TRANSCRIPTS


This means, unfortunately, that the efficiency will be low, which makes them almost useless.


Why is the efficiency low if the tip speed is low?


Well, we know from Newton’s second law that forces come in pairs – ‘every action has an equal and opposite reaction’. Now, as the air passes the wind turbine blades, it exerts a force on the blades, which results in a torque which turns the blades. However, the opposite is also true – the blades exert an equal and opposite torque on the air. If the blades are rotating slowly, there will be a high reaction torque, which will result in a large swirling cylinder of air behind the turbine, which represents lost energy. Have a look at the book by Dixon, which gives a description of this.


To recap, so far we’ve looked at the maximum limit for power extraction for any kind of wind power device. We’ve also discussed briefly why most modern turbines have high tip speed ratios. Now, there are so many things I could talk about – we could go into real detail regarding the aerodynamics of wind turbine blades, but I would rather look briefly at four other issues associated with turbine design, so let’s go on to that.


Unit 11, Lesson 11.2, Exercise F ≤2.18


As an aside, some people say that wind turbines can be used in every kind of environment, including urban locations. However, in my view, these turbines are usually very poor. The data shows that, in these locations, the wind is very gusty, or completely blocked by other buildings. This means, unfortunately, that the efficiency will be low, which makes them almost useless.


Unit 11, Lesson 11.2, Exercise G ≤2.19


Extract 1 But in view of the world’s need for cleaner, renewable sources of electricity, wind turbines have become a feature of modern power generation …


Extract 2


… and MacKay, in his excellent analysis of sustainable energy options, has no doubt that wind power will form a significant part of the answer to our future energy needs.


Extract 3


Don’t misunderstand me. I don’t want to imply that only engineering factors affect the widespread use of wind turbines.


Extract 4


There are many other factors related to public opinion, such as the impact on wildlife, and the visual effect on the environment. To some degree, I think engineers must take into account these aspects, but in this lecture, I am only going to consider design.


Extract 5


First of all, it is fair to say that the higher the wind speed, the more energy can be extracted.


Extract 6 But there is an optimum point at which the maximum energy can be extracted. It turns out that this theoretical limit is just under 60% … Let me reiterate: it is impossible to build a wind energy extraction device that converts more than 60% of the energy in the wind.


Extract 7


Not only that, but real-world conditions limit the power conversion even more.


Extract 8 Real wind turbines suffer further losses with respect to real-world conditions, …


Extract 9


To understand this, we need to talk about an important number called the tip speed ratio, that is to say, the ratio between the speed at the tip, or end, of the wind turbine blades and the oncoming wind speed.


Extract 10


If the blades are rotating slowly, there will be a high reaction torque, which will result in a large swirling cylinder of air behind the turbine, which represents lost energy. Have a look at the book by Dixon, which gives a description of this.


Unit 11, Lesson 11.3, Exercise A ≤2.20 electrical 'generator elec'tricity generation fibre-optic 'sensors fixed 'frequency maximum 'energy technical 'aspects 'turbine power 'wind turbine


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