Wind
A wind turbine is a component that converts the kinetic energy of the surrounding airstream into electricity. This model is intended to calculate the electrical power that a wind turbine system produces. The performance of wind turbine systems is dependent on the local environmental conditions such as wind speed and density of air at the height of the systems. An analysis of these conditions is necessary to accurately estimate power output.
The model employs the general kinetic energy equation to calculate the performance characteristics of the horizontal axis wind turbine (HAWT) system. It provides a simple approximation algorithm when the power coefficient, Cp, is available which represents the efficiency of the wind turbine in the wind power extraction from the ambient air stream. It also allows the user to input experimental constants so that the power coefficient can precisely be determined according to the characteristic of the airfoil of the system. As for the vertical axis wind turbine (VAWT) systems, it employs the general mathematical equations for straight-bladed Darrieus-type VAWT systems, which are common to VAWT systems. Various types of VAWT systems such as the Savonius-type and the curved-blade (or Egg-beater) type may be simulated with this same model.
This library includes two different types of dynamic power control: Fixed Speed Fixed Pitch (FSFP) and Variable Speed Fixed Pitch (VSFP). Currently, it does not include an algorithm for modeling pitch control such as Fixed Speed Variable Pitch (FSVP) and Variable Speed Variable Pitch (VSVP). If the control type of the wind turbine is either FSVP or VSVP, the control type of VSFP will be assumed. In addition, constant power generation is assumed when the ambient wind speed is between the rated wind speed and the cut out wind speed, if the user specifies one of the last three options. The model also has the ability to account for transient losses associated with the power produced during dynamic control by a user-specified fraction.
The model does not include detailed algorithms for generators and inverters due to concerns for computational convergence, time, and usability. Instead, all conversion losses of these subsystems are included by applying a user-supplied total system efficiency to the maximum power extraction of the wind turbine. The field of the total system efficiency must be specified by the user.
Power Control
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Default Value: Variable Speed Fixed Pitch
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Typical Range: N/A
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Min & Max: N/A
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Units: Variable Speed Fixed Pitch, Fixed Speed Fixed Pitch
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This input is the type of rotor control for the wind turbine. This protects the system against the overloading for a system with no speed or pitch control and also to maximize the energy yield for the system.
Four different control types are classified in the literature: Fixed Speed Fixed Pitch (FSFP), Fixed Speed Variable Pitch (FSVP), Variable Speed Fixed Pitch (VSFP), and Variable Speed Variable Pitch (VSVP). Currently, FSFP and VSFP types can be modeled in TRACE™ 3D Plus and Energy Plus. The other two types will be modeled as VSFP. If the first FSFP control type is chosen, the model assumes the maximum power at a fixed rotor speed when the power output predicted is greater than the maximum until the rotor speed reaches the maximum wind speed. If one of the last three control options is chosen, the model assumes that the system produces a constant power at the rated wind speed when the wind speed is between the rated wind speed and cut-out wind speed. The default value is Variable Speed Fixed Pitch (VSFP).
Rated Full Load Power
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Default Value: 10,000 W
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Typical Range: 0 to 999 x 1012
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Min & Max: N/A
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Units: HP, kW, W
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Enter the nominal power output of the wind turbine system at the rated wind speed in Watts. Note that the user should input the maximum power of the system with no control, i.e., FSFP control type, can physically produce. Manufacturer’s data also indicates it as peak power or rated capacity. If the local wind speed is greater than the rated wind speed, the model assumes constant power output of this field.
System Efficiency
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Default Value: 75%
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Typical Range: 1 to 100
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Min & Max: N/A
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Units: %
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Enter the overall system efficiency of the wind turbine system. It includes all the conversion losses as well as transient losses during the dynamic control when the ambient wind speed is between the rated wind speed and cut-out wind speed. The user also has the ability to specify delivery losses from the system to the local area such as transmission and inverter inefficiencies.
Total Height
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Default Value: 36 ft [IP], 11 m [SI]
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Typical Range: 0 to 999 x 1012
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Min & Max: N/A
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Units: cm, ft, in, m, mm
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This field is the height of the hub of the HAWT system, or of the pole of the VAWT system. It is necessary to estimate local air density and the wind speed at this particular height where the wind turbine system is installed.
Maximum Tip Speed Ratio
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Default Value: 5
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Typical Range: 0 to 12
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Min & Max: N/A
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Units: Dimensionless Ratio
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This field is the maximum tip speed ratio between the rotor velocity and ambient wind velocity. The rotor speed varies with this ratio to maximize the power output when the rotor control types are variable speed. This field allows the user to adjust the power output from the particular system or to find the optimal tip speed ratio of the system. Optimal tip speed ratio is dependent on the number of blades. This ratio is typically about 6, 5, and 3 for two-bladed, three-bladed, and four-bladed rotor, respectively. For the vertical axis wind turbine, it is smaller than horizontal axis wind turbine, and varies with the chord area. The default and maximum values are 5.0 and 12.0 respectively.
Maximum Power Coefficient
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Default Value: 0.5
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Typical Range: 0 to 0.59
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Min & Max: N/A
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Units: Dimensionless
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This field is the maximum fraction of power extraction from ambient wind. If the user inputs this field, the simple approximation model is assumed. The model simply employs the value of this field into the general kinetic energy equation, so that the power output is obtained. The user can obtain this field with a simple calculation from the power curve published in almost all manufacturers' specifications by using the kinetic energy equation as:
Where
P = power production at the rated wind speed [W]
ρ = density of air [kg/m3]
A = swept area of rotor [m2]
V = rated wind speed [m/s]
Cp = power coefficient
The maximum and default values are 0.59 and 0.35.
Rotor - Blade Characteristics
Number of Blades
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Default Value: 3
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Typical Range: 1 to 100
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Min & Max: N/A
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Units: Integer
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Enter the number of blades of the wind turbine. The azimuth angle of the rotor of the VAWT system is determined by dividing 360 degree by this field so that the model determines the chordal velocity component and the normal velocity component of the system. The default number of blades is 3.
Rotor Type
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Default Value: Horizontal
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Typical Range: N/A
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Min & Max: N/A
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Units: Dimensionless
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Enter the type of axis of the wind turbine. The user specifies either a horizontal axis wind turbine or a vertical axis wind turbine. Each type of wind turbine employs a different algorithm for the calculation of the electrical power output of the wind turbine. The default value is Horizontal Axis Wind Turbine.
Rated Rotor Speed
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Default Value: 130 RPM [IP], [SI]
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Typical Range: 0 to 999 x 1012
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Min & Max: N/A
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Units: rad/s, rpm, rps
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Enter the maximum rotational speed of the rotor at the rated power of the wind turbine. It is used to determine the tip speed ratio of the rotor and relative flow velocity incident on a single blade of the VAWT systems.
Rotor Diameter
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Default Value: 17 ft [IP], 5.2 m [SI]
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Typical Range: 0 to 999 x 1012
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Min & Max: N/A
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Units: cm, ft, in, m, mm
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Enter the diameter of the rotor in meters. Note that this field is not the height of the blade, but the diameter of the perpendicular circle from the vertical pole in the VAWT systems. It determines the swept area of the rotor of the HAWT systems and the chordal velocity of the VAWT systems.
Blade Chord Area
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Default Value: 22 ft2 [IP], 2.08 m2 [SI]
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Typical Range: 0 to 999 x 1012
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Min & Max: N/A
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Units: cm2, ft2, in2, m2, mm2
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Input the blade chord area of a single blade of VAWT system. This value is necessary to determine the net tangential and normal forces of a single blade.
Blade Drag Coefficient
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Default Value: 0.9
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Typical Range: 0 to 999 x 1012
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Min & Max: N/A
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Units: Dimensionless
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This field is the blade drag coefficient for a specific blade. It is for determining the tangential and normal force coefficients with the blade lift coefficient (see next field) so that the model can calculate the power output from the system. The user should be able to obtain this parameter for a specific blade from the manufacturer’s data. This field is only valid for VAWT systems.
Blade Lift Coefficient
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Default Value: 0.05
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Typical Range: 0 to 999 x 1012
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Min & Max: N/A
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Units: Dimensionless
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This field is the blade lift coefficient for a specific blade. It is for determining the tangential and normal force coefficients with the blade drag coefficient (see previous field) so that the model can calculate the power output from the system. The user should also be able to obtain it for a specific blade from the manufacturer’s data. This field is only valid for VAWT systems.
Wind Speed
Rated Wind Speed
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Default Value: 2165 ft/min [IP], 11 m/s [SI]
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Typical Range: 0 to 999 x 1012
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Min & Max: N/A
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Units: cm/s, ft/min, ft/s, km/hr, m/min, m/s, mi/min, mph
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Enter the wind speed that the wind turbine system indicates the peak in the power curve. The system produces the maximum power at this speed and the speed of the rotor is managed based on this wind speed.
Cut in Wind Speed
Default: 591 ft/min [IP], 3 m/s [SI]
Range: 0 - 999x1012
Units: cm/s, ft/min, ft/s, km/hr, m/min, m/s, mi/min, mph
Enter the lowest wind speed where the wind turbine system can be operated. No power generation is achieved as long as the ambient wind speed is lower than this speed.
Cut out Wind Speed
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Default Value: 4,912 ft/min [IP], 25 m/s [SI]
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Typical Range: 0 to 999 x 1012
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Min & Max: N/A
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Units: cm/s, ft/min, ft/s, km/hr, m/min, m/s, mi/min, mph
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Enter the largest wind speed that the turbine will operate in. When the wind speed exceeds this value, the wind turbine system needs to be stopped because of inefficiencies in the system. All systems that have either pitch or speed control must be stopped when the ambient wind speed exceeds this speed. Note that the user should input a wind speed above which physical damage to the system might be caused in the case of a FSFP system. Cut in wind speed appears as extreme/survival/design wind speed in the literature. The system will be turned off when the ambient wind speed is over this speed.
Local Average Wind Speed Height
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Default Value: 164 ft [IP], 50 m [SI]
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Typical Range: 0 to 999 x 1012
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Min & Max: N/A
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Units: cm, ft, in, m, mm
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This field is the height that the user entered local wind speed is measured. The annual average local wind speed input is entered by the user in the site section when placing the wind turbine and is internally recalculated by existing Energy Plus functions at the height of the local station.
The figure below shows the location in TRACE™ 3D Plus where you can enter the local wind speed.
