Overview of Wind Energy Tech

8/9/2019 Overview of Wind Energy Tech

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1. Explain in detail, the concept of the Betz limit and give its value.

The German physicist Albert Betz created the concept of the Betz limit in 11.This la! states that the !ind turbine can only convert the maximum value of 1"#$%,!hich corresponds to &.'(, of the )inetics energy of !ind into mechanical energyin the rotor.

The !ind turbines can extract the energy from !ind !hen the !ind passes throughthe turbine. To extract the energy, the !ind turbines need to *bar+ the !ind comingthrough. o!ever, to have 1--( of efficiency, all the mass of !ind should bebarred by the !ind turbine, but this is impossible because if the efficiency is 1--(,there !ill be no !ind leaving the turbine. The figure 1 illustrates the la! of Betz,

sho!ing the !ind entering and leaving the turbine. (1) (2)

$. hat ratio of do!n/stream to up/stream !ind velocities generates themaximum rotor efficiency0

To have the maximum rotor efficiency,d Cp

dmust be defined and set to zero.

The result for this is eual to

1

3 . 2emembering that

=vd

v=

downwind velocity

upwind velocity, this result means that, in order to have maximum

rotorFigure 1:


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efficiency, the do!nstream velocity needs to be1

3of the total up!ind velocity.

3or example, if the up!ind velocity is 'm#s, the do!n!ind velocity must be 1m#s.

'. 4efine the tip/speed/ratio, !hy this is important, and !hat is the optimumvalue range for large '/blade turbines0

The tip/speed ratio is the ratio of the tip speed of blade to !ind speed. This isimportant because the rotor efficiency also depends on the rotation blades speed.hen the blades are too fast, turbulence in one blade may affect the next blade,and if they are too slo!, too much !ind !ill pass through the blades !ith beingconverted in energy. 5n order to maximize the rotor efficiency, the tip/speed/ratiomust be used.

To define the optimum tip/speed/ratio for maximum po!er, !e have the follo!ing

formula6

power

max=4

n

Optimumtip speed ratio

(3)

Thus, the 7ptimum Tip/8peed/2atio for '/blade turbine !ill be bet!een 9 and &.

9. 4efine the optimum spacing of to!ers for a !ind farm in flat open terrainconstructed !ith !ind turbines of '-m blade diameters.

According to the figure $, the distance bet!een the ro!s must be bet!een & and diameters, and the distance bet!een each !ind turbine must be '/& diameters.Thus, assuming % diameters to the distance bet!een the ro!s and 9 diametersbet!een each !ind turbine, !ith a diameter of '-m, !e have6

$1- meters of distance bet!een the ro!s, and

1$- meters of distance bet!een each !ind turbine.


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Figure 2: Lecture Topic 09 !i"d #ower $%stem &esig"

&. hat are the units of *Wind Power Density?

The ind :o!er 4ensity is given by the euation6 Power Density=1

2 v

3

, !here

the units are given in the 85 units6

in )g#m$,

v in m#s, and finally

:o!er 4ensity in atts per area or #m$.

". hat environmental factors affect air density0

The temperature and the atmospheric pressure ;the altitude< are the biggestfactors that can affect the air density. 5n order to correct the air density according tothe temperature and altitude, !e can use the follo!ing euation6

=1.225KtKa , !here =tis the density ratio correlated !ith the temperature, andthe =ais the pressure ratio correlated !ith the altitude.

%. hat is the approx. cost per )ilo!att/hour for current !ind production0 8ee

the .ppt or AEA !eb siteAccording to American ind Energy Association ;AEA8?9-#@h, !hich means >8?-.-9)h. (4)


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. o! many !ind po!er *classes+ are there0 @easured at a '-m location, ifthe !ind blo!s at 19.&mph, !hat class is this0 5f it blo!s at .$m#s, !hatclass is this0 >se the AEA '-m table values.

According to the Table 1 ind :o!er Classes on the ind :o!er Classifications8ection in the lecture, there are % !ind po!er classes.

3or '-m location and 19.&mph6 Class '

3or '-m location and .$m#s6 Class "

. 4escribe in detail the concept or process of ho! a !ind turbine createselectrical energy.

Basically, the !ind turbine transforms the !ind that passes through the blades as a)inetic energy in a mechanical energy, !hich ma)es the blades rotate. hen theblades rotate, the electrical energy has been generated. To achieve thetransformation from mechanical energy to electrical energy, currently, the inductiongenerator is used in order to generate the energy. e also have the synchronousgenerator, but the induction generator reuires less maintenance.

The inductor generation is based on a magnetic field in an induction machine thatis created inside, and this induces a current and net motion in the conductors of therotor. Then, the magnetic field motion ma)es the current induced in the conductorsto !or) the rotors.

1-.ind turbine blades should change their speed as !ind speed changes.Additionally, for grid/connected !ind turbines, a fixed output electricalfreuency is reuired. Therefore, !e !ould li)e to have a variable rotorspeed but a fixed output freuency ie. generator speed. There are several

!ays to effectively change speeds ;from the rotor speed to the output ACfreuency < in a !ind turbine system list and describe at least three more6

a. Change the number of poles in the generator thusly changing theoutput AC freuency.

b. @ultiple generators6 high and lo! speed.

c. @ultiple gearboxes.

d. Darying the slip of induction generators using external resistors.


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11. 4efine the terms6

a. Cut/in indspeed 5t is the speed !hen the !ind turbine starts to

rotate and generate po!er. 5t is usually bet!een ' and 9m#s. (5)b. 2ated indspeed 5t is the speed !hen the electrical generator is in

its limit of the po!er output. 5t is usually around 1%m#s. (5)

c. Cut/out indspeed 5t is the speed !hen the !ind turbine is in itsmaximum rotation, !hich means a great ris) of damage in the rotor. 5tis usually around $&m#s. (5)

d. Blade :lanform and 8olidity ;indicate !hat value of solidity is good forelectrical production< Blade :lanform is the shape of the fla!iseblade surface, and 8olidity is the ratio of total rotor planform area tototal s!ept area. To electrical production, the 8olidity value must be

-.1- for large plants of !ind generation, and -.- for small plants of!ind generation.

1$.

Fabel the parts $,&,",,,1-,1' above.

$6 @ain shaft&6 ub

"6 Gearbox

6 acelle cover

6 5nduction

1-6 igh/speed shaft


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1'6 Ha!

REFERENCES:

(1)

Limite de Betz. 2etrieved from6 Ihttp6##!!!.aerogeradores.org#limitedebetz.php

(2)

uleihil, @ahmoudJ @azor, Gedalya. Wind Turbine Power: The Betz Limit andBeyond. 2etrieved from6 Ihttp6##cdn.intechopen.com#pdfs/!m#91-%.pdf

(3)

Wind Energy Math al!ulations. 2etrieved from6Ihttp6##!!!.mmpa.org#>ploadedK3iles#$c#$c9c"c/'-'d/9fc%/d/$1&'1-d1fcc.pdf

(4)

ost o" Wind Energy. 2etrieved from6Ihttp6##!!!.a!ea.org#2esources#Content.aspx05temumberL&&9%

(5)
http://www.aerogeradores.org/limitedebetz.phphttp://cdn.intechopen.com/pdfs-wm/41078.pdfhttp://www.mmpa.org/Uploaded_Files/2c/2c48c69c-303d-4fc7-8d88-2153190d1fcc.pdfhttp://www.mmpa.org/Uploaded_Files/2c/2c48c69c-303d-4fc7-8d88-2153190d1fcc.pdfhttp://www.awea.org/Resources/Content.aspx?ItemNumber=5547http://www.aerogeradores.org/limitedebetz.phphttp://cdn.intechopen.com/pdfs-wm/41078.pdfhttp://www.mmpa.org/Uploaded_Files/2c/2c48c69c-303d-4fc7-8d88-2153190d1fcc.pdfhttp://www.mmpa.org/Uploaded_Files/2c/2c48c69c-303d-4fc7-8d88-2153190d1fcc.pdfhttp://www.awea.org/Resources/Content.aspx?ItemNumber=5547


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#$% Wind turbine power ouput &ariation with steady wind speed. 2etrieved from6 Ihttp6##!!!.!ind/po!er/program.com#turbineKcharacteristics.htm

Overview of Wind Energy Tech

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