Wind Power Physics

Summary

This 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

00:00

🌬️ 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.

05:00

🔍 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.

10:03

🏠 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.

15:06

💡 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.

Keywords

💡Wind Power

Wind power refers to the process of converting the kinetic energy from wind into electrical power using wind turbines. The video script discusses the physics behind wind power, explaining how different turbine designs interact with wind to generate electricity. Wind power is a renewable energy source and a key theme of the video.

💡Turbine

A turbine is a mechanical device that extracts energy from a fluid flow, such as wind, to produce rotary motion. The script covers different types of wind turbines, including Savonius, Darrieus, and horizontal axis turbines. Each type has unique characteristics that affect their efficiency and suitability for different wind conditions.

💡Savonius Turbine

The Savonius turbine is a type of drag turbine that looks like a barrel cut in half. It operates on the principle of drag, causing the turbine to spin as wind pushes against its curved surfaces. The script mentions that despite various designs, all Savonius turbines function similarly and are characterized by slow tip speeds.

💡Darrieus Turbine

The Darrieus turbine is a vertical-axis wind turbine with airfoil blades that operate on the principle of lift. The script explains that these turbines can have various appearances but function similarly, offering moderate to fast tip speeds and potentially higher efficiency compared to Savonius turbines.

💡Horizontal Axis Turbine

Horizontal axis turbines (HATs) have their rotors parallel to the ground, similar to a traditional windmill. The script mentions that these turbines also use airfoil blades and can achieve fast tip speeds, which contributes to their efficiency in converting wind energy into electricity.

💡Kinetic Energy

Kinetic energy is the energy possessed by an object due to its motion. The script discusses how wind is composed of numerous particles, each with kinetic energy. The power available from the wind is calculated using the formula involving the mass flow of air particles, their velocity, and the swept area of the turbine.

💡Mass Flow

Mass flow in the context of wind power is the amount of air passing through a given area per unit time. The script uses the term to describe how the kinetic energy of wind is calculated by considering the density of the air, the swept area of the turbine, and the wind velocity.

💡Betz Limit

The Betz Limit, also known as the power coefficient limit, is the maximum theoretical efficiency at which a wind turbine can convert wind energy into mechanical energy, which is 59.3%. The script explains that no real-world turbine can exceed this limit due to various energy losses.

💡Tip Speed

Tip speed refers to the speed at which the tips of a turbine's blades move. The script emphasizes the importance of fast tip speeds for achieving higher turbine efficiency. It contrasts slow tip speeds of Savonius turbines with the faster speeds of Darrieus and horizontal axis turbines.

💡Wake Rotation

Wake rotation is the turbulent air flow that forms behind a wind turbine, causing energy loss. The script mentions that faster spinning turbine blades reduce wake rotation losses, thus improving efficiency.

💡Efficiency

Efficiency in the context of wind turbines refers to the percentage of wind energy that is successfully converted into electrical power. The script discusses various factors affecting turbine efficiency, including design, tip speed, and the Betz Limit.

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