Wind Energy

Did you know that one of humanity's oldest forms of methods of generating power is still in use today, and actually provides about a quarter of the UK's electricity? Wind energy was first used by humans as long as 7000 years ago to sail along rivers, which over thousands of years developed into windmill systems to pump water or grind grain. In more recent years, the problem of global warming due to greenhouse gas emissions have led to the rapid development of wind turbines for generating renewable electricity. Modern wind turbines can have blades over 100 meters long with a total height of over 250 meters, and power thousands of homes each! Read on to explore the physics behind wind energy.

Wind energy definition

Wind is made up of moving air molecules. These molecules have mass, which means that wind has kinetic energy. This kinetic energy can be captured and converted to other forms of energy.

Wind energy is a form of solar energy, meaning that it originates from the Sun. The Sun heats the atmosphere unevenly so that the temperature varies at different places. This drives extremely strong convection currents throughout the atmosphere, which is what we feel as wind. The irregularities on the Earth's surface, as well as its rotation, also contribute to these convection currents. This tells us why wind energy is a renewable energy source - because the energy originates from the sun, which will always be there (at least for the lifetime of humanity!).

The sun heats different parts of the atmosphere to different temperatures and this results in convection currents - socratic.

The diagram above illustrates how convection currents are created in the Earth's atmosphere in steps:

• The cooler air in the atmosphere lowers and when it reaches the oceans spreads out, creating a breeze (wind).
• Over the land, it heats up and rises again and this rising air helps to form the clouds.
• As the air rises further it becomes cooler and the process starts again.

This is a very simplified explanation to give you a general idea and the other factors mentioned above also contribute to the convection current.

Wind energy diagram

How do we use the kinetic energy from wind and generate electricity? The most common way is through wind turbines, which use the kinetic energy from the wind to generate electricity.

Modern wind turbines usually consist of three blades held high in the air by a steel tower, wikipedia.

Wind turbines usually consist of three blades mounted on top of a steel tower, as shown in the image above. The top of the wind turbine is often over$100\mathrm{ft}$tall, where the wind speeds are higher than those closer to the ground. The blades on a wind turbine turn in much the same way as an aeroplane is kept in the air. This is by an effect called lift. When the wind blows over the curved side of a turbine blade, a low-pressure air pocket forms on this side. The combined low-pressure effect of the air pockets of each blade creates torque and causes them to turn. The blades also turn due to the force from the wind against the flat sides, but this is a much weaker effect than lift.

The blades on a wind turbine are curved and the air flow over them results in lift. The shape is similar to that of an aeroplane, alternative-energy-tutorials.

The blades on a wind turbine are connected to a transmission shaft which itself is connected to a generator. When the blades turn, the transmission shaft spins and so does the generator, which results in electricity being produced. This is illustrated in the diagram below.

Examples of wind energy

We use the kinetic energy from wind for many purposes in addition to generating electricity. In fact, humans have been harnessing energy from the wind to travel on ships for thousands of years!

Sailing

Sailing boats use the kinetic energy from the moving air molecules of wind to move forward - the wind energy is converted into the kinetic energy of the boat. You might have noticed that when sailing boats are moving through the water, their sails are always curved. The sails are made of a flexible material which forms this shape when inflated by the wind. This curved shape means that in addition to being pushed by the pressure of wind on the sail, the boat is also propelled forward due to the effect of lift - just like the blades on a wind turbine. This effect also allows boats to travel perpendicular to the direction of the wind.

The sails on a sailing boat are use the wind to move the boat, wikipedia.

Pumping water

Wind energy was traditionally used to pump water through windmills, which are similar to wind turbines. This water was then used for watering livestock and for irrigation. A windmill is shown below, it has blades like a turbine but they are a lot wider. This is because they are much closer to the ground where the wind is slower and they need to capture as much wind as possible.

Windmills have wider blades and are lower to the ground compared to wind turbines, pixels.

Advantages of wind energy

There are many advantages of using wind energy instead of some other non-renewable energy resources.

Sustainability

As mentioned earlier, wind energy is a renewable energy source because it originates from the Sun. This means that it will never run out so we can continue to use it forever. Non-renewable resources, such as fossil fuels, are finite resources that will eventually run out. It is vital that we switch to using more renewable sources like wind energy before this becomes a major problem for humanity.

Environmentally friendly

Using wind turbines to harvest wind energy does not harm the environment. There are no greenhouse gas emissions, unlike when fossil fuels. Also, wind turbines do not present a risk to human health or produce waste, as nuclear reactors do for example.

Cost

Using wind energy to generate electricity is one of the most cost-efficient ways of doing so. Wind turbines are quite expensive to initially set up, especially in large numbers, but this is more than made up for over the years by how the wind is completely free! Over the lifetime of a wind turbine, the cost per unit of electricity produced is very low. On the other hand, fuels such as coal and oil need to be constantly extracted from the Earth, meaning these sources of electricity are more expensive over the long term.

Disadvantages of wind energy

There are also some disadvantages of using wind as an energy resource.

Unpredictability

It is clear that energy cannot be constantly produced from wind because there is not always wind to use! Also, wind turbines cannot function when the wind is too fast. This means that wind cannot be used as the main source of power generation for the world because it's availability is too unpredictable.

Another problem with using wind turbines to generate electricity from wind is that there are not many locations suitable for building them. Wind turbines have to be built in places with strong and consistent wind - normally in coastal areas, which are often remote. This means that new power lines have to be built to connect the wind turbines to the national grid, which can be expensive.

Effect on wildlife

Wind energy does not release greenhouse gases like non-renewable energy resources, but it can have a harmful effect on wildlife. Birds and bats do not usually survive if they collide with a rotating wind turbine blade. This can be prevented by carefully planning where wind turbines are built. Also, studies have suggested that painting one of the blades black can reduce the number of bird strikes!