Frequency domain AEP
The 'Frequency domain AEP' task allows the user to define models and settings to use in the energy calculation and to export results, once the calculation has been run.
Settings
Calculation Type: The new calculation is a reimplementation of the classic energy calculation that is used for power time series simulations and flow calibration calculations. You can also choose to use this option when running the frequency domain energy calculation, noting the limitations detailed below. For most calculations, the differences in results between the Classic and New versions of the calculation are negligible (< 0.05%). More significant changes are expected when selecting the close spacing variant of the eddy viscosity wake model due to some bug fixes. The changes are explained in full in the 1.3 Release note - New energy calculation: changes and validation.
Check "Calculate Efficiencies". This will run the energy calculation several times to attempt to quantify turbine interaction effects, the high wind speed hysteresis effect and the effect of wind sector management as efficiencies (a percentage total energy when compared to the gross energy).
Apply curtailment rules to consider the rules set in 'Curtailments' in the energy calculation. If "Calculate Efficiencies" is checked, curtailment efficiencies are quantified and reported separately.
Note
Only curtailment rules based on wind speed and wind direction conditions may be used with the frequency domain AEP calculation
Use the association method to give measured wind speed and direction distributions at measurement sites priority over data simulated by flow models and more advanced wake modelling. This is required for modelling net yield distributions in the Net energy task.
Select the number of direction and speed steps to use in the energy calculation.
Flow and Performance Matrices
Select an output folder for the FPMs (if it doesn't exist it will be created) then check each option desired. FPM Data is exported to text files for all turbines in non-neighbour projects once the energy calculation is complete.
The Flow and Performance Matrix provides detailed results for all individual turbines. Results are available for all turbines in non-neighbour farms that are considered in the calculation. The results are corresponding to the 'Full' yield calculation.
The output is a function of wind speed and direction at the initiation mast of the turbines if the association method is used and when the 'Mast Binning' variant of the output is selected. The 'Turbine Binning' variant is derived from the 'Mast Binning' variant, by multiplying the reference wind speed by the speed-ups from output channel #6 and then rebinning the matrix results to the default integer speed steps. The 'Turbine Binning' results then use the turbine wind speed as reference, but individual turbine results can no longer be directly compared as the reference speeds represent different flow cases. When the association method is not used, then the wind speed is always that of the turbine itself.
Most of channels represent spot values rather than bins. Exceptions are probabilities and turbulence channels as these are based in binned input data (TAB or WTI files). For these channels, the wind speed and direction reference represent the centre of the bin.
| No. | Channel | Units | Description |
|---|---|---|---|
| 1 | Total Wind Farm Electric Power | kW | Total wind farm power output |
| 2 | Turbine Electric Power | kW | As 1 but for individual turbines |
| 3 | Turbine Hub Height Waked Wind Speed | m/s | Incident wind speed including wake effects from other turbines |
| 4 | Turbine Hub Height Ambient Wind Speed | m/s | Hub height wind speed before the addition of wake effects, including speedups derived from the flow model data and effects from the Large Wind Farm Correction |
| 6 | Mast to Turbine Speed Ups | - | Speed up between the mast location and at the turbine location, see chapter 7.1. Corrections from the Large Wind Farm Model are also included |
| 7 | Waked Turbulence at Turbines | % | Incident turbulence intensity, including wake effects from other turbines (Eddy Viscosity wake model only). |
| 8 | Ambient Turbulence at Turbines | % | Wake free turbulence intensity |
| 9 | Probability Distribution | - | Probability distribution of wind speed and direction |
| 10 | Design Turbulence by Wind Speed | - | Design equivalent turbulence estimated with Frandsen method weighted with Wohler coefficient. |
| 11 | Design Turbulence by Wind Speed and Direction | - | Design equivalent turbulence estimated with Frandsen method |
| 15 | Terrain Angle | deg | Slope of terrain measured from the turbine location based on gridded terrain data |
| 30 | Turbine operational | - | The New Energy calculation shows the name of the turbine operational mode active at each wind speed and direction. This considers any sector management criteria and incident wind speed reductions due to wake effects. The Classic energy calculation shows 0 or 1 in the matrix according to whether the turbine is in operation. Shutdown corresponds to 0 while the normal and other operational modes correspond to 1. |
Note
If you defined curtailment rules which cause a shutdown you will get zero turbulence intensity reported in the FPMs for flow cases where your turbines are shutdown.
Feature Differences between Classic and New energy calculation
| Feature | Classic | New |
|---|---|---|
| Power time series calculation | No | Yes |
| Frequency domain energy calculation | Yes | Yes (x2 faster) |
| Direction shifts to sector probabilities (association method) | Yes | No |
| Design equivalent turbulence calculation | Yes | No |
| TurbOPark model | No | Yes |
Differences in FPMs between Classic and New energy calculation
The first wind speed bin center is:
- 0 m/s for the Classic energy calculation
- the midpoint between 0 m/s and the first bin top of the frequency distribution for the New Energy calculation. Most commonly the first bin top is 0.5 m/s which makes the first wind speed bin center 0.25 m/s.
The maximum wind speed reported in the FPM may differ:
- The Classic calculation (and the new calculation without the association method) will calculate all wind speed bins up to the value set in the 'Maximum wind speed for testing'.
- The New calculation with the association method will inspect all the initiating probability distributions and only calculate up to the highest wind speed bin which contains non zero probability to make the calculation faster. The same value is used for all turbines and the maximum speed reported in the FPMs are set to this.
The direction centers of the simulated flow cases may differ depending on the binning of the frequency distribution (FD) inputs:
- The Classic always starts with a flow case centered at 0o, so must re-bin frequency.
- The new energy calculation avoids splitting frequency contributions for 2 adjacent sectors of the input FD. The first direction bin is not guaranteed to center on zero. The flow cases chosen depend on size of the input FD sectors and the number of direction sectors requested. Some examples are shown in the table below:
| FD number of sectors | Number of direction steps in the energy calculation | Sectoring in energy calculation |
|---|---|---|
| 12 30o sectors | 180 | Each FD sector divided in 15 2o sectors which results in the first sector being from [359o, 1o[ and the center being 0o. |
| 12 30o sectors | 360 | Each FD sector divided in 30 1o sectors which results in the first sector being from [0o, 1o[ and the center being 0.5o. |
| 16 22.5o sectors | 240 [see note] | Each FD sector divided in 15 1.5o sectors which results in the first sector being from [359.25o, 0.75o[ and the center being 0o. |
Note
We also require that the number of direction steps in the new energy calculation is divisible by the number of direction sectors in the FD.
The only curtailment type supported in Classic AEP is sector management (where only speed and direction fields are populated) and the active mode must be 'shutdown'. Any deviation from this will cause the rule to be bypassed.