Unit 9 EXPLOITATION TECHNOLOGIES OF THE ENERGY POTENTIAL ... 9.pdf · U 9: Exploitation...

U 9: Exploitation technologies of the energy potential of sea waves

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Unit 9

EXPLOITATION TECHNOLOGIES OF THE ENERGY POTENTIAL OF SEA

WAVES

Unit 9.1

Exploitation technologies of the energy potential of sea waves

Recommended study rate: 100 min.

Contents

General considerations. The energy of the Planetary Ocean waters

Wave energy.

Wave energy captation systems.

UNIT 9.1.OBJECTIVES

- to identify and characterize the major renewable energy potential and recovery of sea

waves.

- to characterize the specific theoretical elements of wave energy;

- to identify the types and characteristics of waves energy captation systems.

9.1 General considerations. The energy of the Planetary Ocean waters

In the last century, the energy from fossil fuels (oil, gas, coal) by combustion has had

disastrous effects on the environment, greater than any human activity in history: the

accumulation of greenhouse gases in the atmosphere, which triggered irreversible processes,

such as ozone depletion, global warming etc. Therefore, the use of alternative energy sources

becomes increasingly important, even more necessary for today's world. These sources, such

as sun, wind, geothermal, etc. are practically inexhaustible and are called renewable energy,

also known as alternative or unconventional.

As we have seen in Chapter 7 renewable energy is mainly based on the great nuclear

fusion reactor which is the Sun. Tide, is based on the kinetic energy of the Moon, which by its

gravity generate the tides and geothermal energy is based on the hot core of the earth,

remained since its creation.

All renewable energies produce far fewer emissions, reduce chemical pollution,

thermal radiation and are available anywhere around the globe.

The rapid depletion of fossil fuels reserves, their use being accompanied by

environmental pollution (including the so-called ”dirty heat”, and an alarming increase in

proportions of the level of carbon dioxide in the atmosphere), the limited resources of

uranium ( by using it energetically we get radioactive waste) and the uncertainty of life and

the ecological consequences of the industrial use of thermonuclear energy make researchers,

scientists and engineers pay more attention to seeking new opportunities for alternative,

unlimite d clean and profitable energy sources.

Among the most effective alternative or unconventional energies, the World Ocean

waters (waves, ocean currents, wave and hydro power)are considered to be very important.

Oceans and seas occupy 71% of the Earth's surface and, in addition, have an inexhaustible

resource: waves. The energy of seas and oceans is in the form of mechanical energy and heat.

Ocean waters have a huge energy potential which can be revaluated for electricity generation,

since the energy reserves of the Ocean are huge.


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The internal energy, corresponding to a 20°C warming of the surface of ocean water,

compared to the river, has a size of about 1026

J. The kinetic energy of ocean currents is

approximately equal to 1018

J, but this energy can only be used in a tiny amount. The main

energy sources considered, at least in the current technique, refer to: tides, sea currents,

waves, temperature differences of sea water layers.

● Tides, due the Moon attraction, regularly occur in some coastal areas of the world, with

amplitudes that can sometimes reach 14-18 m causing slow oscillations of the level of marine

waters. The principle of using tidal energy in the tidal power plants, consists in building

dammed pools to make possible the caption of water energy, triggered by these oscillations, at

filling (the flow) and the drain (at ebb). Tide is the energy that can be captured by exploiting

the potential energy from the vertical movement of the water mass at different levels or

kinetic energy due to tidal currents. Tidal energy comes from the gravitational forces of the

Sun and the Moon, and as a result of terrestrial rotation. To make tidal energy more efficient

certain natural conditions are needed:

- a natural pool (usually an estuary) to communicate with the ocean through a narrow

opening;

- amplitude tides to be of at least 8 m These natural conditions occur only in about 20 parts of

the world (the Atlantic coast of France, Great Britain, USA, Canada, northern Australia,

eastern China, etc..). If it could be fully exploited within tidal power plants, the amount of

available energy would produce about 100,000 times more energy than all hydropower

currently in operation worldwide (other calculations considers that given the annual tide

energy could amount to that obtained by the burning of more than 70, 000 tons of coal). But

tidal power plants produce a kWh cost price twice higher than that obtained in hydro power

plants. Currently in operation, such tidal power plants are located in:

- France: the Rance estuary, formed by the river with the same name at the mouth of the Gulf

of Saint Malo, built between 1961-1966 with a capacity of 240 MW, the "Chausey" provides

a similar construction in the Bay of Le Mont Saint Michel.

- Russia in Kislaya estuary formed by the rivers and Tuloma and Kola at the Barents Sea,

with a capacity of 400 MW, another project aimed at the White Sea shores).

- Other projects provide new facilities on the southeastern coast of Great Britain, on the

shores of Bay of Fundy, where the U.S. and Canada conducted a large-scale construction.

● Sea currents which can consist of:

- Horizontal currents (due to prevailing winds);

- Vertical currents (where the water goes up or down from/to the deep)

Water movement owe sea currents of the planet, are the bearers of very high kinetic energy.

The literature shows that a wide ocean current of about 100 m, 10 m depth and a speed of 1 m

/ s, could generate for one year a kinetic energy of about 2 million kWh.

● Waves are a form of energy storage provided by wind energy calculable and considered

worthy. Wave motion is due to increasing solar radiation. The calculations have shown that

waves with a height of 1 m, a length of 40 m and for a period of 5 seconds have a power of

around 5 kW along a frontline of 1 m in width. Numerous hydraulic and energy research

institutes in the U.S., France, Britain, China and Japan have included in their work program

the construction of installations for the capture of wave energy. Yet, judging by the huge

potential offered by the seas and oceans, wave energy is insufficiently exploited.

● Ocean-thermal energy conversion, consists of electrical energy obtained due to the

difference in temperature between the surface water and the groundwater. The thermal


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potential can be realized through heat pumps. The differences in temperature of sea water

structures create thermal heat - stored as heat. The amount of heat that can be revaluated

corresponds to a voltage difference (between the surface and depth waters) from a few

degrees to 30 ° C.

● A longer perspective is to obtain power based on the differences in the salinity of salt water

and freshwater (this phenomenon is present at the mouth of the Danube overflowing into the

Black Sea).

Homework 9.1: Identify the main revaluation opportunities of the wave energy

potential for the Black Sea coast.

9.2. Wave energy

Waves are rhythmic movements of water particles around an imaginary point of

equilibrium. From a phenomenological point of view, we known: wind, tidal, anomobaric,

marine, stationary, gravity free, or forced by the wind waves. Wind waves are occurring under

the action of tangential friction in the movement of air masses.

Wave formation has several theories, the most sustainable theory being that of

trohoidal waves (trochoid – a curve described by a point in a circle moving on a flat surface,

trochoidal waves) of Gerstner (1802) (Gerstner wave model is a perfect model, assuming a

certain time wave form). In addition to trohoidal waves, the literature uses other models as

well: Stokes-type waves, conoidal waves, etc.. Gerstner's theory is developed for an ideal

liquid of volume of unlimited depth, a frictionless liquid with constant density, in which

translational or free gravity motion waves shape up.

The conclusions of this theory are that the particles of water in their movements follow

a closed orbit in an interval equal to the wave orbit which is slightly distorted by the wave and

the particles from the surface receive the largest amount of wind, so they have the largest

orbital radius.

With increasing depth, hydraulic energy is transmitted, so the particle orbits are

dwindling. Waves have potential energy Ep, and kinetic energy Ec, calculated in light of the

wave size and speed. The wave with ideal symmetrical shape is the regular crestless wave,

which is a gravitational dying-down wave, unforced by the wind. As this energy is manifested

in the interval equal to the period T of the wave, the power P will be equal to the ratio

between the energy Ep and Ec and the time T. Because the capture processes currently take

only one of two forms of energy wave, the term available gross power is presented in the

relation:

2K h L

PT

(9.1)


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Fig. 9.1 Wave profile: h = height; λ =wavelength; L =the lenght of the wave frontline

With the ratio λ/T which expresses the propagation speed of the wave, called celerity

(celerity n.f. – obs. 1. Speed, rapidity.. 2. propagation speed of the wave, a disturbance in a

fluid medium at rest. - from fr. célérité, lat. celeritas,- atis.) denoted by c:

cT

(9.2)

the expression for power can be written in the form:

2P K h L c (9.3)

Literature suggests in a simplified form suitable for a the coefficient K, a fixed value

K = 1/16 (K factor in other works, takes into account the water depth in which the wave

propagates). Adopting the value of Black Sea water with a specific weight, γ = 9986.58 N/m³,

the power developed on each meter of wave front is:

2P 975 h L c , W/m (9.4)

Of course not all raw energy can be captured on the front line systems respectively.

Some energy is reflected in contact with captators, another is dissipated in the watersheds of

hydropower and marine captation power plants, and some managed to cross the sealing area.

Considering that a facility is able to capture the largest possible amount of energy stored in

waves, namely that the overall captation efficiency, η, is higher, it demonstrates its economic

efficiency. The captured energy, E, is obtained from the relationship:

PE E (9.5)

The wave height is the distance measured vertically from the wave crest and the lower

line rate corresponding to a next wave base. The wave height is determined by means of

special apparatus and the values are given in meters or feet. The regular ocean wave height is

5 m and the maximum values measured so far are:

- 21 m in the northern Pacific basin;

- 15.6 m in the northern Atlantic basin;

- 14 m in the southern hemisphere;

- 11.5 m in the Indian Ocean.

The wave length is the distance in meters or feet measured horizontally between two

successive ridges or grooves of a wave. The mean values of ocean waves are between 69 m

and 110 m. The maximum wave length values are determined on the basis of numerous

observations and they are the following:

- 170 m in the northern Atlantic basin;

- 214 m in the southern basin of the same ocean;

- 233 m in the Pacific Ocean;

- 342 m in the southern Indian Ocean basin.


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The maximum dimensions of waves are noticed in regions where the wind speed,

duration and area of free development of waves are highest. Throughout the Planetary Ocean

the highest frequency waves have short height, 2.1 m below the exceptional case of extreme

events when they may have heights of 20 meters and a length of about 400 m and during

hurricanes the common height is of about 8 m, within over 8 seconds, at a speed of 18-20 m /

s and a slope of about 1/10 - 1/30 m in regions with frequent hurricanes and dangerous for

navigation that coincide with cyclone genesis regions, as the northern parts of the Pacific

Ocean, the Atlantic Ocean and hurricanes(typhoons) in the tropical regions. The highest

frequency of hurricanes is observed during the end of winter (February) and thr end of

summer (August).

When the waves reach the bottoms of the right lower ribs spread phenomenon called

surging occurs. By surging we mean the lifting, bending forward, bending and collapse of the

ridge, with noise. If surging occurs above a remote coastal waves of this kind are called

"disruptive". Relief of wind waves in the ports is obtained by spreading a limited quantity of

oil to the surface. This process stops the orbitoidal movement of water particles on the

surface, a process that the interference is transmitted and depth. Similar effects resulting from

the coverage of large areas with ice floes, or the development of aquatic vegetation on large

areas.

Raindrops also calm down the waves, especially during intense rainfall, with high

energy. Wave energy is really limitless, as a wellspring, as it is as inexhaustible as the ocean.

In shallow seas, enclosed on all sides by land, as, for example the Black Sea, the wave height

rarely exceeds four or five meters, while in the open ocean, especially in the southern

hemisphere, which includes water circle the globe and waves can unleash at will and the west

winds blow continuously without change of course, often meet waves of 12-18 m in height.

The colossal wave energy is manifested in the striking force, which has extremely high

values.

The full use of wave energy is hampered by the fact that this source of energy is very

uneven. In this context, wave energy can be used only if the waves are high and constant over

time. Contemporary technique does not know at this point, any systems through which wave

energy can be converted easily, completely and and economically into energy.

Homework 9.2: Identify with the help of internet resources the main characteristics of

waves in the Romanian Black Sea area.


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9.3. Captation systems of wave energy

The first that ever began using wave energy were the Europeans (Scotland, Portugal

and the UK have special programs for the waves surrounding the shores to be used for

energy). The basic concept to get electricity from water flowing through a turbine rotor is well

established for dedicated applications in hydroenergetic power (rivers and streams of water)

and wind power. Two main groups of technologies were invented to produce electricity from

wave energy: near-shore devices (easily accessible, easier to maintain and monitor) and

devices in high seas (offshore and large depths, produce the largest amount of energy). In the

short term, until technology advances, devices near the coastline can be used mainly due to

their easy accessibility. For long term offshore devices will be used extensively due to the

amount of energy obtained (but only if they will find a technology that can facilitate their

access and maintenance).

Devices near the shores are generally fixed directly on the ocean floor that is not too

deep and are connected to the shore or in the immediate vicinity of the latter. One of the first

systems that exploit wave energy device is placed on the Scottish island of Islay, which uses

the concept of technological oscillatory water column (Ocillating Water Column - OWC)

proposed by the company Wavegen Limpet. OWC wave motion capture technology allows

seas/oceans as they push a cushion of air up and down behind a breakwater. The Wells

Turbine inside generates electricity from rotation in the same direction, whether the air is

moving up or down.

We know more wave energy capture systems, including:

1. Pressure piping (is like a vehicle braking system). Thus the pressure exerted on a

large surface is transmitted through a liquid pipeline, to a smaller area, thus multiplying the

force per unit area. Through a mechanical system, this power triggers the operation of the

electric generator. This principle is applied by Interproject Service (IPS) Buoy (Sweden)

http://members.tripod.com/interproject - Archimedes Wave Swing (Netherlands)

www.waveswing.com - Ocean Power Delivery (Scotland) www.oceanpd.com - Energetech

(Australia) www.energetech.com.au

2. System based on liquid ascent. The system relies on water ascent as a wave on an

artificial slope, which is then taken up by the blades of an electric generator. The idea was

implemented by Wave Dragon (Denmark) www.wavedragon.net

3. The liquid piston system. In an enclosure, it's a movement of ascent and descent, the

marine wave acts as a piston, pumping and aspiring air, a direct result of a turbine (in many

applications using the Wells turbine). Wavegen (Scotland) www.wavegen.co.uk and Mighty

Whale (Japan) www.jamstec.go.jp have implemented such projects. In a simple scheme,

floating systems go up and down with the passing waves. By this movement pump is driven

that pushes water from a turbine which acts as a generator.

Scotland has access to one of the richest marine energy resources in the world. If in

2001, Scotland's Renewable Resource report showed that Scotland generated a capacity of up

to 21.5 GW (79.2 TWh/year) with the energy of waves and tides, in 2010 the Scottish

Government was funding over four million pounds for the largest offshore energy farm in the

world, providing up to 10% of the country's necessary amount of energy. According to the

report Harnessing Scotland's Marine Energy Potential performed by Marine Energy Group in

http://www.energetech.com.au/


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2020 in Scottish waters can be installed capacities of 1300 MW, 100 MW by adding 100 MW

each year.

In northern Scotland (Nigga), Scottish experts thought of a special platform to use the

most power from waves without mounting floating hydroelectric generators (the Oyster

project, a very promising invention, fig.9.2).

Fig. 9.2 OYSTER Platform, 300- 600 kW

The platform is a component mounted in water, which toggles when hit by huge waves. To

this aim it is fitted with two pistons that push compression speed water through a pipe to an

establishment in the vicinity. There, water pressure triggers a series of blades, all the

mechanism is identical to the one that is used in hydropower plants.

All the difference lies in the innovative ways to carry water under pressure. The

manufacturers say that Oyster can generate between 300 and 600 kW, but in multiple

configurations, can reach values large enough to power the nearby towns. It is hoped that new

industry would revitalize the Scottish economy, especially in rural areas and create over 7,000

jobs in various collateral fields involved. Another experimental scheme to use wave energy is

achieved for Islay Island, off the coast of western Scotland, is designed to generate 180 kW. It

works on the principle of the oscillating water column.

.

Fig. 9.3 The power production system devised by SDE Energy Ltd.

A submerged room, opened at the lower bottom, contains a column of air above. With

the passing waves, the water column rises and falls, pushing and pulling air out of a turbine

connected to an electric generator. SDE Energy Ltd. uses equipment by generating hydraulic

pressure due to the movement of waves, generating electricity thereby.


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The operating principle is simple: a few rafts go up and down with the passing waves,

this movement is driven by a pump that pushes water through a turbine which drives a

generator, fig.9.3.

The Wells turbine for wave energy capture, was invented in 1980 by Professor Alan

Wells of Queen University in Belfast. Wells turbine, Fig. 9.4, is mainly used in power plants

exploiting wave energy, with some drawbacks that make the technology hardly feasible.

Efficiency is very low and under a low air current the turbine locks itself; the turbine blades

have a dash attack which is very large and a low seating angle, resulting in the need to use

these blades in both directions of operation of the air.

Fig. 9.4 Wells Turbine

In 1995, the Chinese from Guangzhou Institute of Energy Conversion built a

navigation buoy of 60 W using the Wells turbine. The most impressive applications of the

Wells turbine have been put in place in India where wave energy brings 1.1 MW to the

electrical system. A pilot plant was built in Romania, near the breakwater at Mangalia. The

system consists of a bottomless cylinder with a diameter of 1.5 m and a 2.5 m height.

By 2009 Portugal had installed 28 plants that produce a quantity of energy of 72.5

MW. In this sense, the first generator into operation is five kilometers from the shore, where

the Pelamis-type device was installed (the old name of a sea serpent), mounted in Peniche,

fig.9.5. Pelamis is an object that floats on the waves and performs a movement with an

elliptical trajectory. The simplest form of exploitation of this movement for wave energy

recovery are articulated pontoons. A modern building of this type is Pelamis which consists of

several articulated cylinders that, under the action of waves have relative movement acting

like pistons. Pistons pump oil under pressure through hydraulic motors operating as

generators, Fig. 9.6. The construction is floating on the sea surface, where it captures wave

energy and sends the current to Aguacadoura beach, north of Porto. It should be noted that a

single generator can provide electricity for 5000 households. In areas with waves all year

round or on the high seas and ocean, wave energy is a form of renewable energy with great

potential. Orecon company has invested over $ 24 million in a device, which is a combination

of beacon/maritime platform (equipped with special pressure chamber), the force of waves

hitting the platform is converted into electricity by a turbine. By 2015 we will see the first

platform that will provide electricity power distribution networks, producing about 1.5 MW.

One advantage is the platform size, being less prone to destruction and with lower

maintenance costs, fig.9.6.


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Fig. 9.5 Pelamis System(Peniche, Portugal) Fig.9.6 Maritime Platform Orecon

The inclined plane and storage tank system. In mid 1940s near Algiers in the

Mediterranean the first modern facility that consists of a structure designed on this principle

was put into operation in two experimental sites at Sidi Ferruch and Pointe Pascade. The

solution is based on the fact that in contact with a rigid construction, under the action of

waves, water tends to raise above the free surface.

This is received in an inclined slightly curved structure, which opposes the forward

direction of the wave front. The amount of water reaching between two convergent walls,

rises to a maximum height of the wave, then spilling into a tank designed to retain water at a

rate higher than the average sea level. The fall being achieved, the retained water moves the

turbines that in turn drive the electric generators. Convergence curves in the walls are required

bt the optimum hydraulic shapes that make the entire structure have a greatest possible

difference between the average sea level and the maximum water level in the storage tank,

fig.9.7.

.

Fig. 9.7 Sistemul cu plan înclinat şi bazin

The heavy-duty pier and liquid piston system

The whole capture structure-system consists of a heavy-duty pier through which runs a pipe

with water flowing variably, driven by waves, compressing and aspiring air above it in a

compartment located on a well-anchored floating device or fixed to a rigid foundation.

The liquid piston moves a limited amount of air, that activates the rotor turbine coupled to the

electric generator. The wave energy recovery can be done using schemes similar to those of

tidal power plants with a dam. Due to the short period of waves these schemes are less

efficient. The valve assembly, and the managing device, require optimal air flow recovery.

The pier should be constructed so as to remain as immobile in the turbulent wave mass,

fig.9.8.


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Fig. 9.8 Heavy-duty pier and liquid piston system Fig.9.9 System with floating device and damper valve

Any oscillation of the pier unnecessarily consumes the wind energy stored in the sea

or the ocean. The solution was tested at sea and gave the best results in sites with waves

whose average height ranged between 2 and 4 m, with an output estimated at between 30 and

70%. For a turbine diameter of 200 mm, made from an aluminum alloy, the nominal power

was 60 W and the duration of operation was estimated at more than three years (1960 meant

the exploitation of the first beacon and light buoys in the Sea of Japan, supplied with

electricity from the waves, and later, based on a patent issued in 1967 on behalf of Ryakusei

Kaisha, and it was still here that were low-capacity marine hydro-power plants were made

using the solution of the "liquid piston".

System with floting device and damper valve

Basically the structure consists of a floating device supporting a vertical column where

a damper valve is placed. It is designed so as to close halfway the wave length of a cycle,

forcing water from the pipeline to follow the movement of the floating device.

Fig. 9.10 System with wave-driven piston and interior hydraulic accumulator

When changing the direction of movement of the float, water continues to rise under

inertia, to a higher wave height. The sequence cycles increases the height of the water column

until it reaches the required pressure for the activation of the turbo-generator (an experiment

was made with an installation measuring 90 m in length, with a column diameter of 4.5 m, the

average wave height of 2.4 m, the capture and conversion system have achieved an output of

300 kW).


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Wave-driven piston system

The solution is to transmit the mechanical force given by a large amount of waves of

low pressure through a system of two pistons of different diameters, a small volume of

auxiliary liquid, which raises the pressure, causing its storage inside hydraulic accumulator,

fig .9.10. In various parts of the world other facilities were designed for the recovery of wave

energy, facilities that have been studied in the laboratory and in nature over the years, with

not always the most spectacular results.

Romanian specialists forecast that gross energy potential of waves on the 200 km of

the Romanian Black Sea coast amounts at about 8·109 kWh/ year, a technically usable energy

potential is estimated at 4·109 kWh/year, which would lead to a conventional fuel economy of

around 2 million t/year. Characteristic features associated with waves, currents and wind are

presented in Fig. 9.11. The studies carried out (even without their funding) have concluded

the necessity of wind and wave energy capture and have prompted some experts to continue

deepening the problem.

Figure 9.11. Height of significant wave Hs: black- wave; white – wind; red – current.


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The capture process is specifically designed and irregular waves are directly taken through a

floating vertical movement of water flow without transport - Figure

9.12.

Fig. 9.11 The Romanian system of exploitation of energy potential of waves in the Black Sea: 1 –

photovoltaic panel, 2 - wind turbine, 3 - rotary pneumatic motor, 4 - air reservoir, 5 - pneumatic, 6 - rectiliniar

generator 7 - lifting devices, 8 - DC generator, 9 - mobile, 10 – lock device, 11 - joint, 12 – anorage ears, 13 -

blockout 14 – floating device

The transmission of movement is performed using a linear generator (whose flux is

made so as to vary). Thus, this movement is converted into alternating current, with irregular

frequency, which can be used raw as a source of heat. The hydraulic equipment of a capture

element consists of a floating device, which takes in the irregular waves (with a height

between 50 mm and 9 m) and the main electrical equipment (consisting of a mobile part

connected with joints to the floating device and the fixed part, united with the stationary

structure). The solution required the creation of a stable floating structure in the turbulent

wave mass able to sustain the electric equipment. A special feature is the possibility of

developing unlimited vertical installation and the ability of the individual elements.

To compare the types of alternative energy, Professor Mark Jacobson of Stanford

University has calculated the impact they would have if the U.S. would be fed only on one

type of energy. He took into account not only the quantity of greenhouse gases that would be

emitted, but also the impact it would have on the ecosystem (the area occupied by land and

the water pollution). "The best alternative energies are not those spoken of the most"

concluded Jacobson.

Production and consumption of energy put considerable pressure on the environment:

climate change, damage to natural ecosystems, etc.. The energy activity is responsible for the

existence of pollutants in excess of 50% for emissions of methane and carbon monoxide, 97%

for sulfur dioxide emissions, 88% for nitrogen oxide emissions and 99% for carbon dioxide

emissions.

Ocean waters have a huge energy potential which can be used for energy. The main

energy sources considered, at least in the current technique, refer to: tides, sea currents,

waves, temperature differences of sea water layers. Ocean waves carry massive amounts of

energy but this energy is difficult to exploit efficiently and cheaply.


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Homework 9.3: Identify with the help of internet resources some other technological

solutions for revaluation of the seawave energy potential

9.1.5. SELF-TESTS

1. Which are natural conditions, that do not allow the revaluation of the Black Sea

energy potential:

a) tides;

b) marine currents;

c) ocean-thermal energy conversion;

d) difference in salinity.

2. The operation principle of wave energy capture system based on liquid rise is limited

to:

a) the pressure on a large surface is transmitted through a liquid, through pipes to a

smaller area, thus multiplying the force per unit area, carrying out the actioning of an

electric generator.

b) the water ascent as artificial wave on a slope, which is then taken up by the blades of

a generator.

c) the floating systems whose motion due to waves drives a pump which pushes water

from a turbine which in turn drives a generator.

d) all options are correct.

3. The operation principle of wave energy capture system based on under-pressure pipes

refers to :



electric generator.

b) the water ascent as artificial wave on a slope, which is then taken up by the blades of

a generator.




4. The operation principle of wave energy capture system based on liquid piston refers

to :


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electric generator.

b) the water ascent as artificial wave on a slope, which is then taken up by the blades of a

generator.




9.1.6. ASSESSMENT TEST

1. Explain the mechanism of generation of kinetic and potential energy for high waves.

2..Explain the working principle of the wave-driven piston system.

9.1.7. ANSWERS TO SELF-TESTS

1. A; 2. B; 3. A; 4. C.

9.1.8. BIBLIOGRAPHY

1. Baker, N.J., "Linear Generators for Direct Drive Marine Renewable Energy Converters,"

Ph.D. thesis, School of Engineering, University of Durham (UK), 2003.

2. Barstow, S.F., et al., "WORLDWAVES: High Quality Coastal and Offshore Wave Data

Within Minutes for any Global Site," Proceedings of 22nd International Conference on

Offshore Mechanics and Arctic Engineering OMAE '03," Cancun (Mexico), pp. 23-32, 2003.

3. Bechtel Maria, Erik Netz, OTEC - Ocean Thermal Energy Conversion, Sea Solar Power

Incorporated, 2010.

4. Boccaletti Giulio - The Thermal Structure of the Upper Ocean, Atmospheric and Oceanic

Sciences Program, Princeton University, Princeton, NJ, 2003.

5. Bernhoff, H., Sjöstedt, E., and Leijon, M., " Wave energy resources in sheltered sea areas:

A case study of the Baltic Sea," Proceedings of the 5th European Wave Energy Conference,

Cork (Ireland), 2003.

6. Brooking, P.R.M., "Power conversion in a low speed reciprocating electrical generator,"

Conference Record of the International Conference on Electrical Machines ICEM '2002,

Brugge (Belgium), on CD: 452.pdf.

7. Callaghan, J., "Future Marine Energy Results of the Marine Energy Challenge: Cost

competitiveness and growth of wave and tidal stream energy," Research Report, Carbon


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Trust, London (UK), 2006. URL: http://oreg.ca/docs/Carbon Trust Report/Future

MarineEnergy.pdf.

8. Danielsson, O., Thorburn, K., Eriksson, M., Leijon, M., "Permanent magnet fixation

concepts for linear generator," Proceedings of the 5th European Wave Energy Conference,

Cork (Ireland), pp.117-124, 2003.

9. Giosanu Ştefania, Nicolae Florin - Technologies for valorizing the energy potential of the

sea waves, Workshop-RES 2011, The Future of Renewable Energy Sector, Constantza, 27-28

oct. 2011.

10. Leijon, M, "Multi-Physics Simulation of Wave Energy to Electric Energy Conversion by

Permanent Magnet Linear Generator," IEEE Transactions on Energy Conversion, vol. 20

(March 2005), no. 1, pp. 219-224.

11. Lopatoukhin, L.J. et al., "Estimation of Extreme Wind Wave Heights," Joint Technical

Commission for Oceanography and Marine Meteorology (JCOMM) Technical Report No. 9

(WMO/TD-No. 1041), 2000.

12. Mueller, M.A. et al., "Dynamic Modelling of a Linear Vernier Hybrid Permanent Magnet

Machine Coupled to a Wave Energy Emulator Test Rig," Conference Record of the

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