How to approximate WAsP 11 results in WAsP 12
This web page describes what you can do (and what you cannot do) in WAsP 12 to get as close as possible to WAsP 11 results.
Summary
The WAsP Team always recommends using the latest version of WAsP because it is the present implementation of our best knowledge. Therefore, it is not recommended to use WAsP 11.
WAsP 11 workspaces can be opened in WAsP 12, and the import process does not change the results as displayed.
When opened in WAsP 12, the WAsP 11 workspace will be very similar to before, and with the wake model reset to PARK1, it’s as close as can be.
If recalculated in WAsP 12, the results for wind climates will inevitably be at least slightly different – even with the same inputs and using the “Terrain analysis (IBZ, legacy)” as well as legacy-emulating settings.
The differences are the consequence of fixes and improvements to the code, which will affect some cases more than others. Comparing results before and after recalculation may show significant differences in some cases.
Context
WAsP 12 was released in December 2017, replacing WAsP 11. As such, WAsP 11 has been officially unsupported since December 2018 (one year after the release of WAsP 12), and it will one day stop working completely.
However, some WAsP users still need to be able to reproduce WAsP 11 results, and this document describes what you can do (and what you cannot do) in WAsP 12 to get as close as possible to WAsP 11 results.
Version history
There have been several releases of WAsP 12, containing several new features and significant improvements and bringing the latest to version 12.10.112. For more information about the most important new features, please refer to the webpage here:
https://wasp.dtu.dk/software/wasp/whats-new-in-WAsP-12
WAsP 11 has been rebuilt occasionally for operational reasons. The latest build is version 11.06.004, which was compiled in 2023.
Workspace compatibility
A workspace saved from WAsP 11 can be opened in WAsP 12. Depending on the contents of the workspace, dialogs may appear in WAsP 12 which reflect updates to the model structure and extended data requirements. The import process causes all results to be marked as “dirty” (due for recalculation) but does not change the results as displayed.
Hierarchy members imported from WAsP 11 workspaces
IBZ terrain analysis
When you open a WAsP 11 workspace in WAsP 12, the IBZ terrain analyses are created as the type “Terrain analysis (IBZ, legacy)”. These give WAsP 11-identical flow model results.
The newer IBZ terrain analysis, which can be created as the type “Terrain analysis (IBZ)” (not legacy), improves the roughness assessment model and gives different results.
GWCs as input (static)
If a GWC from WAsP 11 is simply imported to WAsP 12 and is not recalculated, then the data are just as they were in WAsP 11. Extra barometric data for calculating air density can be automatically retrieved and inserted, but these do not affect the actual wind climate (wind frequency roses and wind speed distributions for five standard heights above ground level and five roughness classes in 12 wind direction sectors).
The new WAsP 12-specific features of the GWC are not turned on. The “EWA profile model” is selected, with EWA profile values from the WAsP 11 workspace. The geostrophic wind shear model is not used.
Wind turbine generators and AEP calculations
When imported from a WAsP 11 workspace, a WTG has a basic air density correction policy (single production table selected for all sites with no interpolation). In this configuration, the power curve used for AEP calculations is equivalent to WAsP 11.
If the WTG from the WAsP 11 workspace has multiple performance tables, any table selection that was made in WAsP 11 is not preserved when opened in WAsP 12. Instead, the WTG window is marked with a red alert icon. To emulate WAsP 11, the same table needs to be manually selected again in WAsP 12.
A dialog may appear asking about the control system of the WTG. The control system is used when applying an air density correction to the WTG, and the inferred choice should be correct. However, that correction is not being applied when emulating WAsP 11, so the control system makes no difference to the results.
Wake model settings
When the WAsP 11 workspace contains a wind farm, the wake model settings are changed when opening in WAsP 12. WAsP 11 uses the PARK1 model, but the default in WAsP 12 is PARK2, and the new default is automatically applied to existing wind farms. Any non-default wake decay constants set in the WAsP 11 project are discarded.
The wake model can be changed back to match WAsP 11. Select the PARK1 model and “force onshore” and then copy any custom wake decay constant values manually into the settings dialog.
A WAsP 11 workspace in WAsP 12
Opened in WAsP 12, the WAsP 11 workspace will be very similar to before, and with the wake model reset to PARK1, it’s as close as can be.
Unavoidable differences
GWC calculations
In WAsP 12, the GWC calculation model has been updated with fixes and improvements to the code. Therefore, it cannot give the same results as WAsP 11, even if they are close in most cases.
So if you recalculate a GWC from met. station data, using the “Terrain analysis (IBZ, legacy)” as well as the “EWA profile model” with EWA profile values from the WAsP 11 workspace, you will get a different result. For example, here’s a sample case.
WAsP 11:
WAsP 12:
Predicted wind climate calculations (Weibull results)
The same fixes and improvements to the code mean that if you calculate the wind climate for a turbine site using a static GWC imported from WAsP 11, with the “Terrain analysis (IBZ, legacy)”, then the predicted wind climates (A, k, F) will be different (sometimes below the precision threshold to show in the GUI display). This happens even if the inputs are the same.
Wind power density calculations (impact of site-by-site calculation of air density)
In the WAsP 12 user interface, the power density results are calculated according to the hub height, site-specific air density. This means those numbers will not match the WAsP 11 ones, unless all the sites have a hub height air density which matches the value set for the whole project in WAsP 11. That’s only possible if the hubs have the same height A.S.L. and the WAsP 11 project air density setting is set to the appropriate number. In WAsP 12, that setting is removed, and replaced with site-by-site calculation of air density. There is no simple way to set the air density for any or all turbine sites directly in WAsP 12.
AEP calculations
If the air density interpolation is turned off in WAsP 12, then the same power curve is used for each turbine, regardless of air density at the hub height. So the power curve ‘folding’ with the Weibull is as before, but slight differences in A, k and F (see above) give consequent differences in AEP. The differences are larger than those for wind speeds.