Wind turbine power: factors and prospects

Wind power is a fast-growingrenewable energy source playing a crucial role in the global energy transition. This article examines the factors that influence the performance of wind turbines, ways of improving their performance and how they compare with other renewable energy sources.

Basic principles of wind power generation

Wind turbines work by converting the kinetic energy of the wind into electrical energy. The wind turns the turbine blades, which drive a generator to produce electricity. The efficiency of a wind turbine depends on several factors, including wind speed, location and turbine design.

Factors influencing wind turbine efficiency

  • Wind speed: Wind energy production is strongly influenced by wind speed, as the kinetic energy of the wind increases proportionally to the cube of the speed. Thus, a small increase in wind speed results in a significant increase in energy production.
  • Location : The location of a wind turbine is crucial to optimizing its performance. Sites with strong, regular winds, such as coastal areas or mountain ridges, are more suitable for wind power generation.
  • Turbine design: Wind turbines fall into two main categories: horizontal-axis turbines (HAWT) and vertical-axis turbines(VAWT). HAWTs are the most common and generally more efficient than VAWTs, but VAWTs may be better suited to certain conditions, such as urban areas or locations with turbulent winds. More generally, lower power output is the major drawback of many innovations, such as urban wind turbines or bladeless wind turbines.

How is the power of a wind turbine calculated?

Here’s the basic equation for calculating wind turbine power:

P = 0.5 × ρ × A × V³ × Cp

Where:

  • P is power in watts (W)
  • ρ (rho) is air density in kilograms per cubic meter (kg/m³). Air density varies with altitude and temperature, but a commonly used value is 1.225 kg/m³ at sea level and 15°C.
  • A is the area swept by the wind turbine blades in square meters (m²). This area can be calculated as follows: A = π × (D/2)², where D is the rotor diameter in meters (m).
  • V is the wind speed in meters per second (m/s)
  • Cp is the power coefficient, also known as Betz efficiency, which represents theefficiency with which the wind turbine converts wind energy into mechanical energy. The theoretical maximum power coefficient, determined by physicist Albert Betz in 1919, is around 0.59 (or 59%). However, real wind turbines generally have a power coefficient of between 0.35 and 0.45.

It’s important to note that this formula calculates the theoretical power available in the wind, not the electrical power actually produced by the wind turbine, which will be lower due to mechanical and electrical losses.

The price of wind power

The costs of wind power plants vary according to project size, turbine type, location and other site-specific factors. Here are some examples of wind power installations and estimates of the cost per kilowatt (kW) installed:

  1. Small domestic wind turbine (5 kW capacity): These turbines are typically used to power a single-family home or small business. Installation costs for a domestic wind turbine range from $3,000 to $7,000 per kW installed, or $15,000 to $35,000 for a 5 kW turbine. The efficiency of these turbines is highly dependent on local wind speed and mast height.
  2. Medium-sized onshore wind turbine (2 MW capacity): Medium-sized onshore wind turbines are commonly used in commercial wind farms. The installation cost for a medium-sized onshore wind turbine is generally between $1,300 and $2,200 per kW installed. Thus, for a 2 MW (2,000 kW) turbine, the total cost ranges from $2.6 to $4.4 million. The efficiency of these turbines generally varies between 30 and 45%, depending on wind speed and site conditions.
  3. Large-scale offshore wind turbines (8 MW capacity): Offshore wind turbines are installed at sea and generally have a higher capacity than onshore wind turbines. The installation cost for a large offshore wind turbine is generally between $2,500 and $4,500 per kW installed. For an 8 MW (8,000 kW) turbine, the total cost varies between $20 and $36 million. Offshore wind turbines are generally more efficient than onshore wind turbines, due to the stronger, more regular winds at sea, and can achieve efficiencies of 40-50%.

The most powerful wind turbines

Several manufacturers are developing ever larger and more powerful wind turbines, particularly for offshore applications. Here are a few examples of some of the most powerful wind turbines:

  • GE Haliade-X: General Electric has developed the Haliade-X wind turbine, which is currently one of the most powerful wind turbines in the world. It has a capacity of 13 to 14 MW and a rotor diameter of 220 meters.
  • Siemens Gamesa SG 14-222 DD: Siemens Gamesa also offers a powerful offshore wind turbine, the SG 14-222 DD, with a capacity of 14 MW and a rotor diameter of 222 meters.
  • Vestas V236-15.0 MW : Vestas recently announced the development of the V236-15.0 MW wind turbine, which will have a capacity of 15 MW and a rotor diameter of 236 meters.