IEC61400-1 section 11.
This report attempts to bring together all information related to site suitability as described in IEC61400-1 section 11 sections 11.9.2 and 11.9.3.
This report is best viewed in a spreadsheet programme such as Microsoft Excel or LibreOffice.
The General Parameters tab gives the energy capture, wake model and effective TI parameters used in the generation of this report as well as the version of Openwind and the mapping projection used.
Each site layer has its own set of tabs, of which the main one of interest is the Compliance tab.
The first table attempts to summarise the the more detailed results from the following tables as well as answer each point in section 11 of the standard in turn. The columns are:
• Label - the turbine index or label if a label field has been set.
• X (Coord) - the eastings coordinate in meters in the workbook projection.
• Y (Coord) - the northings coordinate in meters in the workbook projection.
• Turbine Type - the make and model of the wind turbine generator (WTG) being considered at each site location.
• Hub Height [m] - the hub height of the turbine.
• Rotor Diam. [m] - the rotor diameter of the turbine.
• Design Class V avg [m/s] - the design average wind speed.
• Iref [%] - the reference turbulence intensity in percent.
• V avg (waked) [m/s] - the mean waked wind speed at each turbine location and hub-height in the presence of the other turbines modelled in this workbook. NB: the reduction in wind speed predicted by the wake model used to estimate annual energy production (AEP) is not necessarily consistent with the wakes modelled after Frandsen as part of Annex E of IEC61400-1.
• Nearest turbine distance [m] - the distance to the nearest other wind turbine from either this or any other currently enabled site layer.
• TI15[%] - the estimated total turbulence intensity (TI) at each turbine at a wind speed of 15 m/s. This is the root-sum-square (RSS) of the ambient plus the wake induced TI. This is given purely for interest and is not considered in the standard.
• Terrain Complexity - either a numeric value between 0 and 1 (edition 3) with 0 representing not complex and 1 representing fully complex, or a classification of N=not complex, L=low complexity, M=medium complexity or H=highly complex.
• Vrated [m/s] (PCWG method) - the rated velocity for this turbine type, calculated according to the power curve working group method for TI adjustment of power curves.
• 0.6*Vrated [m/s] - 0.6 times the rated velocity.
• 1.6*Vrated [m/s] - 1.6 times the rated velocity.
• Vavg < Design (11.9.2a) Thorough - this method compares the cumulative probability of the wind distribution at the site to the design by summing over the interval of Vave to 2.Vave
• Vavg < Design (11.9.2a) Simple - this method uses the formula
• Effective TI < Design (11.9.2b) - this is a strict comparison of the site effective TI at every wind speed to the design NTM curve. Any exceedance will result in a fail which will result in a red cell containing the letter N.
• Is flow inclination OK (11.9.2c) - this compares the inflow angle for every direction at the turbine to the limits +/-8°. Compliance is marked by a 'Y'; noncompliance by an 'N' with a red background. This calculation relies on the presence of one or more inflow angle layers which can be computed from Wind Map if need be.
• 0.05 < Mast shear exponent < 0.25 (11.9.2d) - this compares the wind shear calculated at each turbine to the limits in the standard (and given in the column header). This calculation requires there to be multi-height met mast and/or wind resource grid data available at each turbine location.
• Site Dynamic Pressure < Design Dynamic Pressure (11.9.2e) - for a turbine location to pass this test, either the site average air density at this turbine is less than the design air density or the site air density multiplied by the square of the site average wind speed is less then the design air density multiplied by the square of the design average wind speed.
• Representative TI < Design (11.9.3a) - this test compares the site representative TI to the reference NTM. The representative TI is similar to the effective TI but without any consideration of wakes. It omits the contribution of .
• Vref < Design Or Dynamic Pressure at Vref < Design (11.9.3b) - for a turbine locations to pass this test, either site Vref is less than the design Vref or the site Vref multiplied by the square of the site air density is less than the design Vref multiplied by the square of the design air density.
• Ambient Extreme TI < Design (11.9.3c) - this is the ambient extreme TI. See below.
• Waked Extreme TI (worst case) < Design (11.9.3d) - this is the worst effective TI over all directions. See below.
• Weibull K - the estimated site Weibull K shape parameter for each turbine.
• Max inflow angle [degrees] - the maximum inflow angle value over all directions.
• Min inflow angle [degrees] - the minimum inflow angle value over all directions.
• Vertical shear exponent at mast - the shear exponent calculated from the met mast and/wind resource grid and used in 11.9.2d above.
• Avg air density - the average air density at the turbine, estimated relative to the site air density and elevation and lapsed up or down to the turbine hub height and elevation.
• Vref worst - the maximum estimate from the following four methods:
• Vref (EWTS Davenport) - method taken from European Wind Turbine Standards II.
• Vref (EWTS 'Exact') - method taken from European Wind Turbine Standards II.
• Vref (EWTS Gumbel) - method taken from European Wind Turbine Standards II.
• Vref (Gumbel MIS) - using UL's own algorithm.
• Ve50 (1.4) - maximum Vref multiplied by 1.4 to convert between 10 minute average and 3 second gust. 1.4 is a historical default gust factor and is not recommended where site turbulence data is available.
• Ve50 (met mast gust factor) - maximum Vref multiplied by the 3s gust factor specified at the met mast.
• HWH Shutdowns - the number of high wind hysteresis shutdowns. Requires a time-series energy capture.
• PEL ratio - the pseudo-equivalent loads ratio.
• Weibull A - the site Weibull A parameter.
• Vref Limit - the wind speed limit for the 50 year return max 10 minute wind speed.
For more detail please refer to section 11 of the standard.
IEC61400-1 Section 11.9.3a
The design NTM curves for each turbine type are given first for comparison.
This is the 90th percentile site wind speed standard deviation corresponding to the effective TI for each turbine at each wind speed between 1 and 40 m/s. Please see Annex E of IEC61400-1 edition 4 for more details.
The design NTM curves for each turbine type are given first for comparison.
This is the 90th percentile site wind speed standard deviation corresponding to the representative TI ( ) for each turbine at each wind speed between 1 and 40 m/s. Please see Annex E of IEC61400-1 edition 4 for more details.
IEC61400-1 Section 11.9.3c
The design ETM curves for each turbine type are given first for comparison according to equation 20 of section 6.3.3.4 of IEC61400-1 ed4.
This is the estimated site extreme TI according to the following formula from section 11.3.3 of IEC61400-1 ed4:
Sigma (ETM ambient + max center-wake)
IEC61400-1 Section 11.9.3d
The design ETM curves for each turbine type are given first for comparison according to equation 20 of section 6.3.3.4 of IEC61400-1 ed4 (see section above).
This table gives the standard deviation associated with the maximum single direction effective TI in a waked direction due to a combination of ambient and waked TI.
