wind energy and wind turbine.pdf

8/14/2019 WIND ENERGY AND WIND TURBINE.pdf

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Executive summary

This report is about wind turbines in general and wind energy with particular focus on

African countries.

Wind energy is a renewable energy and is available throughout the year. However,

wind intermittency causes major problems to wind turbines when generating wind

power. In addition, wind turbines have to be installed as high as possible to take ad-

vantage of uniform and continuous moving air, plus, wind farms have to be arranged

and set up far away from the community due to noise pollution, and other environ-

mental impacts. But this figure is changing rapidly with the modern designs of wind

turbines. There two types of wind turbines recognised nowadays; the VAWTs and the

HAWTs, with the latter being most used due to their advantages. Africa has a large

coastline, wherewind power andwave power resources are abundant and underuti-

lized in the north and south.

Also seen on this report is that china is the current leader on wind power production,

accompanying next is European countries, then UK and after USA, African countries

being the last with less than 2% contribution to world wind power production.
http://en.wikipedia.org/wiki/Wind_powerhttp://en.wikipedia.org/wiki/Wave_powerhttp://en.wikipedia.org/wiki/Wave_powerhttp://en.wikipedia.org/wiki/Wind_power


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Table of ContentsExecutive summary............................................................................................................................... i

1. Introduction.................................................................................................................................... 1

2. Winds origin.................................................................................................................................. 2

3. Wind Energy and Turbine Development................................................................................... 2

3.1. Wind power variation with wind velocity and altitude...................................................... 2

3.2. How Industries Use Wind Turbines.................................................................................... 3

3.3. Wind Turbine Types............................................................................................................. 3

3.3.1. Horizontal Axis Wind Turbines (HAWTs) .................................................................. 4

3.3.2. Vertical Axis Wind Turbines or Darrieus Turbines (VAWTs) ..................................... 4

3.4. Advantages and disadvantages of wind energy.............................................................. 5

4. Wind Energy Growth.................................................................................................................... 6

5. Africas wind energy resource compared with other countries.............................................. 6

6. Environmental considerations..................................................................................................... 8

7. Conclusion..................................................................................................................................... 9

References.......................................................................................................................................... 10


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1. Introduction

It will be discussed on this assignment wind energy, wind turbine and all benefits thatit can bring to humanity. It also will include Africa as a possible candidate for wind en-ergy.

Wind power is extremely scalable, as there are systems available from less than 1

watt to several megawatts. This makes it possible to initialize the electrification of a

home or village with initial capital. It also allows for dynamic and incremental scaling

as load demand increases. The component configuration of a wind installation also

provides a level of functional redundancy, improving the reliability of the system. The

failure of a single wind tower in a multi tower configuration does not cause a system

level failure.

Because wind projects produce power where it is used, they provide a safe, reliable

and cost effective solution. As transmission equipment is avoided, these systems are

more secure and less vulnerable to attack. This can be an important feature in re-

gions prone to conflict. Wind systems are simple to set up, easy to repair and dura-

ble. Wind resources are abundant enough to provide all of the electrical energy re-

quirements of rural populations and this can be done in remote and otherwise frag-

mented low density areas that are impractical to address using conventional based

systems.

Before any attempt to start any further explanation, it needs to be understood whatwind energy or wind power is and its origin.


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2. Winds origin

Wind power comes from the conversion of wind kinect energy into useful form of en-ergy such as electrical power by using wind turbines, mechanical power by usingwindmill, water pumping or drainage by using wind pumps, etc.

Wind is caused by huge convection currents in the Earths atmosphere, driven byheat energy from the sun; this means as long as the sun shines, there will be wind.The earths surface has both land and water. When the sun comes up, the air overthe land heats up quicker than that over water. The heated air is lighter and it rises.The cooler air is denser and it falls and replaced the air over the land, in the night thereverse happens. Air over the water is warmer and rises, and is replaced by coolerair from land.

The moving air (wind) has huge amount of kinetic energy, and this can be transferredinto electrical energy using turbines. The wind turns the blades, which spin a shaft,which connects to a generator and makes electricity. The electricity is sent through

transmission and distribution lines to a substation, then on to homes, business andschools. Wind turbines cannot work if there is no wind, or if the wind speed is so highit would damage them.

3. Wind Energy and Turbine Development

Wind power is very consistent from year to year but has significant variation over

shorter time scales. The intermittency of wind seldom creates problems when used to

supply up to 20% of total electricity demand, but as the proportion increases, a need

to upgrade the grid and a lowered ability to supplant conventional production can oc-

cur.

Power management techniques such as having excess capacity storage, geograph-

ically distributed turbines, dispatchable backing sources, storage such as pumped

storage hydroelectricity, exporting and importing power to neighbouring areas or re-

ducing demand when wind production is low, can greatly mitigate these problems. In

addition, the weather forecasting permits the electricity network to be become ready

for the predictable variations in production that occur.

3.1. Wind power variation with wind velocity and altitude

Wind energy is the kinetic energy of air in motion, also called wind. Total wind energy

flowing through an imaginary area during the time is:

=1

2 =

1

2() =

1

23

Where: is the density of air; is the wind speed,is the volume of air passing

through(which is considered perpendicular to the direction of the wind); is

therefore the mass m passing per unit time.

Power is energy per unit time. So the wind power incident on is:


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=

=

1

23

Wind power in an open air stream is thus proportional to the third power of the wind

speed; the available power increase eightfold when the wind speed doubles. Wind

turbines for grid electricity therefore need to be especially efficient at greater wind

speeds. In addition, the wind power will vary with altitude as well since air density

varies with altitude. Wind turbines like windmills, are mounted on a tower to capture

the most energy. At 30 meters or more above ground, they can take advantage of the

faster and less turbulent wind. Turbines catch the winds energy with their propeller-

like blades. Usually, two or three blades are mounted on a shaft to form a rotor. [Ref

1].

A blade acts much like an airplane wing, when the wind blows, a pocket of low-pres-

sure air forms on the downwind side of the blade. The low-pressure air pocket thenpulls the blade toward it, causing the rotor to turn. This is called lift. The force of the

lift is actually much stronger than the winds force against the front side of the blade,

which is called drag. The combination of the lift and drag causes the rotor to spin like

a propeller, and the turning shaft a generator to make electricity.

For more theoretical discussion concerning lift generation and turbine blades, the

reader is advised to consult Ref.5,pp. 366-408 or related textbooks on the topic.

3.2. How Industries Use Wind Turbines

Wind turbines can be used as stand-alone applications, or they can be connected to

a utility power grid or even combined with a photovoltaic (solar cell) system. For util-

ity-scale sources of wind energy, a large number of wind turbines are usually built

close together to form a wind plant. Several electricity provides today use wind plants

to supply power to their customers.

Stand-alone wind turbines are typically used for water pumping or communications.

However, homeowners, formers, and ranchers in windy areas can also use wind tur-

bines as a way to cut their electrical bills.

3.3. Wind Turbine Types

Modern wind turbines fall into two basic groups based upon the aerodynamic princi-

ples:

Horizontal axis: such as the traditional farm windmills used for pumping water

Vertical axis: design such as the eggbeater-style Darrieus model.


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3.3.1. Horizontal Axis Wind Turbines (HAWTs)

They comprises a nacelle mounted

on top of a high tower, containing a

generator and, usually, a gearbox

to which the rotor is attached. In-

creasing numbers of wind turbines

do not have gearboxes but use a di-

rect drive. A powered yaw system is

used to turn the turbine so that it

faces into the wind. Sensors moni-

tor the wind direction and the na-

celle is turned according to some

integrated average wind direction.

The number of rotor blades em-

ployed depends on the purpose ofthe wind turbine. As a rule, three-

bladed rotors are used for the gen-

eration of electricity. Wind turbines

with only two or three blades have a high ratio of blade tip speed to axial flow velocity

(the tip-speed ratio), but only a low starting torque and may even require assistance

at start-up to bring it into the useful power producing range of operation. The crucial

parameter is the diameter of the rotor blades, the longer the blades, the greater is the

sweptarea and the greater the possible power output. The trend has been towards

larger machines as they can produce electricity at a lower price.

3.3.2. Vertical Axis Wind Turbines or Darrieus Turbines (VAWTs)

These turbines uses vertical and often

slightly curved symmetrical aerofoils.

Guy cables or wires are required to

maintain the turbine erect. This type of

turbine has one distinct advantage: it

can operate consistently without re-

gard to wind direction. However, it

does have a number of major disad-vantages:

i. Wind speeds are low close to

the ground so that the lower

part of the rotor is rather less

productive than the upper part;

ii. High fluctuations in torque occur

with every revolution;

iii. Negligible self-start capability1;

1Refer to Ref.5,p. 362.

Fig. 2: VAWT egg -beater type turbine. Source:http://visual.merriam-webster.com/images/energy/wind-energy/wind-turbines-electricity-production/vertical-axis-wind-turbine.jpg

Fig. 1: HAWT. Source: http://ec.europa.eu/research/en-ergy/nn/nn_rt/nn_rt_wind/images/wind_en_1370.gif


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iv. Limited capacity for speed regulation in winds of high speed.

Since the end of the 1980s research and development on VAWTs has virtually

ceased in most countries, apart from Canada and most large modern wind turbines

are horizontal axis turbines due to the disadvantages presented by the VAWTs. [Ref.

5]

3.4. Advantages and Disadvantages of wind energy

The main advantage of wind energy is that harnessing it doesnt disrupt natural pro-

cesses or harm the environment, unlike a lot of other energy sources. To generate

electricity on a large scale, a number of windmills are set up over a large area, called

a wind energy farm.

Advantages

Wind energy is an inexhaustible source of energy and is virtually a limitless

resource.

Energy is generated without polluting environment.

This source of energy has tremendous potential to generate energy on large

scale.

Like solar energy can be used directly as mechanical energy.

Windmill generators dont emitany emissions that can lead to acid rain or

greenhouse effect.

In remote areas, wind turbines can be used as great resource to generate en-

ergy.

In combination with solar energy they can be used to provide reliable as wellas steady supply of electricity.

Land around wind turbines can be used for other uses, e.g. farming.

Disadvantages

Wind energy requires expensive storage during peak production time.

It is unreliable energy source as winds are uncertain and unpredictable.

There is visual and aesthetic impact on region.

Requires large open areas for setting up wind farms.

Noise pollution problem is usually associated with wind mills. Wind energy can be harnessed only in those areas where wind is strong

enough and weather is windy for most parts of the year.

Usually places, where wind power set-up is situated, are away from places

where demand of electricity is there. Transmission from such places increases

cost of electricity.

The average efficiency of wind turbine is very less as compared to fossil fuel

power plants. We might require many wind turbines to produce similar impact.

A threat to wildlife: birds do get killed or injured when they fly into turbines.

Maintenance cost of wind turbines is high as they have mechanical parts thatundergo wear and tear over the time. [Ref2]


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4. Wind Energy Growth

The graph on the right shows the growth of wind energy production from 1989 to 2010. It

also shows the exponential increase of the electricity generation from wind energy over the

years.

The graph below (Fig. 4) show the

growth of the power generated from wind

energy from the top 10 main contributors

in the year of 2012. It also shows a sig-

nificant leap of growth in implementation

of wind turbines and production of wind

energy that have occurred in China

which has become the leading contribu-

tor.

Fig. 4: Top 10 countries by nameplate wind power capacity (2012 year-end)

4.1.Africas Wind Energy Resource Compared with other countries

Africa has a huge wind energy reserve just waiting to be tapped compared with other

developing regions, a study presented before an economic conference concerning

the regions shows. According to a paper presented at the 2012 African Economic

Conference, out of the 27 developing countries across all continents that hold the

highest potential for wind energy, eight are in African region. These are Somalia, Su-

0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000

China

United States

Germany

Spain

IndiaUK

Italy

France

Canada

Portugal

(rest of world)

World total

ChinaUnited

States

Germa

nySpain India UK Italy France

Canad

a

Portug

al

(rest of

world)

World

total

% world total 26.7 21.2 11.1 8.1 6.5 3 2.9 2.7 2.2 1.6 14.1 100%

Wind power total capacity (MW) 75,324 60,007 31,308 22,796 18,421 8,845 8,144 7,564 6,200 4,525 39,853 0

New 2012 capacity (MW) 12,960 13,124 2,145 1,122 2,336 1,897 1,273 757 935 145 6,737 0

% world total Wind power total capacity (MW) New 2012 capacity (MW)

Fig. 3: Electricity production from wind energy all over the world


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dan, Libya, Mauritania, Egypt, Madagascar, Kenya and Chad. For instance, Maurita-

nias wind potential is around four times its annual energy consumption in tons of oil

equivalent, Sudans wind potential, on the other hand, corresponds to 90% of its

yearly energy needs. Other African countries that have good prospects for large off-

shore wind energy resources are Mozambique, Tanzania, Angola, South Africa and

Namibia. [Ref.4]

The Koudia Al Baida Farm in Morocco, is the largest wind farm in the continent.

There are also projects being planned in South Africa to implement the use of a wind

farm, or large, commercial scale operations, the construction of these wind farms is

being planned for west coast, north of Cape Town. Kenya plans on building a wind

farm the Lake Turkana Wind Power (LTWP) in Marsabit County.The first 5090 MW

from (LTWP) are scheduled for 2015. LTWP is planned to produce 300 MW of wind

power at full capacity.

In January 2009, the first wind turbine in West Africa was erected in Batokunku, a vil-

lage in The Gambia. The 150 kW turbine provides electrical power for the 2,000-peo-

ple village.

From the graphs below, much is seen that Egypt is the top leader contributing 1.76%

to world wind energy production followed by Morocco which contributes approxi-

mately 0.93% both since 2010. Next follows Ethiopia with 0.16% (2012), Cape Verde

0.08% (2012), and South Africa with only 0.03% (2012). Madagascar and Namibia

basically are infants what concerns to wind energy production. What is also noticea-

ble is that African countries have been putting their fingerprints in the wind energygeneration as it can be seen from the increase in production of wind farms from the

graphs below.

Fig. 6: This table provides end-of-year installed wind power capacity (in megawatts) for the countries of the world for theyears 2002 through 2012. Data source: Ref. 7.

2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012

World 31180 39295 47693 59024 74123 93930 120903159213196630237022282482

Egypt 69 180 145 145 230 310 390 430 550 550 550

Morocco 53.9 53.9 53.9 64 64 125.2 125.2 253 286 291 291

Ethiopia 30 30 51

Cape Verde 0 0 2.78 2.8 2.8 2.8 2.8 2.8 25.5 38.3 24

South Africa 13 16.4 16.55 16.6 16.6 16.6 21.8 21.8 10 10.1 10.1

Madagascar 1.2 1.2 1.2

Namibia 0 0 0 0 0.3 0.5 0.5 0.5 0.2 0.2 0.2

0100

200

300

400

500

600

WINDP

OWERCAPACITY(MW)

Installed Wind Power Capacity (MW) 2002 -2012


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Fig. 7: Percentage of wind energy production amongst African countries that produce wind energy

5. Environmental considerations

Where wind farms are to be installed for wind energy production is a great matter that

is judiciously discussed. Investigations of acceptability have shown, due to public

complaints, wind farms needed to be installed far away from the community. Nowa-

days, medium- and large-size wind turbines in small numbers (i.e., 20 to 30) are re-

garded as beneficial to the community; first, the graceful, almost hypnotic turning of

the slender blades of the larger turbines, seemingly in slow motion, has generally led

to a more positive aesthetic reaction, in most surveys. Second, the perceived benefit

to the community with part or total ownership, giving lower power costs and possibly

even preferential availability of power. And comes from the amount of careful plan-

ning and cooperation between the installers and the leaders of the community long

before any work on installation commences. It is a strange fact that the old-fash-ioned, disused windmills, now local landmarks that abound in many parts of Europe

are now widely accepted.

Wind turbines undoubtedly generate some noise but, with the improvements in de-

sign in recent years, the level of noise emitted by them has dropped remarkably. A

problem occurs in connection with small wind turbines. These turbines are sold in

large numbers in areas remote from electric utilities and are often installed close to

2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012

Egypt 0.22 0.58 0.47 0.47 0.74 0.99 1.25 1.38 1.76 1.76 1.76

Morocco 0.17 0.17 0.17 0.21 0.21 0.40 0.40 0.81 0.92 0.93 0.93

Ethiopia 0 0 0 0 0 0 0 0 0.10 0.10 0.16

Cape Verde 0 0 0.01 0.01 0.01 0.01 0.01 0.01 0.08 0.12 0.08South Africa 0.04 0.05 0.05 0.05 0.05 0.05 0.07 0.07 0.03 0.03 0.03

Madagascar 0 0 0 0 0 0 0 0 0 0 0

Namibia 0 0 0 0 0 0 0 0 0 0 0

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

%OFINSTALLEDWIN

DPOWER

Installed Wind Power Capacity (%) 2002 -2012

Egypt Morocco Ethiopia Cape Verde South Africa Madagascar Namibia


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peoples homes, often tooclose. There is an urgent need for reliable data on the lev-

els of noise generated so that homeowners and communities can then reliably antici-

pate the noise levels from wind turbines prior to installation.2

6. Conclusion

Wind power, as an alternative to fossil fuels, is plentiful, renewable, widely distrib-

uted, clean, produces no greenhouse gas emissions during operation and uses little

land. The effects on the environment are generally less problematic than those from

other power sources. Wind is far less uniformly distributed than solar resources, with

optimal locations positioned near special topographical funnelling features close to

coastal locations, mountain ranges, and other natural channels in the north and

south. The availability of wind on the western coast of Africa is substantial, exceeding

3,750 kWh, and will accommodate the future prospect for energy demands.

Africas reserves of renewable energy sources are the highest in the world, and the

continent has enough renewable energy potential to meet its future energy needs

[According to the World Energy Council].

Of the top 35 developing countries ranked highest in renewable energy reserves, 18

are said to be found in Africa.

But despite the high wind energy potential in particular African countries, wind pow-

ered electricity generation is still very limited. Notably, wind-based electricity contrib-utes less than 1 percent to installed electricity generation capacity on the continent.

However, it seems that African countries generates much less wind energy (less than

2%) compared to China, European countries, and USA. What stutters the most is

that Africa is very rich in renewable, in particular wind, but it cannot channel this en-

ergy into a useful form.

2An extract of Ref.5,pp. 408-410.


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References

1. http://en.wikipedia.org/wiki/Wind_power2. www.ianswer4u.com/2012/02/wind-energy-advantages-and.html

3. http://en.wikipedia.org/wiki/Renewable_energy_in_Africa

4. http://www.ecoseed.org/business/other-markets/15784-african-region-s-wind-resource-better%20-compared-with-other-countries

5. Dixon, S. L., Hall, C. A.: Fluid Mechanics and Thermodynamics of Tur-

bomachinery, 6thed., 2010. Butterworth-Heinemann, pp. 357-411.

6. Eastop, T. D., McConkey, A.: Applied Thermodynamics for Engineering Tech-

nologists, 5thed., 1993. p. 698

7. http://en.wikipedia.org/wiki/Wind_power_by_country
http://en.wikipedia.org/wiki/Wind_powerhttp://en.wikipedia.org/wiki/Wind_powerhttp://www.ianswer4u.com/2012/02/wind-energy-advantages-and.htmlhttp://en.wikipedia.org/wiki/Renewable_energy_in_Africahttp://www.ecoseed.org/business/other-markets/15784-african-region-s-wind-resource-better%20-compared-with-other-countrieshttp://www.ecoseed.org/business/other-markets/15784-african-region-s-wind-resource-better%20-compared-with-other-countrieshttp://www.ecoseed.org/business/other-markets/15784-african-region-s-wind-resource-better%20-compared-with-other-countrieshttp://www.ecoseed.org/business/other-markets/15784-african-region-s-wind-resource-better%20-compared-with-other-countrieshttp://en.wikipedia.org/wiki/Wind_power_by_countryhttp://en.wikipedia.org/wiki/Wind_power_by_countryhttp://www.ecoseed.org/business/other-markets/15784-african-region-s-wind-resource-better%20-compared-with-other-countrieshttp://www.ecoseed.org/business/other-markets/15784-african-region-s-wind-resource-better%20-compared-with-other-countrieshttp://en.wikipedia.org/wiki/Renewable_energy_in_Africahttp://www.ianswer4u.com/2012/02/wind-energy-advantages-and.htmlhttp://en.wikipedia.org/wiki/Wind_power

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