Wind Power Physics
Summary
TLDRThis presentation delves into the physics of wind power, explaining the differences between Savonius, Darrieus, and horizontal axis turbines. It emphasizes the importance of wind speed and turbine design for efficiency, highlighting that power in the wind is cubically related to speed. The script also stresses the need for proper turbine placement to avoid low and turbulent wind speeds, and warns against installing turbines on buildings due to inefficiency and vibration issues. It concludes with the message that while small turbines have their uses, larger ones are necessary for significant electricity generation.
Takeaways
- 🌪️ There are three main types of wind turbines: Savonius, Darrieus, and Horizontal Axis.
- 📐 Savonius turbines are drag-based and have slow tip speeds, making them less efficient compared to other designs.
- 🏗️ Darrieus turbines are also vertical axis but use airfoil blades, allowing for moderate to fast tip speeds and higher efficiency.
- 🌀 Horizontal axis turbines have fast tip speeds due to their airfoil design, which can lead to higher efficiency.
- ⚙️ The power in the wind is directly related to the cube of the wind speed, making even small increases in wind speed result in large increases in power.
- 💡 Wind turbines are most effective in areas with high wind speeds and minimal turbulence.
- 🏙️ Avoid placing wind turbines in urban areas or on buildings due to low wind speeds and turbulence.
- 📉 The Betz Limit calculates the maximum theoretical efficiency of a wind turbine to be 59.3%.
- 🔁 Faster blade tips result in less wake rotation and higher efficiency.
- 🌐 The size of the turbine is crucial; larger turbines can capture more wind and produce more power.
- 📈 The power curve of a turbine shows its actual performance, including any drops due to overspeed protection or other factors.
Q & A
What are the three main types of wind turbines discussed in the presentation?
-The three main types of wind turbines discussed are Savonius, Darrieus, and Horizontal Axis turbines.
How does the Savonius turbine differ from the Darrieus and Horizontal Axis turbines?
-The Savonius turbine is a drag-based design with slow tip speeds and is generally less efficient. Darrieus and Horizontal Axis turbines use airfoil blades, allowing for higher tip speeds and greater efficiency.
Why is wind speed so crucial in generating power from a wind turbine?
-Wind power is exponentially related to wind speed, meaning small increases in wind speed can lead to significant increases in power output, as power is proportional to the wind speed cubed.
What is the maximum theoretical efficiency a wind turbine can achieve, and who calculated it?
-The maximum theoretical efficiency a wind turbine can achieve is 59.3%, known as the Betz Limit. It was calculated by Albert Betz.
Why do turbines in urban areas tend to produce less power?
-Turbines in urban areas tend to produce less power because urban environments have low wind speeds and high turbulence, which reduce the efficiency and power generation of turbines.
Why should wind turbines not be placed on buildings?
-Wind turbines should not be placed on buildings due to low wind speeds and high turbulence around buildings, which reduce efficiency. Additionally, they can cause vibrations that may disturb the building's occupants.
What is wake rotation, and how does it affect turbine efficiency?
-Wake rotation refers to the energy lost when the air molecules leave the turbine blades spinning. Faster blade tip speeds reduce wake rotation, making the turbine more efficient.
What is the relationship between the size of a wind turbine and the amount of power it generates?
-Larger wind turbines have a larger swept area and can capture more wind energy, generating more power. Smaller turbines generate significantly less power, often only enough for minor uses like charging batteries.
What factors should be considered when choosing a location for a wind turbine?
-Key factors to consider are avoiding areas with low wind speeds and high turbulence. Turbines should be placed in open areas, high above obstacles, to access clearer and faster winds.
What happens to the power output of a turbine if the wind speed exceeds its design limits?
-If the wind speed exceeds the turbine's design limits, the turbine may engage overspeed protection mechanisms, which reduce power output to prevent damage, resulting in a drop in power generation.
Outlines
🌬️ Introduction to Wind Turbines
The video script introduces the physics of wind power, explaining the basics of wind turbines and the factors that affect their efficiency. It discusses three main types of turbines: Savonius, Darrieus, and horizontal axis. The script describes the Savonius turbine as resembling a half-barrel and functioning similarly regardless of its appearance. Darrieus turbines are vertical axis designs with airfoil blades, also varying in appearance but functioning similarly. Horizontal axis turbines have their axis and generator set horizontally and also feature airfoil blades. The physics of wind is then linked to kinetic energy, with the script explaining the formula for calculating the power of wind, which is related to the air's density, the swept area of the turbine, and the cube of the wind speed. The importance of wind speed is highlighted, as power is exponentially related to it.
🔍 Understanding Wind Power Efficiency
This section delves into the efficiency of wind turbines, emphasizing the importance of wind speed and the cubic relationship between power and wind speed. It explains that while turbines may spin at low wind speeds, there is very little power to convert into electricity at these speeds. The script mentions the theoretical maximum efficiency of wind turbines, known as the Betz limit, which is 59.3%. It also discusses the wake rotation and how faster blade tips can reduce wake rotation losses, increasing turbine efficiency. The summary also touches on the characteristics of the three types of turbines, with Savonius turbines having slow tip speeds due to their drag-based design, while Darrieus and horizontal axis turbines have faster tip speeds due to their airfoil design, leading to higher efficiency potential.
🏠 Choosing the Right Turbine Location
The script advises on the proper placement of wind turbines for optimal power generation. It stresses the importance of avoiding slow and turbulent winds, and specifically warns against placing turbines on buildings. The text explains that turbines need to be placed well above any obstacles, such as houses or trees, to ensure they are in higher wind speeds and less turbulent air. It gives specific measurements, suggesting that a turbine should be at least 20 times the height of an obstacle in the downwind direction and at least twice the height in the upwind direction. The section also provides examples of poorly sited turbines and the issues they face, such as being in turbulent areas, low to the ground, or causing vibrations in buildings.
💡 Maximizing Wind Turbine Output
The final paragraph focuses on maximizing the output of wind turbines by choosing the right design and location. It reiterates the importance of high wind speeds and clear, unobstructed locations for the best performance. The script contrasts small turbines, which are limited in the amount of power they can produce, with larger turbines that can generate significant amounts of electricity. It also provides resources for further information, including websites and a YouTube channel, and mentions that the presentation is produced by Nebraska Extension.
Mindmap
Keywords
💡Wind Power
💡Turbine
💡Savonius Turbine
💡Darrieus Turbine
💡Horizontal Axis Turbine
💡Kinetic Energy
💡Mass Flow
💡Betz Limit
💡Tip Speed
💡Wake Rotation
💡Efficiency
Highlights
Three types of wind turbines: Savonius, Darrieus, and horizontal axis.
Savonius turbines resemble a cut barrel and have slow tip speeds.
Darrieus turbines are vertical axis with airfoil blades, varying in appearance but functioning similarly.
Horizontal axis turbines have a horizontal generator and airfoil blades, offering high efficiency.
Wind power is based on the kinetic energy of air particles, calculated using mass flow rate.
The power available from wind is directly proportional to the velocity cubed.
Turbines that spin at low wind speeds do not produce significant power.
The theoretical maximum efficiency of a wind turbine is 59.3%, as calculated by Albert Betz.
Faster blade tips result in less wake rotation loss, increasing turbine efficiency.
Savonius turbines are less efficient due to their slow tip speeds and drag-based design.
Darrieus and horizontal axis turbines have higher efficiency potential due to lift and drag.
The power curve of a turbine shows its actual power production compared to the theoretical maximum.
Small turbines produce minimal power regardless of design.
Turbines need to be placed in areas with high wind speeds to maximize power production.
Urban areas typically have low wind speeds and are not suitable for wind turbine placement.
Turbines should be placed well above obstacles and in clear, non-turbulent wind conditions.
Wind turbines should not be installed on buildings due to vibrations and inefficient energy production.
Proper turbine siting and design are crucial for efficient electricity generation.
The power in the wind is calculated using the formula: power = 1/2 * air density * swept area * velocity cubed.
Small turbines are suitable for trickle charging batteries in remote operations.
Transcripts
this presentation is gonna be on the physics of
wind power we are going to cover a lot of the basics and you're have a much clearer understanding
of what makes a good turbine and a not so good turbine
generally there's three types turbines savonius, darrieus, and horizontal axis
the savonious design on the top
looks basically like a barrel that is cut in half and there's all kinds of different
versions at this design
but they of function about the same it doesn't matter if it looks like a shell or
looks like something else it's a savonious design and it fits within that category as
far as
the way it works Darrieus is a
also vertical axis design but has airfoil blades the Darrieus turbines look all
kinds of different
ways as well but again have they all function
about the same in that sense
here's a small one and a large one again we are going to set the axis
horizontal and the generator in a horizontal fashion
and also have airfoil blades if we are going to look at the physics of wind
we think about physics kinetic energy because all wind is
is small particles each having kinetic energy if we're thinking about kinetic energy of
an object
its to 1/2 times the mass times velocity squared
the mass of a ball is pretty easy to calculate we can calculate that if we threw
a ball
its mass its velocity we've got its kinetic energy
wind is little different lots and lots of small particles
of nitrogen oxygen carbon dioxide and other things
all moving so we can't really calculate each individual molecule
so we will use a mass flow of particles
that mass flow is going to be equal to
the density of the air times the swept area of the area were calculating
in this case the swept area of what ever turbine we are going to use
and the velocity of that air
substitute that mass flow in and come up with our equation of
power is equal to 1/2 times a density times the swept area
times the velocity cubed
the wind speed velocity the Swept area A
and effective air density
of greatest importance if we were to look at this equation is the velocity
because we graphed this equation for small wind turbine
and see the power of the wind
is exponential its cubicly related to the wind speed so as I
increase that wind speed
I get whole lot more power so one of the things we see sometimes advertisements
is this turbine will spin at low wind speeds
at those low wind speeds there is very little power
if there's very little wind and if there's very little power we can convert very
low power into
very little electricity and so the reality is it doesn't matter
that is spins a low wind speeds example of that is
two times two times two is eight
and ten times ten times ten is a thousand, I don't care about those low wind speeds, because they don't have any power
And when I don't have any power
I can't convert them into electrical power
In my turbine
and so I need turbines that spin in moderate wind speeds
Where there is a lot more power
every generation system
is less than 100% efficient we cannot capture
all convert one form of energy into a more useful form of energy without losses
and that's true for wind turbines and so if I have the wind is blowing and
say that that way and has all the power it we start with
100 percent if we put that through a turbine
the absolute best that we can do is 59.3 percent if I can imagine those molecules
moving towards a turbine striking the blades of that turbine causing the
rotational energy
and then going beyond the turbine
and and now there's a slower speed because they've given up
some of their energy the absolute
have maximum efficiency possibles 59.3 percent that was calculated by Albert
Betz
and it
has not been proven wrong yet and that's because it was
pretty good calculation and he basically assumed that if
they could give up as much energy as possible and
be behind the turbine it straight hair it would be 59.3 percent but the reality
is
that they're not what happens is that that turbine is
that molecule of air is
giving some his energy to the turbine and then the turbine
as it spins is pushing that molecule causing
it to spend some and that's wasted energy that
causing it to spin or the wake rotation with experiments
scientists found that the faster at the blades spin
the less wake rotation losses occur
and so on when I say the faster I'm particular talking about the tip that
blade
the faster that tip of that blade the less wake rotation
and thus more efficient, So let's make this more simple the faster the tip
more efficient turbine and that is going to
hold true very well through
I'm a lot experiments that have been done in wind and shows that the designs that
have won out
and are the most popular this is true start a look at our three different
types of turbines
now again these are just three pictures turbines are of all different
shapes and sizes but they generally fit the three categories
in that's savonious turbine I have almost a 100% drag machine
in that drag machine I have slow tip speeds because
drag means the particle is striking
really that turbine can only spin as fast as the wind blows
the other two designs because their airfoil and the fact that they have lift
and drag they have much faster tip speeds
and thus they have much greater potential to have higher efficiency
and so already we're seeing savonious turbines
are less efficient then the other two turbines
so they're already handicapped by that
again lets just re look at that savonious have slow tip speed
Darrieus a moderate to fast ship speeds and horizontal axis turbines have fast
speeds and again horizontal axis
could be any type of turbine of that design small or large here's a
a picture of a large one I know what you're think you're thinking about what about
that old Chicago Style wind mill
that we had back farm those have moderate to slow tip speeds due to high solidity
and high drag you can imagine that turbine being somewhat like a cross
between a savonious and
horizontal axis where because I was lifting water and need a lot of
torque forces
they built it to have high solidity
and thus have high drag and so it works
they work very effectively in lifting water up but if we were to you
I try to have that same turbine generate electricity its moderate to slow tip speed
would just show that probably has less
efficiency then the other turbans if I'm to graph all those
these things together the red in this case is power of the wind that's
absolute maximal what's available to me
in the wind that's at 100 percent The Betz Limit
59 percent thats the best I could ever do to capture
its 59.3 percent and finally I got the power curve a little 1k turbine
that shows
actually what it can do so thats what's reality every turbines gonna have
somewhat of a reality
there power curves are gong to be a little different this one has this drop of about 34 miles
an hour and what that is is that sits
protection measure against high wind speeds as a different terms power curves are going to
look different depending on how they deal with that overspeed protection
this when it drops it doesn't drop of to zero but it does drop off
if the wind was to you increase in a linear fashion
so if we are going to look at this basic equation again to get a little more
detail
in this case if I look at roe it is almost equal one
it's 1.2 at low land sites and about
1.0
at upland sites and so I'm just going to ignore it
its close enough to 1.0 it doesn't affect my equation all that much
A is the swept area and I can calculate that using Pi r squared
and however big my turbine is it is
and the bigger the turbine the more power so if I was to see a turbine that was three feet across
I already know it's not a very big turban its not
going to generate very much electricity
because it's not very big, turbines that big create a lot of power
turbines that are small create small amount of power and so
a turbine that is three foot across example might run a couple light bulbs
but to run a house I might need a turbine that is anywhere from 10 to 16
to 25 feet
in diameter to actually run the house
and then of course to run a bunch houses I need even bigger
and so don't think the small turbines are produce power
it doesn't matter which one of those three designs they are, small
turbines
don't produce very much power
Wind speed if I put it turbine in a place with low wind speed, low power
If I put a turbine in a place with a lot of wind speed, a lot of power
and so any turbine that's in an urban area
is going to have not very much power because it's an area slow wind speed
invariably
urban areas have low wind speeds there's very few examples
that's not true and so most cases you can imagine that part that is because
urban areas cause with a lot of
wind shear and cause a lot of slowdown that wind around
so even if you have a windy city, Chicago the Windy City
still inside the city limits Chicago
really inside any of the areas where there's a lot houses and other
things are so much wind shear at if I want a turbine I have to get up way up
above
all those things and if that's feasible great if it's not
don't put anything low to the ground especially in urban
choosing a location, avoid slow wind remember that power in the wind is cubicly related to wind
speed
avoid the slow winds
avoid turbulent wind and never put I wind turbines on buildings
and that goes back to rules number one and two avoid slow winds and avoid turbulance
in this case I have my obstacle or my house
that it and I need to avoid areas that are twenty times
the height to the house really in the downwind direction but also a little bit
me up wind direction
also two times the height of the house, If I am going to put a turbine and
I have a twenty-foot house
that turbine needs to be above forty foot high
and probably even a little more than that about the house
so I need a forty foot tower maybe fifty and then
I might have some 60 ft trees around the house well now I'm
my turbine has to be 120 foot in the air or
greater so I've got all those issues so avoid slow wind avoid turbulent winds
if you want your turbine to produce power if you don't want your turbine to
produce power
go ahead put it wherever you want but again this is where
good turbine that is gonna produce electricity
needs to be placed in a correct location also the right correct designed to get
you the best
opportunity to create electricity here some examples
here are two wind turbines that are on a building here like Lincoln, NE
and after three years these turbines have
effectively produced no power I repeat
three years operation they've never produced any power
and the reason is multiple fold
let's look at this these are bad they're inefficient sign so remember this is
a Savonious design
is inherently inefficient which already gives it a drawback
it's in a turbulent area its low to the ground
this is an office building
and so they've actually had times where they have tied these turbines down
because the vibrations caused by the fact that they did spin
cause noise in the building and so again another reason not to put them on buildings
is that annoying vibration that is difficult to remedy
anybody that says they can
well maybe maybe not but it's a it's a risk
that you face by putting it on
multiple people had a problem not just one Portland Oregon
again here's a design where design of the turbine
is somewhat more reasonable the height
of the turbines look more reasonable and yet
this is not that good again the turbine design is OK
but you have a turbulent wind you can actually see that these four turbines
are facing in four different directions and that's because the wind is so
turbulent up at that site
that it really hampers their
ability to perform I don't have the data for these
but to I'm I'm convinced that they're not probably doing very well
by my observation of them
heres some turbines I took a picture of at a school in Thunder Bay Ontario
there's three turbines in this picture so lets just touch on a little bit
I'm so this is a turbine thats right on top the building their
it shrouded I don't particularly like charter bus because shrouded turbines
cause for small wind turbines because the shroud takes a lot more material
so we may say that that all we're gonna be able that
catch more that wind because we're going to
funnel it into my turbine or some other thing
shrouds say but what what happens is when you build it and you put all that material and
in you end up with a smaller turbine
because of all that shrouds Plus this is low
very low to to the ground so there is very turbulent wind
their slower winds low to the ground again we put on a building
now get deal with that vibration was like this one this is a a little better
design
in the fact that it is
airfoil bladed and is a
horizontal axis turbine so design is ok, it is clear
up in the winds up high you know I'd love to see that our be
another twenty feet higher but again is probably gonna produce
some electricity and and maybe do reasonably well for what it is
so that's that's better here's a third one hiding over here behind the turbine
again I make all this bad
design is a Darrieus type which is
okay except for a lot of darrieus turbine
tend to be designed to for short hours low to the ground
and because its low to the ground you're in turbulent wind you're in slow wind
and it doesn't matter that your signs okay when you place that turbine in a place with slow wind
that's one challenge with that particular turbine
is tends to put them in low wind speeds low to the ground
here's one I took a picture of
again this is a good design and
the turbine itself is a good design but also it siting its
it's clear its up high in clear winds on a tall tower
its gonna produce quite a bit of power here actually one that
that I installed and you can see I didn't put it on the tallest tower
but I also put it very very clear area so
were on top of the hill and there's no trees around
and so again we put this the small wind turbine up
and we're producing quite a lot of power from that turbine
here's pretty good one again same kinda thing
this is a very old design turbine
60 to 70 year-old turbine potentially but
with some maintenance they've been able to keep this going and it's a
pretty good design clear winds up high
tall tower. So lets review the power in the wind
in Watts is equal to one-half times the density air
times the swept area times the velocity cubed remember put these in SI units to get
get proper results we need high wind speeds
that velocity cubed is very very important
if it's not an area with good wind speeds don't expect much production
so open areas are best up high never put a turbine on a building. Big turbines
again we we would drive down the road we see a little turbine
it's not a purse much power now what's the goal that turbine sometimes there is
a use for small turbines
in battery charge a remote operations were just trickle charging a battery
that small turbine may be fine if it's
if its has access to wind right so I'm not saying the small turbines are
don't have their place but realize a small turbine is not going to generate
very much electricity and if I'm expecting it to generate
quite a bit to help me provide for house or something like that
small turbines just are not going to get it done so big
turbines can produce a lot more power conversely small turbines
produce only a very small amount of power if you have more questions
please feel free to visit I have a bunch of different places you can go
bioenergy.unl.edu is my website, I also have a youtube channel Cropwatchbioenergy
and then the
farm Energy Community of Practice at extension
which is set W W W dot extension .org
this presentation has been put together
by Nebraska Extension
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