.

Open-Cycle

Open-cycle systems use the tropical oceans' warm surface water to make electricity. When warm seawater is placed in

a low-pressure container, it boils. The expanding steam drives a low-pressure turbine attached to an electrical

Picture depicting Ocean thermal energy conversion process

6

generator. The steam, which has left its salt behind in the low-pressure container, is almost pure, fresh water. It is

condensed back into a liquid by exposure to cold temperatures from deep-ocean water.

In 1984, the Solar Energy Research Institute (now the National Renewable Energy Laboratory) developed a vertical-

spout evaporator to convert warm seawater into low-pressure steam for open-cycle plants. Energy conversion

efficiencies as high as 97% were achieved. In May 1993, an open-cycle OTEC plant at Keahole Point, Hawaii, produced

50,000 watts of electricity during a net power-producing experiment.

Hybrid

Hybrid systems combine the features of closed- and open-cycle systems. In a hybrid system, warm seawater enters a

vacuum chamber, where it is flash-evaporated into steam, similar to the open-cycle evaporation process. The steam

vaporizes a low-boiling-point fluid (in a closed-cycle loop) that drives a turbine to produce electricity.

Environmental and Economic Challenges

In general, careful site selection is key to keeping the environmental effects of OTEC minimal. OTEC experts believe

that appropriate spacing of plants throughout tropical oceans can nearly eliminate any potential negative effects on

ocean temperatures and marine life.

OTEC power plants require substantial capital investment upfront. OTEC researchers believe private sector firms

probably will be unwilling to make the enormous initial investment required to build large-scale plants until the price

of fossil fuels increases dramatically or national governments provide financial incentives. Another factor hindering

the commercialization of OTEC is that there are only a few hundred land-based sites in the tropics where deep-ocean

water is close enough to shore to make OTEC plants feasible.

Lastly, Ocean mechanical energy is quite different from ocean thermal energy. Even though the sun affects all ocean

activity, tides are driven primarily by the gravitational pull of the moon, and waves are driven primarily by the winds.

As a result, tides and waves are intermittent sources of energy, while ocean thermal energy is fairly constant. Also,

unlike thermal energy, the electricity conversion of both tidal and wave energy usually involves mechanical devices.

3. Advantages and Disadvantages of Ocean Energy

Advantages

· It is a renewable Energy Source

· It is available abundantly

· Tides/Waves are always predictable and so are their power

· Production of a significant amount of energy

· Waves are free and will not run out so the cost is in building the power station

· Clean technology since it doesn’t produce greenhouse gases

Disadvantages

· Harnessing the power of it is difficult

· It can cost a lot of money and requires further research

· If the whole tidal/wave energy scheme does get popular real estate will be losing money for beach front

houses since they will be using the beaches for the tidal/wind farms.

· May interfere with mooring and anchorage lines commercial and sport fishing

· Waves can be big or small so efficiency of the technology is likely to alter

· Transport of the electricity from the sea onto the land is necessary

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· Initial installations and other setup can be really expensive since not many people have tried to generate

electricity this way

· It is believed that harnessing wave or tidal power will eventually slow the rotation speed of the planet. It is

currently believed that we could cause as much as a full day of loss to our calendars every two thousand years

by collecting enough energy from waves and tides

4. Way Forward

The Ocean energy is likely to offer long-term carbon emissions reduction but the installation of this technology is

unlikely till 2020 due to its early stage of development. All ocean energy technologies, except tidal barrages, are

conceptual, undergoing research and development (R&D), or are in the pre-commercial prototype and demonstration

stage. The performance of ocean energy technologies is anticipated to improve steadily over time as experience is

gained and new technologies are able to access poorer quality resources. Whether these technical advances lead to

sufficient associated cost reductions to enable broad-scale deployment of ocean energy is the most critical uncertainty

in assessing the future role of ocean energy in mitigating climate change. Though technical potential is not anticipated

to be a primary global barrier to ocean energy deployment, resource characteristics will require that local

communities in the future select among multiple available ocean technologies to suit local resource conditions.

5. References sited

· http://wiki.answers.com/Q/What_are_the_advantages_and_disadvantages_of_using_the_energy_from_ocean

_waves#ixzz2B4LA7QCh

· http://interestingenergyfacts.blogspot.fi/2008/03/ocean-energy-facts.html

· http://www.renewableenergyworld.com/rea/tech/ocean-energy

· http://www.fossil.energy.gov/education/OceanEnergyMMS.pdf

· Front cover photo: http://penbay.org/audio/ff09/ff09_oceanenergy.html

· http://www.renewablegreenenergypower.com/introduction-to-wave-energy/

· http://www.oceanenergycouncil.com/index.php/Tidal-Energy/Tidal-Energy.html

· http://www.google.fi/imgres?imgurl=http://technologystudent.com/images5/tidal1.gif&imgrefurl=h

ttp://technologystudent.com/energy1/tidal1.htm&h=500&w=500&sz=26&tbnid=Scz5o7R16yzuNM:

&tbnh=90&tbnw=90&zoom=1&usg=__Jv0p_NDJtHGIeJ00GWBWfa9PJKk=&docid=wnFFKNuZQE8djM

&sa=X&ei=ZS2VUJ-aJaPk4QTp6oCYAQ&ved=0CC4Q9QEwAw&dur=2724

· http://www.eere.energy.gov/basics/renewable_energy/ocean_thermal_energy_conv.html