How Windmills Work

We've edited a previously posted video to make it a bit more interesting! Why airplanes can fly. Explanation of the Bernoulli’s Principle relating the speed of the wind and the pressure. An example using fans is shown. How this relates to windmills, and why they turn. How power of a windmill relates to the radius of the blade and the speed of the wind. How wind speed varies with height. What is inside the part at the top of a windmill. Difference between low-speed / high torque windmills and the ones which make electricity. How offshore windmills are constructed.

[@SkinnyCow.]

Dude's interesting. Learned more watching his videos than ever in school science!

[@swillm3ister]

@Wroger Wroger LoL Physics professor = 0 Random youtube commenter = 1

[@waynebreivogel1742]

@Wroger Wroger Nope, it will happen if the airflow is at an angle. I entertain my grandkids all the time with it. I use a leaf blower, at up to about 45°, and sit a ball in the air stream. I use balls of different sizes and weights, they all float.

[@IhateYoutube]

@Wroger Wroger And that is why you're not a Nuclear Physics Professor. :)

[@codydebo1876]

As someone who works in the wind industry it is considered a bit taboo to refer to them as “windmills” as they don’t “mill” anything. The generally accepted nomenclature is “wind turbine generator” abbreviated WTG. Or as you said once in the video, “wind turbine”. Fantastic video and I hope to see more videos on wind as it continues to grow. People want to know more.

[@codydebo1876]

However, as a counter to my point, many people still refer to them as windmills and if they are looking for info online about them, they will likely search for how “windmills” work. So perhaps the title is appropriate if mention of the nomenclature is mentioned in the video.

[@vidznstuff1]

Wind Turbine Driven Alternator, actually.

[@andrewberridge4630]

I live in a windmill. So yes, it slightly frustrates me to hear these things called windmills

[@ccmps]

I can't stress how important is the fact that the economics of energy production, are a subject on these videos. It is absolutely important that anyone designing a new way to produce energy, take the economic aspect of it into consideration, otherwise, we end up with a collection of beautiful (and impractical) ideas. Congratulations on another great video!

[@anthonycalia1317]

You have the unique ability to describe things in a manner that all can understand

[@my_namejeff9770]

i wasnt in the mood of watching entire 19 min video, but video was so packed with information, couldnt even skip 10 seconds. great work. subscribed.

[@Sgrunterundt]

I expected better of this channel than the old Bernoulli misconception about how airfoils work.

[@oobermate]

Give it a chance. This is corrected later on in the video and the content of this channel is amazing

[@ThatProduceGuy_]

Amazing new content. I know KZbin isn’t your job but working with some other KZbinrs like Real Engineering, Wedover Productions, Cold Fusion, PBS Spacetime or RealLifeLore to bring out specialized videos about engineering/physics, entrepreneurship, Economics, or policy would be top notch. Personally I’m studying economics I’m university so seeing content about how to start business’s in the energy industry would personally be very valuable. Love the content can’t wait for more.

[@aellis6692]

Plz do a video with real engineering or wendover productions

[@oobermate]

A collaboration video/videos would be incredible!

[@wr44]

How does someone dislike this video? It's called "How Windmills work" - surely anyone not interested enough to watch it would never have clicked. And everyone that did, learnt something.

[@vidznstuff1]

Because he's pushing academic Bernoulli nonsense instead of Newtonian lift used by aerospace and people who realize there's a reason why hang gliders, birds, your hand out the car window, and insects can fly or have lift.

[@thedillestpickle]

@@vidznstuff1 It's not nonsense. It's just not the entire story. And he does talk about the other part. I assume it's because he uses a squeaky marker

[@ronjon7942]

@@thedillestpickle vid's not wrong.

[@Dappa2097]

Yess, amazing. Keep the new content up regularly and you'll be at 100k subs within a year.

[@jonathanmartins7744]

agreed!

[@sarcasmo57]

@@jonathanmartins7744 His subs have doubled already this week.

[@haewien]

@@sarcasmo57 people are too dumb...

[@authentic6825]

I never had a teacher more genuinely passionate about their profession. Good stuff

[@rzmonk76]

To Dr Ruzic, University of Illinois, and Producers, Happy thanks giving and thanks for making it available to the public.

[@misium]

3:35 The air doesn't need to stay together at the end of the wing. You dont need to create a pocket of vacuum if it doesn't stay together. In fact, experiments have shown it does not stay together. This explanation is not only insufficient, its wrong.

[@ziggystardust4627]

I think he acknowledges this in his subsequent comments. He says that it's much more complex than he described here. The best explanation I've seen on lift: www.av8n.com/how/htm/airfoils.html

[@spaceghost8995]

@Wroger Wroger I would bet this guy is WAY smarter than you.

[@ralanham76]

@Wroger Wroger I think you're right about the motor blocking air but you can do the same thing with a screwdriver and a air gun and that has no hole of air

[@tommypetraglia4688]

@Wroger Wroger Should've known... a red pilled incel.

[@viarnay]

the air stay together on a laminar flow

[@AnishChari]

I love windmills. They keep us cool.

[@SpecialEDy]

Wings and propeller blades don't work because of the Bernoulli Principle. They work because of Newton's Third law. The shape of an airfoil or a surface with a positive angle of attack, forces air downwards. The air is the reaction mass, the airfoil forces the airflow downwards and there is an equal and opposite force of lift on the wing in the opposite direction.

[@majoorF]

each and every time I watch one of your video's I learn something new!

[@randyhavener1851]

Thanks David! More great content!!! It would be fascinating to see how the pitch of the blades is governed.

[@richardhenry5858]

Why is this educator/speaker giving away these university lessons for free on KZbin? Don't get me wrong, I'm sure appreciative of such lessons, but it seems like people pay absorbent amounts of money to learn this stuff. He's an exceptional professor.

[@oobermate]

The generated pressure differential between the air flowing over the wing versus the comparatively higher pressure of the air flowing under the wing generates lift. Man, I absolutely adore these videos. Especially the videos pertaining to nuclear energy and nuclear physics.

[@solarbrianyvonne]

Good Video! We have a Wind Turbine on our off grid farm , your explanation helps us understand how it works. Subscribed !

[@ronjon7942]

Oh, and by the way, love your channel! I've subscribed, of course, and have been unable to take a break from viewing your lessons. When I was researching the Chernobyl accident, your relevant essays were recommended, I got hooked, and have been bingeing on them for a few days now.

[@santasanta-df8td]

thank you for making these video, they make learning fun.

[@florianlucs7229]

we have mastered nuclear fission, spaceflight and invented sliced bread, but the pen keeps on squeaking.

[@hardcard254]

As it should.

[@joaquinel]

Oh... I just commented almost the same. I think it is on purpose, to keep the class awake. Not that this particular guy needs it.

[@yamilabugattas3895]

These videos are great, I like how they are structured. It really engages the viewer in the very interesting topics of energy generation.

[@2014andBeyonD]

I can listen to this guy all day long.

[@antoniomaglione4101]

I recently discovered your channel and I found the teaching to be exceptionally good. It is Google don't push educational video very much, possibly because the majority of them is either outdated or too personality-oriented. This is pure engineering properly taught. I wrote this just to communicate my appreciations to "Energy Professor" and the University of Urbana. Thanks...

[@4Leka]

I find this explanation of how lift is generated more confusing than helpful, as it is backwards. The wing creates a low-pressure area above it, which makes the air move faster into the low-pressure area. The speed of the air is the consequence of low pressure, not its cause!

[@kodymagill4048]

Thank you for all your content! I’m bored with my time and now I’m obsessed with your classes 😊

[@yiming8290]

I love everything about this channel except for his squeaky marker

[@Ryan-lk4pu]

I have no idea why but I actually like the squeaking 🤣

[@rossadew4033]

Damn you and your comment!! Now Squeaking is all I hear!

[@majoorF]

You can also say that the squeaky marker pulls in the viewers. It makes it more personal. If it where to be a asmr squeaky marker that sounds like it's moving from ear to ear when wearing headphones. how would you feel then?

[@scotthix2926]

You should become a mechanical engineer. This is what we do

[@hosmerhomeboy]

i got offered a job doing rebar for windmill foundations once. At first the scale of it struck me as crazy, but after thinking of the leverage on a giant stick coming out of the ground against high winds, it made sense.

[@ralanham76]

I was very happy when you got to the part about the torque on the top of the windmill

[@scheimong]

Ah that's a cool trick. Writing on a piece of glass facing the camera and then flipping the video. For one second before I figured out what was happening I was shouting 'how do you do that!?"

[@arturoeugster7228]

Sir you are a superb teacher, but with all due respect the airfoil aerodynamics are in correct: The lift is produced by the circulation, which depends on the AOA, a result of the starting vortex to separate from the upper trailing edge, the clock wise circulation is equal but opposite to this starting vortex Lift = dens. × Vel.× span × circ. Continuity plus circulation determined by the boundary conditions determines flow geometry, and pressure is determined, as you say , by Bernoulli's energy conservation The smooth trailing edge flow, equal local speed top and bottom trailing edge, the Kutta condition, determines the circulation, by continuously shedding a vortex if necessary. Please the flow separating at the leading edge never arrive at the same time on the trailing edge. That effect is an order of magnitude too weak. circulation is the integral of the scalar product of the local velocity and the path element around any path encircling the airfoil. (m²/s)

[@arturoeugster7228]

Power = dens × (2/3 wind)³ × Area This is the Betz maximum when the wake equals ⅓ wind then the windspeed through the rotor disc is 2/3 windspeed way ahead. The power is usually lower when the wake speed is higher, as controlled by the blade controllable incidence angle.

[@ronjon7942]

@@arturoeugster7228 This is great! Thanks Arturo! Obviously you're an aerodynamicist, or studying to be one...what's your story??

[@arturoeugster7228]

@@ronjon7942 You are familiar wiith Prandtl, who directed aerodynamics at Götingen. one of his students was Ackeret, who formulated the theory of supersonic lift, He taught at the swiss federal institute of technology and I was lucky too be able to graduate under him in aerodynamics and gasdynamics, the thermodynamics of fluid flow, that describe all the equations needed to analyse turbo machinery . The one important point I learned from you is that using integrated coal gasification, makes the removal of nitrous oxides and sulfur dioxide much easier, allowing to power gasturbines using syngas, or by using the Sabatier reaction after the watershift reaction, where hydrogen is obtained and the also produced co2 to produce methane for general distribution as NG, with some hydrogen added, which seems useful in certain applications. The enourmous advantage of the combined cycle is the high efficiency exceeding 62% with the GE aeroderivative gasturbines, with future improvements when the new GE90X engine is industrialized, meaning same cycle, and crucial materials like CMC, with reduced cost due to the removal of the weight constraints and the need to operate at high altitudes. CMC : ceramic matrix composites. As you can imagine, when you have a reliable way for co2 capture you can recirculate at least part of the CO2 . Thanks for your response.

[@forestpepper3621]

Here is an intuitive way to think about Bernoulli's principle. Imagine a hockey-puck shaped, cylindrical chunk of air moving to the right in a pipe with a diameter of 1-foot. Suppose it takes 1-second for the puck to move past a point along the pipe. Next, suppose you want to move the same volume of air (contained in that puck) passed a point along a narrower pipe with a diameter of 0.5-feet, so that the same amount of air passes in 1-second, the same amount of time. Because the cylinder of air has been squeezed into a smaller diameter pipe, that cylinder of air must become much longer to hold the same amount of air. So to get the same amount of air passed a point in a narrower pipe, in the same amount of time, that air must be moving much faster. Now, if the narrower pipe were inside the wider pipe, and you suddenly eliminate the narrower pipe, the fast moving air from the narrower pipe now has much more volume available, and so we see that the faster moving air, transporting the same amount of air-per-second, has a lower density in the larger pipe, and so exerts a lower pressure.

[@tomr6955]

100kw for that big wind turbine? Can't say I'm "blown away" by that

[@zapfanzapfan]

It's tiny compared to what gets built off shore today. That one was 21 meters in diameter, the latest ones are getting close to 200 meters in diameter. And since power is proportional to radius squared, their power is close to 10 MW.

[@zapfanzapfan]

No, never tried that. I guess it goes on the bucket list :-)

[@tomr6955]

@@LegendLength I do actually, in any substantial wind (enough to get a wind turbine going). The same is driving your car with the window open, you are pushing through heavy air and have to overcome friction, takes a lot of force

[@1MinuteFlipDoc]

and they generally kill a fair number of birds. :(

[@rickoshay6554]

Several years ago, Scientific American published an article about the "shower curtain" issue you brought up as an illustration of the Bernoulli principle. You may want to read it: They came to a very different conclusion.

[@BradleyLayton]

So much better than similar videos I posted while on the faculty at the University of Montana

[@k.chriscaldwell4141]

Bernoulli has little to do with lift inducing airfoils. It's Newtonian. An airfoil pulls down the air above it, like an inverted scoop, and accelerates it downwards behind it. Opposite and equal reaction: Air pushed down, plane pulled up. The air is pulled down and accelerated by the extreme vacuum created on the backside of the airfoil. i.e. it is not due to the very weak electric charge based Coanda effect. There is no way or reason for air above an airfoil to communicate with the air blow it. Bernoulli pressure differentials are derived from the conservation of energy/momentum. A single flowing fluid (liquid or gas) will accelerate if its flow becomes constricted, and, to conserve energy, exhibit a lower pressure. And vice versa. A divided airflow is two air flows, not one somehow in communication with the other--Quantum entangled air flows?! Because the Bernoulli formulas provide a close enough approximation to what is observed, they are used in textbooks and in designing aircraft and airfoils, but Bernoulli is not what is happening. Airfoil shapes can run from the low-speed ones shown here, and found on commercial aircraft and windmills, to the "barn door" shapes found on fighter jets. Low-speed airfoils slightly bunch up/gather the air above and below their front, allowing them to scoop and accelerate downward even more air. They are much more efficient than the "barn door" shape. The airfoils of a Windmill's blades work similarly to that found on commercial jets: Wind flow is guided around a blade's airfoil shape by the vacuum on the surface of the backside of the blade. The change in direction induces an opposite reaction on the blade--the blade moves. As a blade moves, up to a point, the blade's airfoil becomes more efficient because of the bunching/gathering at its front. However, the use of airfoils on the blades of windmills is inefficient. Airfoil shaped blades fail to capture approximately 50% of the possible energy from the wind. The designers of windmills must move beyond the airfoil. Extra: Gravity, not the an aircraft's engines, is the main source of the energy that creates lift and sustains a plane in flight--two-third to three-quarters, or more, of the energy. The engines make up the rest and provide the energy needed to climb. This is substantiated by the fact that planes have non-powered glide ratios (helicopters, auto-rotation). For instance, a 747's glide ratio is 17:1: It can fly unpowered 17 units (miles, feet, meters, km, etc.) for every unit it falls. 17,000 feet travel for every 1,000 feet in descent.

[@ThreeSixFour]

K. Chris Caldwell angle of attack is the most important factor generating lift, likewise when you put your hand out the car window. Relative to the angle attack of the leading edge of your hand. The more aggressive the angle the more force you feel. A neutral angle “feather” will have not much force applied.

[@k.chriscaldwell4141]

​@@ThreeSixFour Not correct. the shape of the airfoil is the most important factor: Camber and chord. Many civilian aircraft airfoils can maintain some degree of lift with a negative angle of attack. Differing airfoil shapes require differing angles of attack to maintain a desired amount of lift. i.e. angle of attack follows airfoil shape. But then, the focus of my comment was not about angle of attack, but instead about airfoil lift generation being Newtonian not Bernoullian.

[@nubi78]

I agree with your explanation. I was told that Bernoulli’s principle falls apart when you have an airfoil that has the same shape above and below. And the fact that the air above and below does not have to arrive at the trailing edge at the exact same time. Nice job!

[@thekalikal]

Sorry but you are wrong. Please see my post above response to vidznstuff1. Regarding gravity being the main source of energy for lift. Sorry but this is completely wrong. It always takes energy to climb "UP" and out of a gravity well. The higher you are in a gravity well the more potential energy you have. That energy that you expend climbing out of the gravity well can then be extracted back as kinetic energy as you move down the gravity well to a lower energy state. This is the principle behind gravity energy storage batteries. Be it pumped storage in the form of water being pumped to higher elevation and extracted back via turbines or moving giant concrete blocks up and down through motors. Gravity itself can never be an energy source as this would be a conservation of energy violation and it would allow for the creation of an over unity machine based on gravity, which we know cannot be done. Why do you think rockets require so much energy to climb out of a gravity well? Why does the available payload mass on a rocket decrease rapidly as you move to higher and higher orbits? Think about the size of a Saturn V which is what was needed to take a tiny capsule and Lunar lander module to the moon. A common misconception is that buoyant forces are an example of gravity giving energy to something as it seems like you are able to climb out of a gravity well to a higher energy potential "for free." And there have been MANY machines designed and built in attempt to use buoyancy as a form of gravitational powered overunity machine. But in reality you are still simply getting back energy that was expended at some earlier point and stored as potential energy. I have to expend energy to push a beach ball down to the bottom of the pool. Or I have to expend energy compressing a can of air so that I can then use it to inflate the ball at the bottom of the pool so that it can lift it up out of the gravity well. When an airplane is climbing it is 100% indeed using its engines to "lift" up and out of the gravity well. And if there was some way to calculate all the losses in the system you could balance out the energy equation down to the chemical energy stored within the fuel. Of course there is also some lift (energy) generated from thermals or ridge lift or even dynamic soaring (which is all manifestations of solar energy or geothermal energy) and a tiny amount from buoyancy which, as from above, was potential energy stored some time in the past. However, NONE OF IT is from gravity because gravity is not an energy source and never can be just as magnetism is not an energy source either. Your example of airplanes gliding is nothing more than converting the gravitational potential energy you gained (be it with actual engines or thermals) and converting it into kinetic energy. Gliders have high lift to drag designs so they can convert much of that potential energy from being higher up in the gravity well into forward motion. However if the glider was crushed into a tight ball by a giant press and then dropped straight down it would still express an identical amount of energy as it hurled towards the ground at hundreds of miles per hour. You don't have any more potential energy riding a bicycle slowly down a gentle grade then you do dropping straight down off a cliff from the same height.

[@neildahlgaard-sigsworth3819]

K. Chris Caldwell the shape and angle of attack are equally important. Remember the angle of attack is measured against the chord line, which is independent of the camber. This means that lift can still be generated at negative angles of attack for aerofoil sections with large amounts of camber.

[@markiangooley]

I grew up in Decatur and went to grad school at UIUC. Returned to Decatur a few times a couple years ago and to the north it’s all windmills now on every slight ridge. Never struck me as that windy... Hey, at least they’ve still got the Clinton nuke plant when the wind isn’t blowing. Of course, arguably the windmills aren’t really necessary...

[@whtbobwntsbobget]

As long as they keep turtles cool I support them

[@PistonAvatarGuy]

WINDMILLS DO NOT WORK THAT WAY!!! GOODNIGHT!

[@icey35]

@@PistonAvatarGuy I scrolled through this comment section looking for precisely this reference.

[@PistonAvatarGuy]

@@icey35 Same. I was surprised that it wasn't at the top of the comments section, people seem to always upvote the joke comments.

[@russellmarkman8952]

Airplanes do NOT fly due to Bernoulli's principle. Nearly all lift comes from angle of attack (yes, plus a small amount from Bernoulli for most planes). For example, aerobatic planes do not have airfoils shaped as shown by the good professor, the wings are symmetrical. Such planes fly perfectly well right side up or upside down. A better way to describe lift is to use Newton, not Bernoulli. The wing takes air from above the airplane and forces it down. 'The equal and opposite reaction' is lift.

[@theflyingmylle]

Did you watch the whole video?

[@strohtaler4698]

also (only) by Bernoulli, a plane would not be able to fly upside down. Neither would most hang gliders fly (nor simple paper airplanes.) (not to speak that the air, assuming no wind, is stationary, that is, speed is zero)

[@theflyingmylle]

strohtaler again, did you watch the whole video?

[@olafv.2741]

The symmetrical wing on an aerobatics airplane produces zero lift if the airflow is perpendicular to the chord of the wing. To create lift you need an angle of attack (AOT) Simplified: nose up when flying normal and nose up (wrt the horizon that is) when inverted.

[@russellmarkman8952]

@@theflyingmylle yes, and your point?

[@AlwaysStaringSkyward]

Great video. That’s a baby wind turbine. A Danish manufacturer is testing huge 2MW turbine systems for sale soon...

[@vidznstuff1]

2MW is boringly standard and has been for a few years. 5MW gets you the chicks these days.

[@AlwaysStaringSkyward]

@@vidznstuff1 that was a typo. Should have been 20MW :-)

[@vidznstuff1]

@@AlwaysStaringSkyward Much better, lol

[@sleepib]

I think your shower curtain hypothesis is incomplete. The shower water is hot, and heats the air pretty quickly, making it more buoyant. When the air in the shower rises, the air on the other side of the shower curtain is pushed in to replace it.

[@77gravity]

I agree, although a cold shower will still produce some curtain movement.

[@shreder89]

great video as always! it would be cool if you could make a video analizing the economic aspect of windmill tecnology and also the operational aspect, i.e: how they integrate the electricty produced to the grid since you cannot control the production as you can with traditional power plants.

[@P98D]

I really enjoy this channel and I think it's quite educational, but I'm sorry to say that that's NOT how a wing works. While Bernoulli's principle basically applies to everything an aerospace engineer does, you really need to be careful with your hypothesis: the air on top of the wing actually moves quite faster than you predicted and using Bernoulli's principle is not "just a simplification" it really is a wrong explanation of the phenomenon. What confuses me is that while calculating the resulting forces is quite a bit more difficult, I will give you that, explaining how a wing works isn't much harder than explaining Bernoulli's principle: it's a matter of Newton's third law, action-reaction, air being pulled down means wing being pulled up to make it simple... Still, I understand that's not the objective of the video, but it would be nice to see the correct explanation more often on educational channels.

[@axelBr1]

Lift being caused by the air going faster over the top was certainly the standard explanation when I was growing up 70s, early 80s. Fairly recently I came across someone pointing out the fact that planes fly perfectly well upside down.

[@maxheadrom3088]

If you like kitesurfing and windmills, come visit the state of Ceará, in Brazil - lots of wind, great food and beautiful nature!

[@guigatavares1]

very good every explanation

[@jonne7725]

Would it be possible to get a presentation about the Sabatier process or is it outside of the curriculum?

[@masterofnegotiation2815]

For anyone curious, the windmill blade cross section is explained here: www.windpowermonthly.com/article/1137943/service-maintain-wind-turbine-blade

[@filone1970]

Dear sir, there's not only 1 type of windmills. There are solutions less problematic to torque, creating noise, or low air speeds. These are becoming an alternative for usage at homes or RVs, where optimization and a fast ROI isn't an issue.

[@riblets1968]

Since the blades' hub is only supported on once side, it also applies an axial torsion on the tower, although I don't know how significant that force is.

[@HillCountryDemo]

Great video. Thanks for sharing your knowledge!

[@markgigiel2722]

Excellent video. I new Bernoulli, I was a FAN of his. I hung out with him and Archimedes at the local pub. We threw darts and floated things in our beer and watched a ball player throw a curve ball. He should cover the curve ball in another video. Hint, it's the laces that matter (but not how you think). A smooth round ball is very difficult, if not impossible, to make curve.

[@vidznstuff1]

You should go bet a case of beer with a good table tennis player on that BS theory.

[@tarjei99]

You can move the heavy stuff to the bottom if you use the windmill to generate pressure in a hydraulic or pneumatic tube. You can share this between several windmills.

[@maxheadrom3088]

Norway's Statoil is building windmills in the Northern Atlantic using their know how on sea oil rigs. Lots of wind up there!

[@LifesVoyager]

I think you're talking about wind turbines. Wind mills were mostly for grinding grain or gunpowder.

[@AlJay0032]

I'm missing the part about windmills destabilizing the power grid because of this power of three relation to the speed of wind and the costs of the storage needed to even out the unsteadiness of wind and the cost of the backup power plants needed in many places because you will have no wind for weeks or months in most locations.

[@docvolt5214]

What are those engineering problems in details? How did they get solved? What's still left to improve? Thank you professor.

[@codydebo1876]

The problem of nonuniform wind force across the swept area of the blades was solved by making micro pitches to each individual blade as it moved through the swept area. Torque on the main shaft is closely monitored to prevent premature wear on the main bearing and gearbox. Great question volt! I hope that answers your question a bit. Also each turbine manufacturer likely has patents on this tech and may have found other solutions.

[@docvolt5214]

@@codydebo1876 so each individual blade changes pitch according to its position during each revolution? That's genius tbh. Thank you for taking your time to answer

[@klausgartenstiel4586]

"windmills *do* work this way! goodnight!"

[@johnparsons9620]

A nice little video about Wind Turbines which I wish I had when I was studying OU T313 a few years ago. From the UK perspective its worth getting hold of Boyle, G. A. (2012) Renewable energy: Power for a sustainable Future (3rd edn), Oxford, Oxford University Press/Milton Keynes, The Open University.

[@remidanvin4057]

Really good as usual 👌

[@pepe6666]

this just ..blew my mind. :D

[@maxheadrom3088]

Hello, Illinois EngeryProf. On your demonstration of the Bernoulli principle with the balloon, I thought of convergence in dynamic control systems. I do this trick with a small styrofoam ball where I make it float near my nose ... the thing is that often the ball will fly away. While the ball is in a certain region the Bernoulli effect will keep is stable but if it move away it enters a divergent regions. I often thing of Climate Change together with these concepts from Dynamic Control Theory. Do these concept apply to climate change? If so, could you do a video about it? Here's how I think (I don't know if this is correct): there are some macro feedbacks in the climate and they seem to have a control element. For instance: ocean's temperature rises -> carbon is released -> plants grow faster -> carbon decreases -> oceans cool. Another one: air temperature raises -> air gets drier -> we have forest fires -> forest allows for new plants and the spread of vegetation bellow the canopies -> carbon is reduced -> air cools down. These loops seem to have been, for a long time, in the convergence region but we are seeing things that, IMHO, seem to be leading the system into a divergence region. Trees will saturate - stop responding to increase of carbon - at some level and if that level is reached they won't be able to control the process. Wildfires are also getting so big and destructive that one year isn't enough to recover the forests and, therefore, next year's dry season will be even drier. This is just "an educated inference of the qualitative aspects" - an euphemism for "a guess" - and that's why I would love if you could do a video about it - if my educated guess is correct, of course. Thanks and please say hello to Dr. Floyd and HAL9000 for me! PS: Please forgive my jokes ... I get in a good mood when I'm learning nice things!

[@jeepxj]

Wish all my profs were this guy

[@hamentaschen]

How do write so well backwards? Anyway. thank you. I wish my college professors were as good at explaining things as you are.

[@ashnur]

hackaday.com/2015/08/28/make-your-own-transparent-whiteboard/

[@hennieodendaal5087]

and left handed too !

[@sunroad7228]

I yet to find one single post on Windmills that discusses Lubrication. You car will hardly keep working if engine's lubricant not changed to the manual, and that is every 10000 km, give and take. That's all when the car is never making more than 100KWh, travelling 100 KM / hour, likely less. How about a device, such as a Windmill, that's advertised as being capable of generating MegaWatts of power per hour? What about Lubrication? And if the Industry managed to create a class of lubricants capable of MegaWatts per hour stresses for 25 years, unchanged, why the same class of lubricants are not used in passenger cars? "Energy, like time, flows from past to future".

[@riblets1968]

That's a good question. While the relatively simple gearing doesn't put nearly the same sort of heat and stress on the lubricant as as gasoline or diesel engine; given their large contact areas, longevity is certainly a factor.

[@andyfeimsternfei8408]

To place things in perspective, how about illustrating how many windmills with batteries, solar with batteries, nuclear with peakers, coal with peakers, etc. it would take for each to supply 100% of the US power? Add in comparisions of construction, fuel, maintenance costs and carbon footprint. It is difficult for people to comprehend how much energy we use. "That's what you need to know!"

[@hummesse]

Cute wind turbines in this video. 100kW ppff. Try 15 MW and 236m rotor diameter, which is the new Vestas turbine.

[@jimalbi]

What about the stability of speed? Wind speed is not constant. I know the attack angle of the blades can be modified, but since the grid has to provide a very stable 60hz, how do you make sure you are always synchronized even under a changing wind? Are those generators providing DC then reconvert it to AC at the right frequence and phase? To my knowledge, there is also a significant loss converting DC to AC... How does that work?

[@spaceghost8995]

They are alternators I would guess.

[@jimalbi]

@@spaceghost8995 They are. But their phases would need to be synchronized or the whole thing would blow up. They don't only need to reach 60Hz, their 3 phases must be synchronized with each other wind turbine.

[@neildahlgaard-sigsworth3819]

Some common errors here: 1. The molecules of air don't have any concept of time - the common time path explanation for lift was debunked by NASA and many other bodies years ago. 2. Bernoulli only deals with the changes along a stream line - Bernoulli cannot explain how a wing can generate life when inverted. It is the shape of the aerofol section that defines how much lift will be generated for a given angle of attack.

[@hardcard254]

lift* aerofoil*

[@0ddSavant]

I might have used the example of the blades of an Airplane propellor - which provides “lift” in the forward direction instead of wings which provides lift in an (basically) upward direction.

[@lachoneu2]

Thank you. Great video.

[@chrisroberts3870]

Not sucked in by the lower pressure. It's pushed in by the higher pressure.

[@vidznstuff1]

Neither. Action/reaction. Push air down, pusher goes up

[@ronjon7942]

Ooooo 3:32 nooooo, the air above and below the airfoil does not have to stay together at the trailing edge, in fact it never does - the airflow above accelerates to a velocity much, much higher than the air below (essentially the forward speed of the aircraft). If you believe the split air has to meet, that would mean the air molecules below the wing would need to 'know' where the molecules above are, and molecules aren't smart like that. The 'equal transit time' hypothesis is not only false, it should be intuitively obvious it's false. For those preferring Bernoulli, air travels over the top of the wing faster than the forward airspeed of the aircraft, resulting in lower pressure at the top of the wing and greater pressure below it. The airflow 'sticks' to the airfoil's curvature because air is a viscous fluid. One way to think about the air accelerating over the greater length of the top surface of the wing (relative to the bottom surface) is that it has to speed up to get out of the way of the slower oncoming air. Back to the beginning of the paragraph, this pressure differential provides an upwards lifting force, making the wing rise as the pressures try to equalize. Bernoulli's equation (ie, the venturi effect) accurately describes the pressure fluctuations of the air around the airfoil, but it is important to conceptualize that an airfoil is NOT one-half of a venturi. Believing it is, is another fallacy, like 'equal transit time' discussed above. As an aside, I remember having a hard time grasping that air accelerating over a curved surface having lower pressure than ambient across that surface. One explanation that stuck with me is: because the air on top is faster than below, it exerts less pressure on the top surface because the air molecules aren't there as long, even though the number of molecules exerting their pressure on the upper wing region remains the same. As weird and unintuitive it may seem, there are certain circumstances, depending upon the angle of attack, when portions of the lower surface of the wing may induce lower pressures (negative pressures, as on the upper surface) than other regions on the bottom. Regardless, when summing up all the pressure fluctuations, and the net effect is a positive pressure difference between the bottom and top of the wing, a lifting force is generated. If Newton's 3rd law is more intuitive, the wing forces the air downward, and the equal and opposite reaction forces the wing to move upward (like your hand in the air outside a window of a car traveling forward fast). There's always a lot of focus on the top side of the airfoil, but the underside also contributes to lift. I was taught to consider both Newton and Bernoulli, and add the underside's contribution to lift to the topside's, but that the top of the wing contributes so much more to the lift force that the bottom's effect can be ignored as noise. Perhaps I didn't understand or heard it differently, but it seems my approach was incorrect in concept but still, as it happened, resulted in a correct answer. It turns out that both approaches are correct and both give the right answer when you do the math - that is, each theory correctly explains lift, independent of the other. Each explanation describes why aircraft fly, but from different perspectives; since both are true, you can pick whichever theory you're most comfortable with.

[@MeaHeaR]

Fascinating

[@while.coyote]

This guy is the best.

[@koenth2359]

I believe the shower curtain sucks in because hot water evaporates and also heats the air, so air density gets lower inside and it rises, so that fresh air is sucked in from below. Anyone tried it with really cold water? Or checked that the sucking immediately stops when stopping the water?

[@johannesnm9706]

I appreciate your content why is there no commercials?

[@DaveBoxBG]

Amazing work! I want to know about solar as well!

[@ylette]

New content!

[@justingreen8572]

What about Vertical Axis Wind Turbines?

[@tomaszworoch]

What I would like to see is comparison of cost of different power generation types and problems of high Green energy in your power grid content for big countries like Denmark or Netherland. They have a lot of Wind and Solar does it generates problems for grid energy?

[@vidznstuff1]

Do you know the difference between an economist and a physicist? One doesn't care about cost, the other doesn't care about physics.

[@tomaszworoch]

@@vidznstuff1 I beg you pardon. Engineer who builds power plants needs to be aware about both the cost and the physics.

[@vidznstuff1]

@@tomaszworoch Wind and solar plants are cheaper than coal and are at parity with methane, despite its glut of supply. Anything else? Fossil fuels are becoming uneconomical for everything. In five years, aircraft and long haul trucking will go electric as the new battery tech comes into production within 3-5 years. "Peaker plants" will also become obsolete in favor of grid batteries and car to grid power artbitrage.

[@tomaszworoch]

@@vidznstuff1 clearly you didn't spot my point about country grid. Clear Solar and Wind power grid have problem of storage. If you count PV generation per kWh it's becoming similar in price to fossil fuels kWh. On case of PV with energy storage well then it's decades before it will be reasonably priced. I would love to see electric planes but to been able to fly on one I do not share your optimistic predictions. It will take longer then a few years

[@Aimless6]

- The 'Energie Wende' in Germany failed. It doubled the price and didn't reduce CO2 emissions at all. Because every Watt of wind power needs a Watt of natural gas power in hot standby to take over when the weather changes. - Denmark is lucky in that they can sell excess power to Germany. - When Germany has excess power, Denmark and the Netherlands don't need it because they have their own wind power. - When the grid operator has to order wind turbines to shutdown, they still get paid for the excess power that wasn't needed. - The grid was designed as a backup for when a plant fails unexpectedly. When a storm passes, ALL wind turbines go from maximum power to zero at the same time. - Most of the wind is near the North Sea, so the grid is abused as a transport network. Forcing the grid operators to juggle frequency and phase on a hourly basis. - The Netherlands is building huge wind parks offshore. Guess who has to pay for the grid connection to those parks.... the tax payers.

[@eschdaddy]

Prof, I was curious if you’re using a mirrored image, or are you writing in reverse from behind a clear board? Either way, thanks for the excellent education!

[@BattleshipAgincourt]

Image is flipped. He's right-handed and his pin is on the opposite side of his coat in 'normal' videos.

[@ShalK423]

Ok I knew it was mirrored but how did the overlay work?

[@eschdaddy]

@BattleshipAgincourt: Could be... I was just hoping he taught himself to write that well backwards. That would be WAY cooler and much more impressive.

[@eschdaddy]

@Shalom Korf: I’m assuming with the lighting that there’s a plexiglass board between him and the camera, with the lighting high above the camera to prevent reflection, then image flipped. I REALLY wish he would’ve been writing backwards, just so he'd be that much cooler!

[@marcelogenesis23]

He explained it a long time ago... camera is in the front... glass panel in his front between

[@elialeiba1344]

And he's bacccck

[@adamnudelman7752]

What about vertical windmills. Does that help with the force differential between the top and bottom blades?

[@matthewcecil8552]

Reruns are ok, but I want you to review fusion in greater detail. Or a video on tidal power generation.

[@johannesnm9706]

Also how about horizontal windmill?

[@nannite]

Quickly checking wikipedia, here is an article explaining that both newton and bernoulli can explain lift. both are valid explanations www.planeandpilotmag.com/article/bernoulli-or-newton-whos-right-about-lift/ The real confusion seems to stem from the oversimplified explanations, which are inadequate (eg the equal transit time explanation)

[@joaquinel]

1) How do acrobat symmetrical wing profiles work? Just momentum? Maybe the angle adds some Bernoulli ? 2) Can engineers engineer a marker/board not to do "quiiiicky quiiiiiick"?

[@aytunch]

Prof, another admired video, thanks:) Can you do Windmill economy just like you did for Nuclear and Solar? is it feasible?

[@laerzzyziz2381]

Woo new content. Thanks prof.

[@jamesmclaughlinprimitivele4587]

Excellent

[@James-zh6nf]

Can you cover the economics of hydro power please?

[@MN-hl7bg]

Thanks!!!!!!!

[@maxheadrom3088]

It's a boomerang! It tends to twist also! Well ... it seems ... a boomerang works because one blade is turning against the linear path while the other is in the same direction - that causes the top to try and turn the boomerang along the axis of the travel path and that causes precession ... and the boomerang comes back to you!

[@davidelliott5843]

That cube law on wind speed affects the average power delivered by the machine. Wind does not blow constantly so the average is about 20% of the rated peak power output. A 10 MW turbine averages about 2MW over a year. A 1000 MW wind array only makes 2000MW over the year.

[@salzgurke42]

A modern offshore Windturbine averages at about 60% of its max output capacity, so a big 12MW WIndturbine outputs an average of about 7.5 MW. And this factor goes up the taller and bigger the Turbines get.

[@uncleogee604]

YES MOAR CONTENT

[@delphaneuxlacroix]

So this is why the extremely cold shower curtain keeps attacking me? Time to invest in a glass shower...

[@DetroitDiesel671]

I love your channel. I'd like to know what engineering is being done to prevent bird strikes. Only when birds of prey are safe from these monstrosities will I begin to attempt to tolerate their noise and blight.

[@tommypetraglia4688]

Latest research shows painting the blades has some postive effect against bird strikes

[@gundachandramouli9865]

Sir,You are different from others.

[@usquanigo]

....except for flying inverted, or symmetrical airfoils...

[@jimmurphy6095]

Symmetrical airfoils mimic the "Farm fan" in that they use sheer brute force to create lift. By using the swashplate Mech, along with the blade tilt, you can create lift regardless of your orientation. I fly a HeliMax R/C Copter , but not well enough to fly inverted yet.