Using the software

[mengesha]

Dear all,
My Master thesis work on “Wind Energy Resource Analysis: A case study of Aysha wind farm” using WAsP so that I need your help and an answer my questions. My questions are as follows with first describing of the site.
No wind measurements have been taken at the proposed turbine site , but data have been collected at a 10m wind measurement. The distance between them is 9.5Km. The site roughness characteristics (some ruggedness) is completely different from the proposed turbine site characteristics (the farm is wide flat surface and sandy soil).
Q1. WAsP calculates the data from the 10m wind measurement need to be analyzed to produce a wind atlas, and then the resulting wind atlas needs to be applied to the proposed turbine site to estimate the wind power. What is the effect of distance b/n them is 9.5km which is very far away from the proposed turbine and roughness characteristics of the 10m wind measurement and proposed turbine sites areas are completely diferent. How can I handle this to make the analysis is better?
Q2. What do you mean by “impose site condition”? It is similar to method for Q1.
Q3. Does WAsP can handle this triangle farm land size area (1/2 * W=30Km* H=37km) based on 10m wind measurement data? What is the size of the rectangular map should extend at minimum and maximum from the site of 10m wind measurement data?
Q4. The calculated air density of this site at 10m height is 1.0809kg/m3 using an average temperature (27.02 oc) (this temperature data is taken from weather station at 2m height and 1.5km away from 10m wind measurement mast) and an altitude 750m). How can I extrapolate (estimate) the air density of the turbine’s hub height in this farm due to not having average temperature and an altitude at hub height to estimate air density?
Q5. I have read from FAQ that WAsP assumes a logarithmic wind speed profile of the atmosphere, but how can I determine this site is stable, not stable or neutral?
Thank you very much for your help!
Mengesha

[Niels Gylling Mortensen]

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

[mengesha]

Dear Niels,
Thank you very much for your help!
i have understood almost all but still i could not understand from A3,"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%)" what do mean this and i need further clarification this statment"if the mast and turbines are very high, the distance should be even larger (say, 100 times their height + 50%)"
Best regards,
Mengesha

[vob]

Dear Mengesha,

I think Niels was quite clear: the map that you need for your calculation should of course include both the mast site and the wind farm site. Furthermore, the map should cover at least a 10 km margin to either side of the combined area around the wind farm and the mast. Usually, you set up your map in such a way that the combined mast/farm area is at the map center.


As an example consider a case where the mast is centered 9.5km south of the southern wind farm border, and the farm shape is a square with 4km boundary length. Then your map should have a north-south extension of 10km + 4km + 9.5km +10km = 33.5km, and an east west extension of 10km + 4km + 10km = 24km.


If your mast and/or your hub heights are very large (100m and above), then the wind conditions at this height are less 'localized' than for, say, a 10m mast, simply because distance between land surface and anemometer/turbine is larger. Therefore, the higher you get, the more you need to take the larger surroundings into account. That's why Niels suggested to replace the standard 10km recommendation by the larger value '100*height + 50%'.


For example, if your hub height is 100m this would translante to '100*100m + 0.5*(100*100m)', i.e. 10km+5km=15km. You should replace each occurence of "10km" in my formulas for the map extension above by this new value, so that the north-south extension would then be 15km + 4km + 9.5km + 15km = 43.5km, and the east-west extension becomes 15km + 4km + 15km = 34km.


Of course, all these margin extents are rules of thumb, so please use your own scrutinity to judge if perhaps an even larger area would be required. The 10km margin should, however, be considered as a minimum value, so even though your mast is only 10m high (beware of the caveats already mentioned by Niels) you should still create a map with 10km margins.


Hope this helps.

[Niels Gylling Mortensen]

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

[mengesha]

Dear Niels,
Thank you very much for your help!
It clears almost all but from an answer A4."WAsP contains a tool, the Air Density Calculator, which can help to estimate the air density at hub height at site"
i got the result using air density calculator at an altitude=750m and average temp=27.02 0c above sea level.However, i want to calculate air density at 70m hub height, the hub height altitude will be 750+70= 820m but how could i get average temperature( i have not data) corresponding to this altitude to calculator air density ?
Best regards,
Mengesha

[mengesha]

Dear Niels,
Thank you very much for your help!
It clears almost all but from an answer A4."WAsP contains a tool, the Air Density Calculator, which can help to estimate the air density at hub height at site"
i got the result using air density calculator at an altitude=750m and average temp=27.02 0c above sea level.However, i want to calculate air density at 70m hub height, the hub height altitude will be 750+70= 820m but how could i determine average temperature( i have not data) corresponding to this altitude to calculator air density ?
Best regards,
Mengesha

[Niels Gylling Mortensen]

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

[mengesha]

Dear all,

I am a student from Addis Ababa University, Ethiopia, and my Msc thesis is wind energy resource analysis using WAsP. Nobody those who have the knowledge by wind energy in this university so please help me these questions below.
Q1. How can i predict turbine hub height?
The wind power density normally increases with increasing hub height. This is because normally the decrease in power density due to the decrease in air density is insignificant compared to the increase in power density due to the increase wind speed. The increased annual energy production (due to increased Wind speed) not justifies the larger investment in a taller Tower.
Q2. I have the data measured at 10m height study site and the calculated turbulence intensity at this height is 0.137. What is the formula can I use to determine the turbulence intensity at hub height after extrapolating this 10m wind speed to hub height? Turbulence intensity is very important to determine a wind turbine class to the site.
Q3. I am trying to select wind turbines are based on the following criteria:
Step 1: First look, by matching them site characteristics very close to wind turbine characteristics for all wind turbines.
Step 2: By making comparisons of different wind turbines to the site such as the capacity factor, annual energy production and cost per KWh for each one, after this, choose the one which have higher capacity factor (CF) and annual energy production(AEP) , and less cost per KWh ($/KWh) will taken.
So my question is: Comparison wind turbines as farm will difficult to me because it needs a lot time and messy. So to make simple, can I use one wind turbine generator from each type of wind turbines? From those who are full fill step1 and then going to step 2 to select one who have best wind turbine.

Best regards,
Mengesha

[mengesha]

Dear all,

i have sent to the manufacturer/ company to get the following wind turbines power curve and thrust coefficient but no body answer me/ give me with long period of time while i am waiting in trouble to do WAsP analysis so if you have or how could i get please give me your hand.
1. Gamesa G80/2000 with hub height of 67m
2. Sany SE8220III with hub height of 70m
Best regards
Mengesha

[cuongies]

Dear all!
In Project Area I have 5 wind measurement masts so i have 5 wind data set(wind speed and wind direction) from the masts. Now i can fill the data set to WASP interface but only one set of data to calculate wind energy for 1 area. How can i fill all of them (5 data set) at the same time to calculate for a area. i think that if we have many data sets, the result for a area will be more axactyly than only one data sets.
Please help me! Thank all of you very much!
Longing for the method of filling the many data sets at the same time!