What force triggers horizontal wind

How does a wind turbine work?

The construction teams only need one to two days to erect a wind turbine on land. In large turbines, rotors that are on the side facing the wind (windward rotors) have prevailed (as opposed to leeward rotors).

The towers can be erected as a lattice mast, as a concrete tower or in steel construction. Hybrid towers made from a steel-concrete combination are also used. The height depends on the rotor diameter, the wind conditions and the legal requirements. The foundations also vary with the location requirements.

Components of wind turbines

The main components of a wind turbine with a horizontal axis of rotation are the rotor, tower, foundation and nacelle.

How do wind turbines generate electricity from wind?

A certain amount of kinetic energy can be extracted from the wind and converted into electrical energy. The usable kinetic energy increases with the wind speed. Put simply, wind turbines use these physical conditions to generate torque and the rotational movement. Current wind turbines work with the principle of buoyancy like airplanes, helicopters or sailing dinghies, not like square sailors and anemometers. The main parameters for the energy yield are:

  • Wind speed: The wind speed is higher at high altitudes than on the ground (wind shear). For a wind turbine, this means that energy production can be increased to a certain extent by using higher towers.
  • Rotor surface: Rotor blades for wind turbines are similar to the wings of aircraft but, unlike the wing, have a sinuous profile. With the latter, the lift is created by a negative pressure on the upper side of the wing. This force enables it to take off. However, if the angle between the wing and the air flow (angle of attack) is too large, the lift can break off. The air flow separates from the profile and turbulence occurs (stall / stall).

With approx. 59% theoretical maximum efficiency and approx. 40% in operation, wind turbines work very efficiently. The energy source - the wind - is exactly where the wind turbine is. The comparison with other energy conversion systems makes it clear that wind is much more efficient than conventional methods:

  • Diesel generator: max. 35%
  • large steam turbine: max. 40%

The losses during the transport of the fossil fuels to the machine are not even included in the calculation.

Optimal operation and power limitation

The wind energy plants are designed for a defined nominal speed (wind speed from which the maximum electricity production is reached) and a corresponding nominal power (maximum output of the plant at nominal speed). However, the nominal speed is above the average prevailing wind speed.

For optimal operation, the wind turbines must be continuously adjusted to the changing wind conditions. This is done, for example, by rotating the rotor blades around their longitudinal axis and thus adjusting the angle of attack (pitch control / blade angle control). If the wind z. B. weaker, the blades are turned into the wind, which increases the power output.

If the lower limit of the wind speed for economical operation is reached, the system is started up by the control electronics. If the wind speed is too high (approx. 25 m / s), it is switched off to avoid overloading. Another possibility of limiting the power is the targeted stall at increasing wind speeds (stall). In these wind turbines, the angle of the rotor blades cannot be variably adjusted.

However, the profiles are designed in such a way that if the wind is too strong, turbulence occurs on the leeward side of the blades and consequently a break in the flow and lift. In this way the energy consumption of the motor is limited. In variable-speed systems, the generators are able to store energy by increasing the speed and reduce load peaks.

In addition, the entire nacelle can track the wind direction determined by sensors using servomotors, i.e. H. "be rotated.

Energy balance of a wind turbine

During its operation, a wind turbine generates a good 40 to 70 times as much energy as is used for its production, use and disposal (cf. BWE 2010 A-Z). The technologies for energy generation are considered with the help of so-called life cycle analyzes (Life Cycle Assessment, LCA), the "energy balance".

It describes the ratio of the energy input for the manufacture of the system, its operation, transport, dismantling or disposal to the average energy produced by it during the operating time.

If more energy is not consumed for the provision of the wind energy installation than can be obtained through its use, a “positive energy balance” or the ability for so-called “energetic amortization” results. Put simply, the amortization period is the period of time up to which the wind energy installation has "produced" the energy required for production again.

The harvest factor of processes with a positive balance is greater than 1. The factor roughly describes the ratio of the amount of energy gained during the service life to the amount of energy used - d. In other words, how many times does the generation of an energy system exceed the amount of energy required to manufacture the system during its service life.

The harvest factor of a modern wind turbine is on average 35 to 66. There are now more modern wind turbines that are even more efficient and have an even better energy balance.

economics

Wind energy is already a cheap source of electricity if you consider the electricity production costs. They contain the total costs of generating electricity in a power plant over a certain period of time (including investments, raw materials, operation and, in some cases, external costs).

The electricity generation costs of a wind turbine with a nominal output of 3,000 kilowatts at an average location can keep up with the costs of conventional electricity generation over a 20-year period (BWE 2015). The Federal Environment Ministry (BMU) also points out that conventional power plants in particular incur high external costs, for example through environmental or climatic damage caused by the emission of air pollutants when using fossil fuels. In addition, wind turbines are becoming more and more efficient and cheaper. This is related, among other things, to technological and procedural improvements. This is also being accelerated by increasing competition.

The wind market has changed from a supplier to a buyer's market in recent years. The investments for larger wind turbines are higher, but these turbines are more economical. This means that the kilowatt hour of electricity generated becomes cheaper the larger the wind turbine and the better its technology. Since 1990, the price of wind turbines has fallen by more than a third.