A turbine, like the ones in a wind farm, is a machine that spins around in a moving fluid (liquid or gas) and catches some of the energy passing by. All sorts of machines use turbines, from jet engines to hydroelectric power plants and from diesel railroad locomotives to windmills. Even a child's toy windmill is a simple form of turbine.
The huge rotor blades on the front of a wind turbine are the "turbine" part. The blades have a special curved shape, similar to the airfoil wings on a plane. When wind blows past a plane's wings, it moves them upward with a force we call lift; when it blows past a turbine's blades, it spins them around instead. The wind loses some of its kinetic energy (energy of movement) and the turbine gains just as much. As you might expect, the amount of energy that a turbine makes is proportional to the area that its rotor blades sweep out; in other words, the longer the rotor blades, the more energy a turbine will generate. Obviously, faster winds help too: if the wind blows twice as quickly, there's potentially eight times more energy available for a turbine to harvest. That's because the energy in wind is proportional to the cube of its speed.
Wind varies all the time so the electricity produced by a single wind turbine varies as well. Linking many wind turbines together into a large farm, and linking many wind farms in different areas into a national power grid, produces a much more steady supply overall.
Like the turbines,another key part is the gearbox whose gears convert the relatively slow rotation of the spinning blades into higher-speed motion—turning the drive shaft quickly enough to power the electricity generator.
The generator is an essential part of all turbines and you can think of it as being a bit like an enormous, scaled-up version of the dynamo on a bicycle. When you ride a bicycle, the dynamo touching the back wheel spins around and generates enough electricity to make a lamp light up. The same thing happens in a wind turbine, only the "dynamo" generator is driven by the turbine's rotor blades instead of by a bicycle wheel, and the "lamp" is a light in someone's home miles away. In practice, wind turbines use different types of generators that aren't very much like dynamos at all.
Here's how they work;
A typical wind turbine nacelle is 85 meters (280 feet) off the ground—that's like 50 tall adults standing on one another's shoulders! There's a good reason for this. If you've ever stood on a hill that's the tallest point for miles around, you'll know that wind travels much faster when it's clear of the buildings, trees, hills, and other obstructions at ground level. So if you put a turbine's rotor blades high in the air, they capture considerably more wind energy than they would lower down. (If you mount a wind turbine's rotor twice as high, it will usually make about a third more power.) And capturing energy is what wind turbines are all about.
Since the blades of a wind turbine are rotating, they must have kinetic energy, which they "steal" from the wind. Now it's a basic law of physics (known as the conservation of energy) that you can't make energy out of nothing, so the wind must actually slow down slightly when it passes around a wind turbine. That's not really a problem, because there's usually plenty more wind following on behind! It is a problem if you want to build a wind farm: unless you're in a really windy place, you have to make sure each turbine is a good distance from the ones around it so it's not affected by them.
Disadvantages
At first sight, it's hard to imagine why anyone would object to clean and green wind turbines—especially when you compare them to dirty coal-fired plants and risky nuclear ones, but they do have some disadvantages.
One of the characteristics of a wind turbine is that it doesn't generate anything like as much power as a conventional coal, gas, or nuclear plant. A typical modern turbine has a maximum power output of about 2 megawatts (MW), which is enough to run 1000 2kW electric toasters simultaneously—and enough to supply about 1000 homes, if it produces energy about 30 percent of the time. The world's biggest offshore wind turbines can now make 6–8 megawatts, since winds are stronger and more persistent out at sea, and power about 6000 homes. In theory, you'd need 1000 2MW turbines to make as much power as a really sizable (2000 MW or 2GW) coal-fired power plant or a nuclear power station (either of which can generate enough power to run a million 2kW toasters at the same time); in practice, because coal and nuclear power stations produce energy fairly consistently and wind energy is variable, you'd need rather more. (If a good nuclear power plant operates at maximum capacity 90 percent of the time and a good, brand new, offshore wind farm manages to do the same 45 percent of the time, you'd need twice as many wind turbines to make up for that.) Ultimately, wind power is variable and an efficient power grid needs a predictable supply of power to meet varying demand. In practice, that means it needs a mixture of different types of energy so supply can be almost 100 percent guaranteed. Some of these will operate almost continually (like nuclear), some will produce power at peak times (like hydroelectric plants), some will raise or lower the power they make at short notice (like natural gas), and some will make power whenever they can (like wind). Wind power can't be the only form of supply—and no-one has ever pretended that.
As we've just seen, you can't jam a couple of thousand wind turbines tightly together and expect them to work effectively; they have to be spaced some distance apart (typically 3–5 rotor diameters in the "crosswind" direction, between each turbine and the ones either side, and 8–10 diameters in the "downwind" direction, between each turbine and the ones in front and behind). Put these two things together and you arrive at the biggest and most obvious disadvantage of wind power: it takes up a lot of space. If you wanted to power an entire country with wind alone (which no-one has ever seriously suggested), you'd need to cover an absolutely vast land area with turbines. You could still use almost all the land between the turbines for farming; a typical wind farm removes less than 5 percent of land from production (for the turbine bases, access roads, and grid connections). You could mount turbines out at sea instead, but that raises other problems and costs more. Even onshore, connecting arrays of wind turbines to the power grid is obviously a bigger hurdle than wiring up a single, equivalent power plant. Some farmers and landowners have objections to new power lines, though many earn handsome profits from renting out their land (potentially with a guaranteed income for a quarter of a century), most of which they can continue to use as before.
Advantages
On the plus side, wind turbines are clean and green: unlike coal stations, once they're constructed, they don't make the carbon dioxide emissions that are causing global warming or the sulfur dioxide emissions that cause acid rain (a type of air pollution). Once you've built them, the energy they make is limitless and (except for spare parts and maintenance) free over a typical lifetime of 25 years. That's even more of an advantage than it sounds, because the cost of running conventional power plants is heavily geared to risky things like wholesale oil and gas prices and the volatility of world energy markets.
Wind turbine towers and nacelles contain quite a bit of metal, and concrete foundations to stop them falling over (a typical turbine has 8000 parts in total), so constructing them does have some environmental impact. Even so, looking at their entire operating lifespan, it turns out that they have among the lowest carbon dioxide emissions of any form of power generation, significantly lower than fossil-fueled plants, most solar installations, or biomass plants. Now nuclear power plants also have relatively low carbon dioxide emissions, but wind turbines don't have the security, pollution, and waste-disposal problems many people associate with nuclear energy, and they're much quicker and easier to construct. They're also much cheaper, per kilowatt hour of power they produce: half the price of nuclear and two thirds the price of coal (according to 2009 figures quoted by Milligan et al). According to the Global Wind Energy Council, a turbine can produce enough power in 3–6 months to recover the energy used throughout its lifetime (constructing, operating, and recycling it).
Some of the advantages and disadvantages could be swapped but you get the general idea.
The huge rotor blades on the front of a wind turbine are the "turbine" part. The blades have a special curved shape, similar to the airfoil wings on a plane. When wind blows past a plane's wings, it moves them upward with a force we call lift; when it blows past a turbine's blades, it spins them around instead. The wind loses some of its kinetic energy (energy of movement) and the turbine gains just as much. As you might expect, the amount of energy that a turbine makes is proportional to the area that its rotor blades sweep out; in other words, the longer the rotor blades, the more energy a turbine will generate. Obviously, faster winds help too: if the wind blows twice as quickly, there's potentially eight times more energy available for a turbine to harvest. That's because the energy in wind is proportional to the cube of its speed.
Wind varies all the time so the electricity produced by a single wind turbine varies as well. Linking many wind turbines together into a large farm, and linking many wind farms in different areas into a national power grid, produces a much more steady supply overall.
Like the turbines,another key part is the gearbox whose gears convert the relatively slow rotation of the spinning blades into higher-speed motion—turning the drive shaft quickly enough to power the electricity generator.
The generator is an essential part of all turbines and you can think of it as being a bit like an enormous, scaled-up version of the dynamo on a bicycle. When you ride a bicycle, the dynamo touching the back wheel spins around and generates enough electricity to make a lamp light up. The same thing happens in a wind turbine, only the "dynamo" generator is driven by the turbine's rotor blades instead of by a bicycle wheel, and the "lamp" is a light in someone's home miles away. In practice, wind turbines use different types of generators that aren't very much like dynamos at all.
Here's how they work;
- Wind (moving air that contains kinetic energy) blows toward the turbine's rotor blades.
- The rotors spin around, capturing some of the kinetic energy from the wind, and turning the central drive shaft that supports them. Although the outer edges of the rotor blades move very fast, the central axle (drive shaft) they're connected to turns quite slowly.
- In most large modern turbines, the rotor blades can swivel on the hub at the front so they meet the wind at the best angle (or "pitch") for harvesting energy. This is called the pitch control mechanism. On big turbines, small electric motors or hydraulic rams swivel the blades back and forth under precise electronic control. On smaller turbines, the pitch control is often completely mechanical. However, many turbines have fixed rotors and no pitch control at all.
- Inside the nacelle (the main body of the turbine sitting on top of the tower and behind the blades), the gearbox converts the low-speed rotation of the drive shaft (perhaps, 16 revolutions per minute, rpm) into high-speed (perhaps, 1600 rpm) rotation fast enough to drive the generator efficiently.
- The generator, immediately behind the gearbox, takes kinetic energy from the spinning drive shaft and turns it into electrical energy. Running at maximum capacity, a typical 2MW turbine generator will produce 2 million watts of power at about 700 volts.
- Anemometers (automatic speed measuring devices) and wind vanes on the back of the nacelle provide measurements of the wind speed and direction.
- Using these measurements, the entire top part of the turbine (the rotors and nacelle) can be rotated by a yaw motor, mounted between the nacelle and the tower, so it faces directly into the oncoming wind and captures the maximum amount of energy. If it's too windy or turbulent, brakes are applied to stop the rotors from turning (for safety reasons). The brakes are also applied during routine maintenance.
- The electric current produced by the generator flows through a cable running down through the inside of the turbine tower.
- A step-up transformer converts the electricity to about 50 times higher voltage so it can be transmitted efficiently to the power grid (or to nearby buildings or communities). If the electricity is flowing to the grid, it's converted to an even higher voltage (130,000 volts or more) by a substation nearby, which services many turbines.
- Homes enjoy clean, green energy: the turbine has produced no greenhouse gas emissions or pollution as it operates.
- Wind carries on blowing past the turbine, but with less speed and energy (for reasons explained below) and more turbulence (since the turbine has disrupted its flow).
A typical wind turbine nacelle is 85 meters (280 feet) off the ground—that's like 50 tall adults standing on one another's shoulders! There's a good reason for this. If you've ever stood on a hill that's the tallest point for miles around, you'll know that wind travels much faster when it's clear of the buildings, trees, hills, and other obstructions at ground level. So if you put a turbine's rotor blades high in the air, they capture considerably more wind energy than they would lower down. (If you mount a wind turbine's rotor twice as high, it will usually make about a third more power.) And capturing energy is what wind turbines are all about.
Since the blades of a wind turbine are rotating, they must have kinetic energy, which they "steal" from the wind. Now it's a basic law of physics (known as the conservation of energy) that you can't make energy out of nothing, so the wind must actually slow down slightly when it passes around a wind turbine. That's not really a problem, because there's usually plenty more wind following on behind! It is a problem if you want to build a wind farm: unless you're in a really windy place, you have to make sure each turbine is a good distance from the ones around it so it's not affected by them.
Disadvantages
At first sight, it's hard to imagine why anyone would object to clean and green wind turbines—especially when you compare them to dirty coal-fired plants and risky nuclear ones, but they do have some disadvantages.
One of the characteristics of a wind turbine is that it doesn't generate anything like as much power as a conventional coal, gas, or nuclear plant. A typical modern turbine has a maximum power output of about 2 megawatts (MW), which is enough to run 1000 2kW electric toasters simultaneously—and enough to supply about 1000 homes, if it produces energy about 30 percent of the time. The world's biggest offshore wind turbines can now make 6–8 megawatts, since winds are stronger and more persistent out at sea, and power about 6000 homes. In theory, you'd need 1000 2MW turbines to make as much power as a really sizable (2000 MW or 2GW) coal-fired power plant or a nuclear power station (either of which can generate enough power to run a million 2kW toasters at the same time); in practice, because coal and nuclear power stations produce energy fairly consistently and wind energy is variable, you'd need rather more. (If a good nuclear power plant operates at maximum capacity 90 percent of the time and a good, brand new, offshore wind farm manages to do the same 45 percent of the time, you'd need twice as many wind turbines to make up for that.) Ultimately, wind power is variable and an efficient power grid needs a predictable supply of power to meet varying demand. In practice, that means it needs a mixture of different types of energy so supply can be almost 100 percent guaranteed. Some of these will operate almost continually (like nuclear), some will produce power at peak times (like hydroelectric plants), some will raise or lower the power they make at short notice (like natural gas), and some will make power whenever they can (like wind). Wind power can't be the only form of supply—and no-one has ever pretended that.
As we've just seen, you can't jam a couple of thousand wind turbines tightly together and expect them to work effectively; they have to be spaced some distance apart (typically 3–5 rotor diameters in the "crosswind" direction, between each turbine and the ones either side, and 8–10 diameters in the "downwind" direction, between each turbine and the ones in front and behind). Put these two things together and you arrive at the biggest and most obvious disadvantage of wind power: it takes up a lot of space. If you wanted to power an entire country with wind alone (which no-one has ever seriously suggested), you'd need to cover an absolutely vast land area with turbines. You could still use almost all the land between the turbines for farming; a typical wind farm removes less than 5 percent of land from production (for the turbine bases, access roads, and grid connections). You could mount turbines out at sea instead, but that raises other problems and costs more. Even onshore, connecting arrays of wind turbines to the power grid is obviously a bigger hurdle than wiring up a single, equivalent power plant. Some farmers and landowners have objections to new power lines, though many earn handsome profits from renting out their land (potentially with a guaranteed income for a quarter of a century), most of which they can continue to use as before.
Advantages
On the plus side, wind turbines are clean and green: unlike coal stations, once they're constructed, they don't make the carbon dioxide emissions that are causing global warming or the sulfur dioxide emissions that cause acid rain (a type of air pollution). Once you've built them, the energy they make is limitless and (except for spare parts and maintenance) free over a typical lifetime of 25 years. That's even more of an advantage than it sounds, because the cost of running conventional power plants is heavily geared to risky things like wholesale oil and gas prices and the volatility of world energy markets.
Wind turbine towers and nacelles contain quite a bit of metal, and concrete foundations to stop them falling over (a typical turbine has 8000 parts in total), so constructing them does have some environmental impact. Even so, looking at their entire operating lifespan, it turns out that they have among the lowest carbon dioxide emissions of any form of power generation, significantly lower than fossil-fueled plants, most solar installations, or biomass plants. Now nuclear power plants also have relatively low carbon dioxide emissions, but wind turbines don't have the security, pollution, and waste-disposal problems many people associate with nuclear energy, and they're much quicker and easier to construct. They're also much cheaper, per kilowatt hour of power they produce: half the price of nuclear and two thirds the price of coal (according to 2009 figures quoted by Milligan et al). According to the Global Wind Energy Council, a turbine can produce enough power in 3–6 months to recover the energy used throughout its lifetime (constructing, operating, and recycling it).
Some of the advantages and disadvantages could be swapped but you get the general idea.
