Betz's Law

German engineer Albert Betz formulated this law in 1919. It states that a wind turbine can harvest 60% of the available wind energy. This value is not efficiency per se, but a harvest rate, since the unused energy in the flow, which sweeps past the rotor, and the decelerated flow will remain and are not converted.


Beaufort wind force scale.


The wind speed at which a wind turbine (WT) turns off for safety reasons.

Dynamic Pitch Control

Utilising the wind controlled vane, which reacts rapidly to changes in wind direction, the pitch of each wing is actively positioned to the correct angle during the 360 degree rotation, so that the efficiency, and subsequently power production, is maximised.

Feed in Tariff

Feed-in Tariffs (FITs) became available in England, Wales and Scotland on 1st April 2010. Under this scheme, energy suppliers have to make regular payments to householders and communities who generate their own electricity from renewable or low carbon sources such as Photovoltaic (PV) panels and wind turbines.


Certain wind turbine models must stand on a suitable foundation. The exact nature of the foundation is determined by a soil report for each specific location (the softer the soil, the deeper the foundation must be).


The generator of a wind turbine converts mechanical energy into electrical energy. Generators for wind turbines differ from conventional power generators because they supply very fluctuating mechanical power (torque) through the connection. Wind turbines generally use an asynchronous generator.

Hub height

The height of the hub of the wind rotor. The hub is the part of the rotor to which the rotor blades are attached. The prevailing wind conditions at hub height help to determine the energy yield.

Kilowatt hour (kWh)

The kilowatt hour (kWh) is not a power unit but a unit of energy.

Megawatts (MW)

Wind turbines may be measured in Megawatts - 1 MW = 1,000 kW = 1,000,000 watts. By way of comparison, a typical light bulb is 60 watts and 1kW corresponds to 1,359 horsepower.

Offshore wind farms

Wind turbines located at sea.

Pitch control

Pitch control allows the wings of a wind turbine to be adjusted to suit the prevailing conditions.

Reactive power

Reactive power is required for most types of magnetic equipment, such as motors and transformers, and causes reactive losses on transmission facilities. Reactive power is provided by generators, synchronous condensers or electrostatic equipment such as capacitors and directly influences the electric system voltage.


The amount that is paid to a wind turbine owner by an energy supply company, according to the Feed-in-Tariff.

Renewable energy

Energy sources which will be available infinitely into the future - essentially wind, solar, geothermal and tidal. These can either be used directly or indirectly in the production of biomass, wind, hydro and thermal energy.


Reduction of wind speed through obstacles (trees, houses, other wind turbines etc). This creates turbulence, which means that systems can not deliver full power. Shadowing is taken into account when preparing earnings forecasts.

Stall control

In contrast to pitch control, stall control is mainly used on smaller wind turbines. Here, the blades are locked in place and do not adjust during operation - instead, they are designed and shaped to increasingly ‘stall’ the blade’s angle both to maximize power output and to protect the turbine from excessive wind speeds.

Weibull distribution

In order to calculate the mean power delivered by a wind turbine from its power curve, it is necessary to know the probability density distribution of the wind speed. The Weibull distribution method is used for this purpose, simply showing the distribution of the proportion of time spent by the wind within narrow bands of wind speed.

Wind Energy

Wind energy is the kinetic energy of moving air masses in the atmosphere. It is an indirect form of solar energy and is therefore a renewable energy.

Wind Speed

The wind speed is the key parameter for the yield of a wind turbine. It is measured in the wind power industry in meters per second (m/sec). 1m/sec is the equivalent to 3.6 kph or 2.236mph.

Wind Assessments

The wind speed at a site is calculated by experts and compiled in a report, which takes data from site and local weather stations. The assessment of a specific site surrounding obstacles, hills, mountains, trees are also considered. At the end of an opinion is the average wind speed of a location in meters per second at hub height, and the Weibull distribution.