A variety of other factors influence wind turbine power output. These can be divided into two categories: aerodynamic and operational. Aerodynamic impacts are those influences on the aerodynamic performance of the rotor airfoils. The most important aerodynamic impacts are the sources of increased surface roughness of the blades, and the prime cause is dead insects built up on the leading edges of the blades. Also recognized are ultra-violet light degradation of the surfaces of the blades, and air pollution. Installations near highways have reported that turbine blades had been soiled by aerosols from the exhaust of diesel engines powering trucks on the highway.
Operational influences are either external- or control-system sources of sub-optimal operation. External causes include power outages or inadvertent shut-down. Control-system causes include sub-optimal cut-in of the rotor due to anemometer or software error. A common cause of sub- optimal operation of horizontal axis turbines is yaw-error: the misalignment of the rotor to the wind which can happen when variation in wind direction occurs faster than the response rate of the yaw drive. Operational factors are commonly lumped into a percent-loss factor or efficiency factor.
4.2.4.4.
External data file
Type 90 reads the wind turbine performance data from a data file. Table 4.2.4–1 describes the required data in the file. An example is available in "Example\Data Files". In Table 4.2.4–1, the text that must appear literally is printed in bold italics, while the variables that must be provided (mostly numbers) are within brackets <>.
Table 4.2.4–1: Type 90, External data file
line Data Comments
1 WECS_Typ <WECS Type> String (for information only) 2 WECS_REF <origin of data> String (for information only)
3 Len_Unit m Do not edit
4 Spd_Unit m/s Do not edit
5 Pwr_Unit kW Do not edit
6 Ctl_mode <control mode>
Control mode is ONE CHARACTER, and there must be ONE SPACE between "Ctl_mode" and the character. Valid choices: S, P, V (S=stall; P=pitch; V=variable speed) 7 Rotor_Ht <rotor height> Rotor center height, meters
8 Rotor_Di <rotor diameter> Rotor diameter, meters
9 Sensr_Ht <sensor height> Sensor Height for data pairs given here below, meters (often rotor center height) 10 Sher_Exp <wind shear exponent> Power-law exponent for vertical wind profile
11 Turb_Int <turbulence intensity> Turbulence intensity valid for this curve 12 Air_Dens <air density> Power curve air density, kg/m3 13 Pwr_Ratd <rated power> Rated power of the turbine, kW 14 Spd_Ratd <rated wind speed> Rated wind speed, m/s
15 Num_Pair <NP> Number of (wind speed, power) pairs in the file (Max 100) 16 <wind speed 1> <power 1> 1separated) – ALWAYS START AT 0.0 st data pair (wind speed, power) - Free format (space … <wind speed> <power> Additional data pairs
15+
NP <wind speed NP> <power NP> Last data pair. Use maximum 100 points
EXAMPLE
WECS_Typ Bonus 2MW (60) ! Wind Turbine type WECS_REF www.bonus.dk ! Data source
Len_Unit m ! Length unit, must be m (do NOT edit) Spd_Unit m/s ! Speed unit, must be m/s (do NOT edit) Pwr_Unit kW ! Power unit, must be m (do NOT edit) Ctl_mode P ! Control mode (S, P, V)
Rotor_Ht 60.00 ! Rotor center height, meters Rotor_Di 76.0 ! Rotor diameter, meters Sensr_Ht 60.00 ! Sensor Height for curve
Sher_Exp 0.16 ! Power-law exp. for wind profile Turb_Int 0.10 ! Turbulence intensity for this curve Air_Dens 1.225 ! Power curve air density, kg/m3 Pwr_Ratd 2000.00 ! Rated power of the turbine, kW Spd_Ratd 15.00 ! Rated wind speed, m/s
Num_Pair 26 ! Number of data pairs in the file 0 0.00 ! First data pair (wind speed, power) 1 0.00 ! Second data pair - Free format 2 0.00 ! Other data pairs
3 9.6
... ... ! Other data pairs (max 100 total) 24 2000
4.2.4.5. References
Connel J. 1985. A primer on turbulence at the wind turbine rotor. In proceedings of Wind Power 1985, pp. 57-66. Washington DC. American Wind Energy Association.
Connel J. 1988. The wind lumps that bump a rotor. In proceedings of Wind Power 1988, pp. 452- 461. Washington DC. American Wind Energy Association.
Koepll G.W. 1982. Putnam's power from the wind: Second Edition. Van Nostrand Reinhold Company, New-York.
Rohatgi J. and Vaughn N. 1974. Wind characteristics: an analysis for the generation of wind power. Alternative Energy Institute. West Texas A&M university.
Spera, D.A. 1986. Overview of the new ASME performance test code for wind turbines. Proceedings of Joint ASME/IEEE power generation conference, 1986. ASME, New-York
Veers P.S. et al. 1994. User's manual for FAROW: Fatigue and reliability of wind turbine components, Version 1.1. Sandia National Laboratories, Albuquerque, NM, USA.
White F. 1994. Fluid Mechanics, Third Edition. Mc Graw Hill, New-York, USA.
Wilson R.E. and Lissaman P.B.S. 1994. Applied aerodynamics of wind power machines. National Science Foundation, Washington DC, USA.
4.2.5.
Type 94: Photovoltaic array
This component models the electrical performance of a photovoltaic array. Type 94 may be used in simulations involving electrical storage batteries, direct load coupling, and utility grid connections. It employs equations for an empirical equivalent circuit model to predict the current- voltage characteristics of a single module. This circuit consists of a DC current source, diode, and either one or two resistors. The strength of the current source is dependent on solar radiation and the IV characteristics of the diode are temperature-dependent. The results for a single module equivalent circuit are extrapolated to predict the performance of a multi-module array.
For crystalline modules (either single crystal or polycrystalline technology), Type 94 employs a “four-parameter” equivalent circuit. The values of these parameters (not to be confused with formal component PARAMETERS in TRNSYS) cannot be obtained directly from manufacturers’ catalogs. However, Type 94 will automatically calculate them from available data. A second equivalent circuit model involving five mathematical parameters is available for amorphous/thin- film PV modules. Again, the component will determine these values from manufactures’ catalog data. Type 94 also includes an optional incidence angle modifier correlation to calculate how the reflectance of the PV module surface varies with the angle of incidence of solar radiation.
Type 94 determines PV current as a function of load voltage. Other OUTPUTS include current and voltage at the maximum power point along the IV curve, open-circuit voltage, and short circuit current.
4.2.5.1. Modeling options
A number of simulation options are available for the Type 94 Photovoltaic Array. The first of these is the mathematical model used to predict the electrical performance of the array. The “four- parameter” model should be used to for single crystal or polycrystalline PVs. This assumes that the slope of the IV curve at short-circuit conditions is zero. The four-parameter model is enabled whenever zero or a positive value is entered for PARAMETER 18. The second PV model, the “five-parameter model” is intended for amorphous or thin-film PVs. This produces a finite negative slope in the IV characteristic at the short-circuit condition. When a negative value is entered for PARAMETER 18, Type 94 takes this value to be the short-circuit IV slope and enables the five- parameter model. Sections 4.2.5.3 and 0 address the four-parameter model and five-parameter model.
The second option is whether or not the simulation should call the “incidence angle modifier” correlation. This correlation accounts for the increased reflective losses when radiation is incident on the module at large angles. If PARAMETER 16 is a positive value, TRNSYS will not call the incidence angle modifier. In this case, PARAMETER 16 is the value of the transmittance-absorptance product (τα) for all angles of incidence. The angle modifier correlation is enabled when a negative value is entered for PARAMETER 16. The magnitude of PARAMETER 16 is then the τα product for normal incidence; τα for other angles are calculated based on the normal value and an empirical correlation as described in Section 4 of the Mathematical Description.
Finally, the user may choose to enter a value for the module series resistance Rs or to call on Type 94 to calculate Rs from other manufacturers’ data. Type 94 reads the series resistance
directly from PARAMETER 19 whenever a positive value is given. Zero of a negative value indicates that Type 94 should calculate Rs; the magnitude of PARAMETER 19 is irrelevant
4.2.5.2. Nomenclature
β Slope of PV array [degrees]
γ Empirical PV curve-fitting parameter
εg Semiconductor bandgap [eV]
ηc Module conversion efficiency
µIsc Temperature coefficient of short-circuit current [A/K] µVoc Temperature coefficient of open-circuit voltage [V/K] θ Angle of incidence for solar radiation [degrees] τα Module transmittance-absorptance product
ταnormal Module transmittance-absorptance product at normal incidence FLAG Flag for PV convergence promotion algorithm
GT Total radiation incident on PV array GT,beam Beam component of incident radiation GT,diff Diffuse component of incident radiation
GT,gnd Ground-reflected component of incident radiation GT,NOCT Incident radiation at NOCT conditions
GT,ref Incident radiation at reference conditions
I Current
IL Module photocurrent
IL,ref Module photocurrent at reference conditions Io Diode reverse saturation current
Io,ref Diode reverse saturation current at reference conditions
Isc Short-circuit current
Isc,ref Short-circuit current at reference conditions Imp Current at maximum power point along IV curve
Imp,ref Current at maximum power point along IV curve, reference conditions IAM Dimensionless incidence angle modifier
k Boltzmann constant [J/K]
NP Number of modules in parallel in array NS Number of modules in series in array Ns Number of individual cells in module
P PV output power
Pmax PV output power at maximum power point along IV curve
q Electron charge constant
Rs Module series resistance [Ω] Rsh Module shunt resistance [Ω]
Tc Module temperature [K]
Tc,NOCT Module temperature at NOCT conditions [K] Tc,ref Module temperature at reference conditions [K] UL Array thermal loss coefficient
V Voltage
Vmp Voltage at maximum power point along IV curve
Vmp,ref Voltage at maximum power point along IV curve, reference conditions Voc Open-circuit voltage
4.2.5.3.
Mathematical description (4-parameter model)
The four-parameter equivalent circuit model was developed largely by Townsend [1989] and also detailed by Duffie and Beckman [1991]. The model was first incorporated into a TRNSYS component by Eckstein [1990], and much of the code in Type 94 comes from Eckstein’s work. Type 94 employs this model for crystalline PV modules. This model is used whenever TRNSYS PARAMETER 19 (the module’s short-circuit IV slope) is set to zero or a positive value. The four parameter model assumes that the slope of the IV curve is zero at the short-circuit condition:
0
0=
⎟
⎠
⎞
⎜
⎝
⎛
= vdV
dI
Eq 4.2.5-1This is a reasonable approximation for crystalline modules. The “four parameters” in the model are IL,ref, Io,ref, γ, and Rs. These are empirical values that cannot be determined directly through physical measurement. Type 94 calculates these values from manufactures’ catalog data; these calculations are discussed in the following. The four-parameter equivalent circuit is shown in Figure 4.2.5–1.
V
I
R
sI
DI
LFigure 4.2.5–1: Equivalent electrical circuit in the 4-parameter model