Morten

Hi Phil, I just asked our Map Editor programmer, who reminded me that roughness consistency checks are optional and may be deactivated under 'Tools' in the main menu on the main Map Editor window. Cheers, Morten

Your assumption is correct.

The main principle is first to compute the two types of statistics mentioned above based on the observations and then to select the A and k parameters which give the same statistics when calculated by the Weibull probability model. This is done for every wind sector. The situations with calm weather need special treatment, since we cannot trust the wind direction sensor when the wind speed is close to zero. Calm data are therefore distributed proportionally over the wind sectors using the frequency of occurrence determined by winds above the calm threshold.

Good morning, Contours with 5-m vertical separation could be a good general choice, but unless you are very pressed for time you should also inspect the result in the map image and maybe make some adjustments. Try to zoom in and check whether the generated contours have lots of parallel line segment in the cells of the original SRTM map. If so, you could probably do with less vertical separation as WAsP will get almost the same height information when it interpolates your contour map. On the other hand, you risk losing information on hill top if you set the vertical separation too low, e.g. to 20m – that is unless you manually add exact spot-height information in the map editor, which actually is recommended. Read more in the http://www.wasp.dk/support-and-services sections called ‘maps’, ‘SRTM-maps’ and maybe also at http://www.wasp.dk/support-and-services/faq#weng__working-with-maps-in-weng The horizontal length scales of the terrain features is also important for the flow at hub height. The near-surface flow will always follow the terrain, but undulations with small horizontal length scales will have less influence on the flow at hub height than undulations with a long length scale. So you might need less vertical resolution lower in a landscape with big round hills. A very large contour map fill will slow down the WAsP map pre-processing. A good tip is to have more resolution near the points of interest than at far distance. You can do this with the map editor, e.g. by inserting a high resolution map for the wind-farm area inside a map generated from SRTM downloads. Click ‘File> Import>SRTM’ in the map editor to open a SRTM download window. This has ‘File location’ at the top from where it is possible to change the SRTM download link or use maps stored locally. The default link is https://dds.cr.usgs.gov/srtm/version2_1/SRTM3/ which point towards version 2 maps. You can also work with version 3 maps, but then you need to register at NASA and log in with a user name before you download with the Map Editor. Read more about this in the Map Editor help file. Cheers, Morten

WAsP is fitting Weibull distributions to data by matching two types of statistics: 1) The mean of the cube of the wind speed = 2) The probability of winds above the observed mean wind speed P_model(u>u1) = P_obs(u>u1) where u1 = This procedure does not guarantee a match of the mean wind speed and the fit is generally less accurate at low wind speeds than at high wind speeds. The focus on the high wind-speed range is intentional, since this is where turbines are operating. Cheers, Morten

Hi, Students at the Danish Technical University (DTU) can learn about WAsP in course 46200 Planning and Development of Wind Farms. This three-week 5 ETCS credit course is held each year in January and it covers the same topics as the WAsP course for wind-energy professionals - plus useful knowledge on wind project economics, grid connection, environmental impacts and IEC site assessments. If you are not a DTU student and can't afford the online course, you should read the WAsP help file section called Quick Start Tutorial. It explains the WAsP user interface and demonstrates how to compose a WAsP project using sample input files installed on your PC together with WAsP. Be sure also to install the programs called WAsP Climate Analyst and WAsP Map Editor. These programs will help you when you need to prepare wind statistics and maps for your own projects in the file formats preferred by WAsP. With best regards, Morten Nielsen

Hi CA1, Thank you for the feedback. While writing these I also saw your email to WAsP support and realized that you might have a problem with the WAsP installation. Still, I will keep this general advice, for other readers at this forum. First it is important that turbine positions and the map inside WAsP apply the same projection and datum. If not, you must either transform the map or the turbine site list. This can be done outside WAsP using either the Map Editor (tools>transform>projection) for the map, or the WAsP Projection Transformer (File>transform XYZ file) for the turbine positions. When you input the aligned data, the turbine positions should display correctly inside WAsP. WAsP needs to know the applied map projection and datum in order to make a translation before displaying the information correctly in Google Earth. You can right-click on the map and select ‘Set map projection’ if the projection or datum is unknown, but sometimes projection is included in the map information coming from the Map Editor. As far as I know WAsP will not try to translate the map relative to the turbine positions, i.e. you can use ‘Set map projection’ to provide missing information on projection and datum but not to fix a difference between map and turbine coordinates. This must be done before you load the data into WAsP as described above. I must admit that I too have observed differences between the turbine positions displayed in Google Earth and turbines visible in the GE satellite images. I am not sure how big these should be before it is alarming, but I think you can expect precision around 10 m. If you choose the right projection but false datum, you may see differences on the order of 100m. If you have checked everything and still see significant offsets, then please send a sample project to WAsP support for inspection. Turbine positions in GE are sometimes displayed by 3D models and sometimes by icons. This depends on the zoom factor. Cheers, Morten

Hi Marcos, There is no export to file option for the 'Windfarm overview' results, but you can copy text to clipboard and then paste it into another program. This is done by clicking somewhere in the table you want to copy and then press Ctrl+C on the keyboard. The columns are separated by TAB characters, which works well with MS Excel. In MS Word the imported data will first appear as text, but you can select all of it and then convert it by selecting 'Insert>Table>Convert Text To Table...' and remember to set a checkmark at 'Seperate Text as TABS'. Cheers, Morten

The Coriolis parameter is proportional to sin(lat) - thus highest with opposite signs at the two hemispheres and zero at the equator. WAsP Engineering applies this parameter for conversions between 'observed', 'geostrophic' and 'generalized' winds, using the so-called geostrophic drag law. In contrast, the longitude is not used in the model.

Hi Gyeongil, Sometimes you can use an error messages to guess what is wrong, but in many cases it is mainly useful for the programmer. The auto-generated text lines are associated with exceptions in the code, i.e. unexpected events which disturbs your calculation in various ways. You often see a chain of exceptions caused by a number of routines calling each other. When you report a problem to WAsP support (using 'Help| Email technical support') it is usually a good idea to copy-paste the error message into your email describing the problem. Another useful approach is to include some test data enabling the programmer to reproduce the problem. Cheers, Morten

The Excel-based layout tool is now awailable at http://www.wasp.dk/dataandtools#wasp-tools__wind-farm-layout-tool

Hi Guido, The uncertainty causes and there estimates are nearly arbitrary and just shown for inspiration. You should try make new estimates for each project, and ideally these should be based on statistical data. Some are easy to find, e.g. the accuracy of anemometers which can be read from instrument manuals or wind-tunnel calibrations test. My colleague Mark Kelly is working on error estimates for flow modelling in WAsP, e.g. on the vertical extrapolation, see http://www.wasp.dk/news/nyhed?id=A7044C06-6F5A-4806-8BFD-97CB44A7F112. Other estimates, like uncertainty related to turbine availability, can be harder to find. For this you need access to data from similar project and consider the maintenance strategy, e.g. what is the service plan, limitation on the site access, access to spare parts etc. With best regards, Morten

You could try to reduce the memory usage following the Fuga help file section 'Further information>Fuga speed and memory usage'. The most important tip is that Fuga consider turbines with different hub heights as distinct turbine types, so it is a bad idea to specify individual hub height if these are on the order of a few centimeters.

This is a known bug in a routine gauging the memory use. It is a simple integer overflow and may happen even though you still have not used all the RAM memory. I already fixed it in the developer version.

Hi Clanker, If you select the single-wake page and display a crosswind profile of the velocity deficit you will usually see some undulations outside the main wake. A slight deficit (actully a speedup) next to the wake might be realistic, but it is hard to believe such effects further away so we think that the undulations are caused by a numerical problem in the progam. This undeciered 'model feature' might explain small errors in sector-wise AEP results. You are welcome to send a test case to WAsP support if you see errors are significant and suspect that something else might be wrong. Cheers, Morten

Hi Nico, I am not quite sure which correction you refer to, but I think the answer must be no. You might adapt wind turbine power curves to local turbulence conditions, but WAsP has no built-in method for this, so you would have to do it externally and use the same power curve for all wind directions. Furthermore, the turbulence predictions are only included in WAsP-CFD, not the traditional IBZ WAsP flow model. Best regards, Morten

Hi vman, A turbine with an IEC classification is strong enough to survive a set of design load cases defined in the IEC standard. The environmental conditions for these load cases are modelled by relatvely simple model scaled by reference velocity, Vref, and reference turbulence intensity, Iref. Thus, a turbine with high Iref is tested by more severe turbulence conditions than one with a low Iref. One of these models is called the normal turbulence model (NTM). It is not a fixed turbulence level but something which depends on wind speed. The IEC standard does not classify the sites, but does have a site assessment procedure. The main principle is that the local conditions must not exceed the conditions assumed in the load cases used for turbine classification. There are several checks to be made. For turbulence we must check that the 90% level of the scattered distribution of turbulence conditions (including wake effects and depending on wind speed) must not exceed the NTM model (however only in a certain wind speed range). There is more information in the WAT help file and the most precise description is of course the IEC 61400-1 standard. Cheers, Morten

Hi Cunhae, WAT is trying to support the terrain assessments in IEC 61400-1, IEC 61400-12-1 and IEC 61400-12-2 and they are all different. Furthermore, there are variations among different editions of these standards, and sometimes it is not always clear how to interpret them. When you say maximum slope and variation, I assume that your question refers to IEC 61400-1. First thing to notice is that according to editions 2 and 3 (but not the coming edition 4) the fitted planes must be forced through the tower base. The WAT help file will tell you how this is done in WAT by a least-square-error minimization. Two alternative sets of reference points can be used: 1) all points in the orthogonal grid map lying inside the segments or 2) new points interpolated to a polar grid. I recomend the first method for high-resolution maps and the second method (interpolation) for low-resolution maps. The fit will generally have a tangential component unless you select the option called 'force slope of fitted plane along sector centreline'. The standard does not specify whether this is needed or not, so I found it best to make it optional. Edition 2 (1999) and the original edition 3 (2005) defined the variation as the maximum distance between the fitted plane and auxilary planes fitted to a small disc at every point of terrain assessment. I suppose the intention was to filter out effect of small terrain features. The rules changed in the ammended edition 3/A1 (2010) so now we check the vertical variation at all points, but only consider the criteria to be failed when exceedance is found for points corresponding to an area larger than 5*sqr(z_hub). The WAT project options will allow you to decide whether you want to calculate the variation as specified in the ammendment or not. I admit that this can be confusing. There are many options to consider, so please consult the WAT help file and the edition of the IEC standard you want to follow. You can also right-click the root element in the WAT object hierarchy and open the project option window, then you can select file>default option for the relevant edition. Best regards, Morten Nielsen

Hello, You need an input file for the wind turbine generator you want to use in your project. The first step is to estimate the average air density for the site, e.g. by the air density calculator under the 'tools' menu in WAsP. Next step is to contact the manufacturer and ask for a power curve and thrust coefficient curve for the turbine operating at the given air density. If they dont supply these data in WAsP format, you launch the WAsP Turbine Editor, also found under the 'tools' menu, type in the turbine information and export the data to the file which can be used in WAsP. With best regards, Morten

Hi, Ct means thrust coefficient and it is defined by the thrust force normaliced by the rotor-swept are, air density and wind speed. It is a function of wind speed and needed for the wake model. You can usually get it from the manufacturere. At the moment the wake model of WAsP only supports horizontal-axis turbines. Regards, Morten

Hi Sinisa, There is no radius involved in these calculations. The terrain elevation grid map is Fourier transformed as input to the flow model which is formulated in Fourier space. A computationally efficient way to calculate terrain gradients is to multiply each Fourier mode by wave number vectors and then find the gradient map by inverse Fourier transformation. Values for specific sites are found by interpolation in this grid map. The flow inclination angle are found as the angle between the vertical and horizontal wind components and it approaches the terrain slope close to the ground. You are right that in general the flow inclination angle should decay in the vertical direction, but there can be local exceptions. The reason is that flow perturbations caused by small terrain features decay faster in the vertical direction that perturbations caused by large terrain features. There is a slide from our WEng course showing this and you can download it from http://wasptechnical.dk/Services/Redirect.aspx?token=8c8d0b3b-769d-4b4f-89aa-6e09aa4cca2b Cheers, Morten

Hi Eduardo, First thing to check is that the format of the first column is set to time and not text. Try to select all cells in the first column except the header. Then right click a cells in the selection, select 'Format cells' from the popup menu, and pick a 'Time' format of your own choice. If this does not help, you are also welcome to send us a test file to our help desk using the e-mail link under 'help' in the WAT main menu. I just remember one more thing which is that your PC must have an Excel installation. Currently WAT is not interpreting the Excel file but launcing Excel and using it to read the data. You should also close the file in Excel while trying to read it in WAT, as otherwise it will be blocked for reading. If this becomes a problem for many users, I should find another solution for a future WAT version. Cheers, Morten

Happy New Year to you too! The best practice is to use an OWC based on observed time series with no prior correction for height differences. WAsP models speedup effects between anemometer positions and turbine nacelle positions and this both includes horizontal and vertical variation. There is a document on WAsP best practice available for download at http://www.wasp.dk/Support-and-services/FAQ#webhelp

Hi Trubert, The format of the WAsP WRG file is explained in the WAsP help file section 'Technical refference| WAsP file formats| Resources grid'. The first line describes the grid layout and the folling lines are data records for each grid point. They have the format - Text string (10 characters) identifying the site/grid point - X-coordinate (easting) of the site [m] - Y-coordinate (northing) of the site [m] - Z-coordinate (elevation) of the site [m] - Height above ground level [m a.g.l.] - Weibull A-parameter for the total distribution [ms-1] - Weibull k-parameter for the total distribution - Power density [Wm-2] or power production [Why-1] - Number of sectors - Frequency of occurrence for sector #1 [%·10] - Weibull A-parameter for sector #1 [ms-1·10] - Weibull k-parameter for sector #1 [·100] - Frequency of occurrence for sector #2 [%·10] - Weibull A-parameter for sector #2 [ms-1·10] - Weibull k-parameter for sector #2 [·100] and so on for all sectors. Your mean wind speeds are suspiciously high, i.e. 14.3 m/s in general and 22.0 m/s in sector 8, according to my check. So you should go back to your WAsP (or WindFarmer?) project and check if there is something wrong. Regards, Morten

Hi Aitor, I was referring to our IEC turbulence simulator, which you can download from http://www.wasp.dk/Software/WAsP-Engineering/IEC-Turbulence-Simulator It is like the software you have with a Windows user interface on top of it. You can choose between the same three spectra as in WAsP engineering - see the table at the top of page 2 in ComspecManual.pdf Best regards, Morten Nielsen