Introduction of wind energy
Wind can be used to do work. The kinetic energy of the wind can be changed into other forms of energy, either mechanical energy or electrical energy. Wind energy is the kinetic energy that is present in moving air. When a boat lifts a sail, it is using wind energy to push it through the water. This is one form of work. Farmers have been using wind energy for many years to pump water from wells using windmills like the one on the right. In Holland, windmills have been used for centuries to pump water from low-lying areas. Wind is also used to turn large grinding stones to grind wheat or corn, just like a water wheel is turned by water power. Today, the wind is also used to make electricity.
The amount of potential energy depends mainly on wind speed, but is also affected slightly by the density of the air, which is determined by the air temperature, barometric pressure, and altitude.
Wind turbine
A turbine is a device for converting the energy in a moving fluid into mechanical rotating energy. There are big turbines at the bottom of dams that convert the energy from pressure and velocity in water into rotating mechanical energy to drive huge generators. There are turbines in jet engines and turbochargers that convert the velocity, pressure, and temperature, in engine exhaust gasses into mechanical energy. After going through the turbine the exhaust gas is cooler and has a lower pressure. There are steam turbines that convert the pressure and velocity and high temperature of super-heated steam into mechanical rotating energy to drive electric generators. Wind turbines only take velocity or kinetic energy out of the wind. It's only the kinetic energy of the moving air molecules that we can convert to mechanical energy. A wind turbine is a device for converting the kinetic energy in wind into the mechanical energy of a rotating shaft. Usually that rotating mechanical energy is converted immediately by a generator into electrical energy.
The first law of thermodynamics tells us the energy out of a wind turbine has to equal the energy in. The energy in is the kinetic energy from the wind's velocity and air density. It is not possible to convert all of the wind's kinetic energy into mechanical energy. Some energy must remain in the wind. The "energy out" is the energy converted by the turbine blades into mechanical energy, plus whatever energy is left in the air after it passes through the turbin rotors. Power is how fast we are producing or using a quantity energy. Power has units of energy divided by time. A Watt is a unit a power. It represents one joule of energy transformed every second. A 60 Watt light bulb converts 60 joules of energy every second into light and heat. The formula below shows how to calculate the power in the wind (not the power available to us because we can't get it all).
Power in the wind = (density of air)2×(turbine blade diameter)2×(velocity of wind)3× constant
Notice that the power in the wind depends on the density of the air, the diameter of the turbine blades squared (D times D), and the velocity of the wind to the third power (V times V times V). There is also a constant in there.
Blowing wind spins the blades on a wind turbine -- just like a large toy pinwheel. This device is called a wind turbine and not a windmill. A windmill grinds or mills grain, or is used to pump water. The blades of the turbine are attached to a hub that is mounted on a turning shaft. The shaft goes through a gear transmission box where the turning speed is increased. The transmission is attached to a high speed shaft which turns a generator that makes electricity. If the wind gets too high, the turbine has a brake that will keep the blades from turning too fast and being damaged.
Turbine Efficiency
If the turbine could convert all the wind's power to mechanical power we would say it was 100% efficient. But as you probably know, the real world is never so generous. To even achieve 50% is unlikely, and would be a very efficient machine. A 50% efficient turbine would convert half of the power in the wind to mechanical power.
Benefits of wind energy
Wind energy is an ideal renewable energy. Wind energy is a pollution-free, infinitely sustainable form of energy. It doesn’t use fuel; it doesn’t produce greenhouse gasses, and it doesn’t produce toxic or radioactive waste.
Wind energy is quiet and does not present any significant hazard to birds or other wildlife. When large arrays of wind turbines are installed on farmland, only about 2% of the land area is required for the wind turbines. The rest is available for farming, livestock, and other uses. Landowners often receive payment for the use of their land, which enhances their income and increases the value of the land. Ownership of wind turbine generators by individuals and the community allows people to participate directly in the preservation of our environment. Each megawatt-hour of electricity that is generated by wind energy helps to reduce 0.8 to 0.9 tonnes of greenhouse gas emissions that are produced by coal or diesel fuel generation each year.
Resources
1) http://www.energyquest.ca.gov/story/chapter16.html
2) http://canren.gc.ca/tech_appl/index.asp?CaId=6&PgId=232
3) http://ftexploring.com/energy/wind-enrgy.html
No comments:
Post a Comment