Introduction:
Renewable energy is energy generated from natural resources--such as sunlight, wind, rain, tides and geothermal heat--which are renewable (naturally replenished).
A wind generator is a machine that captures the force of the wind when used to produce electricity.
Wind power has been around for the past 30 years or so and its one of the most quickly growing economically renewable energy forms in the world. UK just like many countries has set up a range of wind generators to capture the energy (power) of wind.
Wind energy developments have had a success in which it depends upon the reliability and technical performance of wind turbines.
Wind turbines have different sizes in which the range is in between those that are rated under a kilowatt to the largest turbines in megawatt capacity.
Abstract:
A wind turbine is device equipment that converts aeromechanical energy into mechanical energy and then into electrical energy. In conventional wind turbine generators (WTGs) this is done with a blade assembly, which is rotated by the wind to drive a generator. The generator then converts this rotational motion (energy) into electricity, which then is brought to a connected transmission system. A few numbers of wind turbines set together can be called a power plant, supplying electricity into the grid system.
Air is a fluid (invisible) like any other apart from that its atoms are in gas form rather than of liquid. And when air blows speedily, in the figure of wind, those atoms are moving swiftly. Motion has the meaning of kinetic energy, which can be detained. Wind power is caused by the sun. When the sun heats up a certain area of land, the air around that land mass absorbs some of the heat. At a particular temperature, the hotter air starts to move up very quickly because a given volume of hot air is lighter than an equal volume of cooler air. When the lighter hot air suddenly moves up, cooler air flows in to fill the gap the hot air has left behind. That air swifting to fill in the gap is called wind.
If we put a rotor blade on the way of that wind, the wind will push (force) on it, passing on 'some' its own energy of motion (movement) to the blade. This is how a wind turbine catches energy of the wind.
Below there's a picture of a wind turbine and its different parts (which are explained beneath the picture).
The Wind Power Generator's components are explained below:
Rotor blades - captures wind's energy and convert it to rotational energy of shaft.
Shaft - transfers rotational energy into generator.
Nacelle - 'holder' that holds or contains:
Gearbox - increases speed of shaft between rotor hub and generator.
Generator - uses rotational energy of shaft to generate electricity using electromagnetism.
Yaw controller (not shown) - This device moves rotor to align with direction (path) of wind.
Brakes - This part stops rotation of shaft in case of power overload or system failure.
The Nacelle also holds:
Electronic control unit (not shown in the picture) - monitors system, shuts down turbine in case of malfunction and controls yaw mechanism.
Tower - supports rotor and nacelle and lifts entire setup to higher elevation where blades can safely clear the ground.
Electrical equipment - carries electricity from generator down through tower and controls many safety elements of turbine.
Aerodynamics of a wind turbine blade
"The action of the wind on an aerofoil section is to cause lift - this is what causes airplanes to fly. At the same time, there must be a drag force as the wind travels over the blade.
The resultant of these two forces produces the force (F) on the aerofoil section.
The actual physics of why lift is generated is a lot more complex than simply applying Bernoulli's principle to an aerofoil (if Bernoulli's explanation is the correct one, it doesn't explain why a 747 could fly upside down). A better explanation is to consider the air leaving an aerofoil.
The aerofoil deflects the airflow downwards
Consider a pitched wing moving through stationary air at a constant speed, V. From the point of view of the wing, it is not moving. Rather, the air is rushing by it with net speed V in the opposite direction.
Air is made up of many molecules and atoms that follow Newton's Laws of Motion. Newton's second law says that each molecule hitting the wing experiences acceleration proportional to the force of contact, and inversely proportional to its own mass (Newton's second law)
Newton's third law tells us that the wing experiences a force that is equal in size but opposite in direction to that felt by the molecule (Newton's third law). While an individual collision of a molecule has little effect, putting billions of billions of impacts together each second does have a real effect - known as lift."
Physics behind wind turbine generation - The power of the wind
The kinetic energy of a moving object is given by KE =
Where:
m= mass of moving object
V = velocity of moving object
If the wind velocity remains constant, then the only part that varies with time is the mass.
Power = Rate of kinetic energy
= Work /Time
= ½mV2/ t = ½ x mass flow rate x V2.
Mass of moving air = density x volume of cylinder
= density x Area x length
= r A L
The mass flow rate = mass / time
= r A L / t
Now L / t = Velocity
So mass flow rate = r A V The Continuity Equation
Thus, the power of the wind is given by
P = ½ x mass flow rate x V2.
= ½ x (r A V) x V2.
= ½ r A V3.
Swept Area - A = πR2 (m2) Area of the circle swept by the rotor.
In terms of diameter A = πD2
4
Ï = air density
- At sea level it's about 1.2 kg/m3
- At 2,500 m it's about 1 kg/m3
Wind power in the UK:
Picture below shows the number (roughly) of turbines that has been planted in the UK. It also shows by how many companies in they have been planted. Another thing we can spot in the picture is the places where are targeted for future Wind Power Generators.
As a carbon free source of energy, wind power contributes positively to the UK's effort to reduce our carbon emissions to tackle the threat of climate change so the targets of reducing the CO2 and costs of Wind power energy are explained below:
Targets
The UK has committed itself to working towards a 60% reduction in CO2 emissions by 2050, and the development of renewable energy technologies such as wind is a core part of achieving this aim. UK wind resources are more than enough to meet current renewable energy targets - the generation of 10% of UK electricity from renewable sources by 2010, and an aspirational target of 20% by 2020.
Costs
The generation costs of onshore wind power are around 3.2p/kWh (+/-0.3p/kWh), with offshore at around 5.5p/kWh, compared to a wholesale price for electricity of around 3.0p/kWh. The additional system cost is estimated to be around 0.17p/kWh, when there is 20% wind power on the system. Generation costs are likely to decrease over time as the technology improves, but this will be balanced against increased costs for integrating higher levels of wind generation into the system.
Conclusions:
The most important advantage of using wind power turbines are:
Low CO2 emissions (due to manufacture only)
Quick energy payback (< 1 year)
Low pollution effects
Some people think they look attractive
The wind should never run out
The wind is free, wind farms do not require any fuel.
The land underneath and around the wind turbines can still be used for farming and etc.
And
The most important disadvantages of wind turbines are:
Blades and rotating machinery last around 25 years - refurbished machines can be sold to the third world.
Cyclic stresses over time can lead to premature failure
They take up a lot of space for the power they develop - to give the same power output as a conventional power plant requires around to 25 km2 of area.
They can only generate when the wind blows - back up is needed if they are switched off.
Location - they required a "clean", non disturbed flow of air - best sites are on top of cliffs where the air can be funnelled by the geography of the area.
Not suitable for installation near other buildings or close to other turbines.
They need connecting to the grid system - if it is not close by, there will be additional cost installing suitable cables.
The wind is not always predictable so it could not blow always
The land used for wind turbines are normally costs which could be expensive
It can kill birds because migration flocks tend to like the strong winds so the companies tend not to build them on migration routes. (In which the picture shown below is a wind farm in California in which the blades are sharp, but recently the styles of the blades has changed in which ill explain in the next section.
It can be noisy so they normally would not be built close to residential areas.
The changes that have been made to stop wind turbines killing birds:
In the past couple of decades, turbine designs have changed dramatically. Turbine blades are now solid, meaning no lattice structure to attract birds looking to perch. Also, the blades' surface area is much larger, so they don't have to spin as fast to generate power. Slower-moving blades mean fewer bird collisions.
Ref:
http://www.darvill.clara.net/altenerg/wind.htm
http://www.howstuffworks.com
http://www.wikipedia.com
http://science.howstuffworks.com/wind-turbine-kill-birds2.htm
http://science.howstuffworks.com/windpower2.htm
Wind Energy Explained by J.F. Manwell J.J. Mcgowan A.L. Rogers 2009 2nd edition ISBN: 978-0-470-01500-1
http://www.4physics.com/phy_demo/tilted-wing.ht
University Of Nottingham Electrical & Renewable Energy
http://www.sd-commission.org.uk/publications/downloads/Wind_Energy_NovRev2005.pdf
