WAsP 12 “tall profile” option: measurements required

[shanewind]

I am currently writing the specification for some new masts that would be for quite tall hub height wind turbines. I am aware that WAsP 12 should have the “tall profile” option in the WAsP project parameters.

I suspect that this will then require inputs from a sonic anemometer(s), or will temperature readings at mast height and close to the ground be sufficient to gauge the temperature profile? I want to ensure that the new masts will have all the required data and instrumentation for the new WAsP version. Any guidance for mast specification would be greatly appreciated.

[elbigkonan]

Hi shanewind,
Yes, as you mentioned the idea is to be able to incorporate further meteorological inputs in WAsP so that we can better predict the climatological wind profile. The ideal scenario would be to be able to input parameters related to the momentum and heat fluxes (time series of them). Thus, ideally if you are able to place a scientific sonic anemometer on your mast and record both fluxes, you will be pointing in the right direction. Another alternative is to record temperatures and wind speeds at two heights (humidity and pressure as well); then there are ways to estimate both fluxes using such measurements.
However, I must say that this is a big step in WAsP and we are working hard on finding out what will be the best way to implement this.
Also, in case you can I recommend you install as many sensors as you can. This will allow you to understand your site and find out the limitations in WAsP and the uncertainties on the WAsP estimates.
Cheers

[shanewind]

Hi

Thanks for the reply. I presume then these are the two minimum alternatives then for an onshore wind site?

1. a top mounted 3D sonic anemometer (recording what exact measurements?)

2. temperature, pressure, relative humidity and wind speed recorded at the same heights for 2 heights; one near the bottom of the mast and one near the top

Any further guidance would be great, just to ensure the measurements will be sufficient for WAsP 12, thanks!

[shanewind]

I presume since a sonic anemometer can record air temperature, there is no need for a top mounted temperature sensor for option 1 (single top mounted 3D sonic anemometer)?

[Mark Kelly]

As "elbigkonan" mentioned above, for an on-shore site, one can get a classic measure of the stability (the Obukhov length) from the heat and momentum fluxes, measured by a sonic anemometer in the surface layer. While the popular alternative to this is to measure vertical temperature gradients, these can cause issues: the lower sensor will fall within the atmospheric surface layer a different fraction of the time than the upper temperature sensor, giving results that are not reliably relatable to temperature fluxes or proven theory. The temperature differences can be used qualitatively, however, e.g. to sort data into un/stable regimes.
Again the sonic also gives a better idea of turbulence, so if you have the money to install more than just the near-surface (10m) sonic, then one higher up can potentially be useful as well (it depends on things such as terrain complexity)...
Our statistical implementation using sonic fluxes in WAsP must be further improved before we release it, as AEP depends not only on the mean wind speed, but also the distribution (Weibull-k).
I would also recommend always adding a dedicated temperature sensor along with each sonic anemometer, because the mean temperature from the 'sonics' can e.g. drift (this does not really affect the fluxes).

[shanewind]

Hi WAsP

Thanks for your reply. Have you any further information in relation to what is required as inputs for WAsP 12 tall profile? The 3D sonic anemometer manufacturers require to know the following:
*what parameters/variables are required to be recorded
*at what sampling frequency is this data required to be recorded (ie. very high frequency in the sonic "Online calculation" @ high frequency, or normal frequency in logger eg @ 1 second frequency)
*what timestep is the data required at
*what manner of data is required ie. timestep average / st. dev / mode of data?
We will need to order our sonic anemometry soon as the masts are due to go up soon, therefore it would be ideal to ensure that the correct sonic anemometer and logger setup is installed to ensure that the data will be useful for use with WAsP 12 tall profile.

Thanks,
Shane