Niels Gylling Mortensen

Dear Rachel, Not quite sure what it could be; is it possible that you mail me the workspace (or just the map) to waspsupport@dtu.dk, then I will take a quick look. Best regards, Niels WAsP support

Dear Fierrinho, There seems to be two schools of thought / practices: 1) Shearing up the observed wind climate to hub height at the mast site and then do the flow modelling – which then describes the horizontal change of the wind climate over the terrain. In this case, you assume that the measured shear is representative for the entire wind profile, and the heat flux value will have little influence on the results (as long as the prediction height is the same). 2) Doing the flow modelling directly between the anemometer and the hub height, which then includes both vertical and horizontal extrapolations. For this, one would need an estimate of the heat flux at the site. The choice of heat flux can be validated at the mast site. Best regards, Niels

Dear Alex, Hmm, I don't know exactly what format and rules are applied in the first line of the map file. I will forward your questions to the programmer of the feature. Best regards, Niels WAsP Support

Dear Ismail, Could you mail a sample data file to waspsupport@dtu.dk, then I will take a look at it and report back. Best regards, Niels WAsP Support

Dear Carriv9, Other users have asked for this functionality, i.e. being able to distribute the yearly production over the months in a typical year, or even other periods. We are looking into this, and with our new subscription-based licence and fast-track development initiatives we hope to be able to make a simple tool available soon (2018). As a WAsP user, you will get information about this in a newsletter or on www.wasp.dk. Best regards, Niels

MET data of Malaysia (from NOAA) is measured at 10m. There is no other free data available for us to do the calculation. In that case, if I do calculations with the 10m data, would my calculations become totally invalid? No, the software will certainly extrapolate these measurements for you, but the uncertainty will be higher than if you used a taller mast. Other free data: you can always use the Global Wind Atlas as well, but this also carries a fairly high uncertainty in predictions of single wind turbines and farms, see this presentation: http://orbit.dtu.dk/en/publications/global-wind-atlas--validation-and-uncertainty(7c6ba0d3-49b5-4973-91ce-811c7bdd7ff8).html. Best regards, Niels

SRTM is orographic (elevation) only. There is no roughness information from that radar survey of the world. True, but information on land and water surfaces has been added to the SRTM database. So, if you construct an elevation map from SRTM data using the Map Editor, the map will contain roughness change lines at the coastlines, lakes, large rivers etc. Roughness of the water areas will be 0 m (zero m), and roughness of the land areas is specified by the user. You can then add more land cover classes to this map using the Map Editor, or Google Earth. Best regards, Niels

Dear gtaklis, It is difficult to provide any advice for this combination of software; WAsP 8.4 has not been supported for about 10 years now. Best regards, Niels

Dear Irving, As you write, I have some experience in hotter climates, where it is sometimes required to tweak the heat flux values to get a better fit of the WAsP modelling to the measured profile. However, you have to be careful... many things have to be checked/done first: - mast spec's (position, height of instruments, boom orientation, etc.) - wind measurements (calibration, data quality, missing data, etc.) - elevation map (size, resolution, detail, quality, etc.) - roughness map (size, resolution, roughness values, etc.) - any nearby obstacles or significant mast flow distortion - adjustment of GWC heights to project spec's If these basics are ok, it may be in order to tweak the heat flux values. However, it should be done based on a wind profile analysis as described in the report. This is because the WAsP heat fluxes are not exactly the same as the heat fluxes you can measure / estimate in nature (though they are strongly related). In South Africa, I have used heat flux offset values from -50 to +20 W/m^2, see the Wind Atlas for South Africa (http://orbit.dtu.dk/en/publications/wind-atlas-for-south-africa-wasa-observational-wind-atlas-for-10-met-stations-in-northern-western-and-eastern-cape-provinces(b7c28037-116d-422a-a1d8-450c7050f8c7).html). Note though, that this atlas is still being developed. - You will find that the variation on the unstable side is much smaller than on the stable side. Remember, that the WAsP analysis is for entire years, so even if you think the climate / atmosphere is 'unstable', in many cases it is not so on average over the year. We are working on improving the models so they can use measured or modelled heat fluxes in the future. Best regards, Niels

Dear all, We do have a simple MS Excel tool that will help you make different types of layouts. I will make it available on the web site www.wasp.dk asap. -- Niels, WAsP support

Dear Gyeongil, Regarding issue 1): the reason for the change is that many users took 100 h to mean the "maximum radius or extent of the map", when it was in fact meant as the "approximate radius of the map". It was always understood that you should add a bit to this number. We made this clear by adding 50% (my favorite safety margin). Conclusion: WAsP Best Practice is to add some to the 100 h distance, e.g 50%. Best regards, Niels

Hi Guido, You will also need - a land cover / roughness map of the area(s) - wind turbine power and thrust curves if you want to calculate yields - maybe, information about nearby sheltering obstacles You could take a look in these course notes to see what you need and what you need to do: http://orbit.dtu.dk/en/publications/wind-resource-assessment-using-the-wasp-software-dtu-wind-energy-e0135(259e26f3-1828-4e3f-9c37-17de375cd057).html Best regards, Niels

European Wind Atlas explains: The average seasonal variation of the measured wind speed (full line) and cube of wind speed (dashed line) is shown in the top left graph. All data associated with the same calendar month are averaged and the results plotted at the midpoint in each of the indicated monthly intervals. The unit on the ordinate is ms-1 for mean speeds and m3s-3 for the mean of the cube of the wind speed. Values read from the graph must be multiplied by the scale factor (x1 or x25) given to the right. The continuous curves are obtained by interpolation using a periodic cubic spline. The speed data are also contained in the tables on the station description pages. Full explanations in the European Wind Atlas which you can download from the WAsP home page, see http://www.wasp.dk/News/Nyhed?id=f999e21a-4243-428c-a878-f2268113221c. Download is free of charge :-) Cheers, Niels

The *.lib file _is_ the wind atlas and can be used to predict wind and power at specific sites. The WAsP help file contains a quick start tutorial that explains the basic concepts.

Ok, good! -- Niels, WAsP Support

It is difficult to say based on the info given. Could you mail WAsP *.wwh to waspsupport@dtu.dk for analysis? -- Niels, WAsP Support

Hi Anil, So, your WTG hub center is 2-3H away from the obstacle and at a height of 3-4H; where H is the height of the obstacle. The WAsP obstacle model was not designed for this set-up, where the distance is less than about 5H, see the WAsP help file. Therefore, the model may/will not give realistic results (I doubt it will give any shelter effect at all because of the height of the obstacle relative to the hub height). Alternatively, you can specify the tree line as adding to the roughness of the terrain. However, because of the short distance between turbine site and roughness change line, the effect will likely be negligible. So, in summary, WAsP was not really designed for an obstacle being so close to the turbine. In the real world there may be an effect of the tree line, but WAsP is not likely to pick that up. I think you should take a look in the literature and see if you can find a similar situation, or try to model the tree line with another model. Best regards, Niels WAsP support

Hi, The heat flux settings (and other parameters influencing the wind profile) have been moved from the project level to the Generalised wind climate window. There is now a Profile model tab in thios window, which contains the parameters The heat flux settings should stay as they were when importing an old project, but results will always be due for recalculation because of minor model improvements. Best regards, Niels

Dear dryad, My colleague Ole Rathmann has this answer to your question: "First, in principle we cannot know whether, in a shape file, a roughness change line with Z=0 actually MEANS an elevation of zero or just “nothing” – so the problem cannot be dealt with automatically. However, in MapEditor 11 you may multiple-select a bunch of roughness change lines (different roughness values) but all with z=0, and then use the “Edit line properties” option to deselect the elevation for all of them …, but leaving the individual roughness values unchanged." Hope this helps. Best regards, Niels

Hi Rasmus, My colleague Morten wrote this: "The basic input for WEng is called an observed extreme wind file (*.oewc) and it is generated with the WAsP Climate analyst. You could say that WEng *.oewc files are equivalent to the WAsP *.tab or *.owc files. In WEng projects you can convert your observed extreme wind files (*.oewc) to generate generalized extreme wind climate files (*.rewc), save these to disk, and use them in other WEng projects. Thus, the WEng *.rewc files are equivalent to WAsP *.lib or *.rwc wind atlas files. NB: Please use WACA for WEng2 or WACA2 for WEng3 as the observed extreme-wind file format has changed." So, you should only use the LIB file when exporting data to WAT; and here you will be asked for the file. Hope this helps, Niels

Dear Mengesha, Temperature is less important that the altitude, so you can assume a constant air temperature or a lapse rate of, say, 0.0065 degrees per meter altitude. In any case, the air density will be close to 1.073 for your turbine hub height. Best regards, Niels

Dear Mengesha, Usually, we say that the distance from any site to the border of the map should be max(10 km, 100*h), where h is the height of interest (anemometer or hub). So, the distance should always be at least 10 km, but if the turbine is, say, 120 m high, the distance should be at least 100*120 m = 12 km. I like to add a bit (50% ;-) to this, so would probably make the distance requirement 15-20 km in this case. For many modern masts, turbines and wind farms, the map can then easily be 30-40 km in in both directions. Hope this helps, Niels

Dear Mengesha, Please find my answers below. A1. There are two considerations here: the distance between sites (1) and the different terrain characteristics (2) at the two sites. 1) There is no simple ‘distance rule’; it depends on the climatology of the two sites. If the two sites are influenced by the same weather systems, 10 km could be ok; if the two sites are in very different conditions (say, in mountainous terrain), 10 km could be a problem. So, you need to take a good look at the overall weather systems and circulations, since you only have this one mast. 2) The difference in local land cover (roughness), elevation variations and sheltering obstacles are taken into account by the WAsP models, if specified in the vector map and obstacle description. So, here it is first of all about producing a reliable vector map containing the height contours and roughness change lines. The WAsP help file and web site can help you here; a WAsP course would very helpful too ;-) A2. Not sure what you mean here; I don’t think we use this term… please reformulate question. A3. Yes and No… You can easily make a map and do WAsP calculations for this area based on the 10 m mast. However, given the low height of the mast, the distance to the WF site and the rather large size of the area, the predictions will be associated with some (larger than usual) uncertainty. For project design and preparation, or for design of a measurement campaign, this is probably ok. For reliable wind resource assessment and energy yield predictions, one would have liked a couple of higher masts on the wind farm site itself. A map should in general extend to at least 10 km (in all directions) from any mast or prediction site; if the mast and turbines are very high, the distance should be even larger (say, 100 times their height + 50%). A4. WAsP contains a tool, the Air Density Calculator, which can help you estimate the air density at hub height at your site. A5. WAsP takes the log wind profile as its starting point, but also contains a stability model which uses the land and offshore mean and RMS heat flux values as input. These values are not exactly what you can measure at the site, so the easiest way to spot the stability conditions is to compare the modelled wind profile with measurements at several heights above ground – not possible with your 10-m mast unfortunately. Best regards, Niels

Ok, my name is not Tim ;-) but I can tell you that WAsP (including any WAsP report or script output) will not provide information on the wind farm or turbine AEP over time (hourly, daily, monthly, yearly); only the most probable value of the long-term mean annual energy production. The WAsP team is looking into this, but it will likely not be part of the software for some time to come.

AFAIK, there is no universal standard for this. Measnet, for example, has described the general principles in their "Evaluation of Site specific Wind conditions", see http://www.measnet.com/wp-content/uploads/2012/04/Measnet_SiteAssessment_V1-0.pdf, but not with a lot of detail or examples. Some filtering criteria are described in Annex B though. In addtion to the most simple checks, such as the time stamp integrity (observation interval) and checks for missing records in the data series, here are a few of the things you need to look out for in the raw wind data series: 1. Are there any spikes or sudden drops in the data series? 2. Are there periods of constant data values in the data series? 3. Are there periods of missing data in the data series? 4. Are there any unusual patterns in the data series? 5. Are there any unusual patterns in the polar scatter plot? 6. Do the wind speed time traces follow each other for different anemometers? 7. Do the wind direction time traces follow each other for different vanes? 8. Do the measured and Weibull-derived values of U and P compare well? 9. Does the calm class (0-1 m/s) in the histogram look realistic? 10. and so on and so forth... Hope this helps a little.