air density

[cigdemgazioglu]

Dear Wasp Team,

We know that air density depending on elevation and temperature. WASP 9 can take elevation from the map, where take the temperature factor? In tools menu with air density calculator" can do the calculation but we can not find how will adapt to the project , calculated the value of air density. In that air density affects the production of energy, we want to learn how and where we can define air density parameter?

Thank you

[Duncan]

In WAsP 9, the air density is only used to label a WTG performance table. If you open the window for the WTG hierarchy member you should see that each performance table has an air density property. If there are multiple performance tables, then you can select which one to use for the AEP calculation.

In WAsP 10 (not earlier versions), you can set the air density for a whole project. To do this, right-click on the project icon and select "Edit project configuration". Find the section called 'Ambient climate' (near the bottom of the list). There you can edit the air density.

Note that this changes the displayed power density values for all members of the project. All members are affected in the same way, even though they might be at different altitudes/temperatures: we don't apply any kind of lapse rate automatically.

Note also that change this will not affect calculated *production*, because the air density is a property of the power curve/ performance table selected for the WTG. The program will, however, highlight any power curves which have an air density that does not match the project setting. As well as a message to discuss the problem, the WTG hierarchy member icon is tagged with a small purple warning mark.

This is a new WAsP 10 feature, and we're keen to know whether people find it useful. Would a more explicit and automatic treatment of air density be better? If so, how could it work? Everyone is welcome to make contribute thoughts on the Ideas and Suggestions forum.

[Pedrovozone]

Hi
I have used this function in WAsP and it seems to give out good results.
There are, however, some limitations that I believe could be addressed.
As you say, the air density will not affect the AEP on other than the power curve, so it seems this function works more like an 'alarm' for us to select the correct power curve than anything else. I believe that WAsP could easily select the power curve automatically.
Going a bit further, the air density of some sites are not any of those supplied with the power curves, and so sometimes we need to adjust that to match the power curve, which is not ideal. It would be great if WAsP could just interpolate between two power curves to the air density we have selected.
Finally, if you were to put in place an automatic calculated air density, you would probably need to include a provision to either calculate average air temperature on the Climate Analyst, or to actually calculate air density when there is enough data available (temperature, pressure, and eventually %HR.
Both of these numbers could be translated in the file as a single number (average T or Air density)
An ideal situation would be for wasp to calculate air density at each point of the map based on altitude and the average temperature, but this would probably add a whole other layer of calculations to the program.

just some thoughts, hope they are useful.

[Duncan]

Hello, thanks for your comments. We'll certainly consider a more thorough implementation in our next-but-one-release, and your thoughts will help.

We did consider this question of automatic interpolation of power curves, but we were reluctant to take responsibility for that operation in our code.

If the manufacturer doesn't offer the curve for that air density, then you will need to do it yourself. What we could offer is a way to do that in the turbine editor utility program, but it would then remain an explicit operation which you've invoked rather than WAsP generating the numbers automatically. Does that sound useful?

[Pedrovozone]

Yes, I think it does sound reasonable.
I am certainly sensitive to the idea of you not wanting to be held responsible for changing Manufaturers power curves.