Offshore Wind Data

Discussion of meteorological data.

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Ashenafi.Araya
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Offshore Wind Data

Postby Ashenafi.Araya » Fri Jan 01, 2016 12:39 pm

Hello,

From wind data collected at the National Wind Technology Center meteorological towers (M2, M4 and M5) ,are any one of them taken from OFFSHORE sites? are there freely available OFFSHORE wind data?

Please help

Ashenafi

Jason.Jonkman
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Re: Offshore Wind Data

Postby Jason.Jonkman » Sat Jan 02, 2016 7:48 am

Dear Ashenafi,

The meteorological towers installed at the NWTC (M2, M4, and M5) are on land in complex terrain, far from the ocean. The NWTC does not own meteorological towers installed offshore.

You can find publicly available offshore wind data (granted, not at hub-height of modern utility-scale turbines) from the National Data Buoy Center (NDBC) run by the National Oceanic and Atmospheric Administration NOAA: http://www.ndbc.noaa.gov/. We've used this data to establish a comprehensive metocean data set for offshore wind turbine simulations--see: http://onlinelibrary.wiley.com/doi/10.1002/we.1881/full.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Andy.Clifton
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Re: Offshore Wind Data

Postby Andy.Clifton » Mon Jan 04, 2016 7:34 am

Dear Ashenafi,

The answer to this question really depends on what you want to do.

This link to the paper that Jason provided is probably the best if you want to do turbine simulations.

But, if you want real data, there are some data sets available for offshore winds at turbine hub heights (80-100 m) from towers in the North Sea around Germany. These are the FINO towers at http://www.fino-offshore.de/en/; you'll find links to web pages for each of the towers, and from there you can find out how to get data.

Hope this helps,

Andy
Andy Clifton, Ph.D.
Senior Engineer

Ashenafi.Araya
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Re: Offshore Wind Data

Postby Ashenafi.Araya » Mon Jan 04, 2016 9:26 am

Thank you very much, Jason and Andy. It was very useful information.

My work is basically trying to quantify the impact of wind speed profile models (using the Monin-Obukhov Similarity Theory) on the energy production of large wind turbines at different atmospheric thermal stability conditions.

I wanted to use the offshore wind data to extrapolate hub height wind speed from measured data at 10m and comparing the result with the measured hub height data (up to 90m). I will also need to calculate stability parameters such as the bulk Richardson number and the Obukhov length; and the annual energy production.

I will have a look at the turbine simulation paper as well as the real data from FINO. I haven’t got access to both yet.
For the paper that Jason recommended, my university haven’t subscribed to this publication on the online library yet but I have requested.
I have also requested to access the FINO database and waiting for their reply.

Thank you again!
Ashenafi

Saptarshi.Sarkar
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Re: Offshore Wind Data

Postby Saptarshi.Sarkar » Wed Aug 15, 2018 3:55 am

Hi all,

I trying to use the metocean data provided in https://nwtc.nrel.gov/metocean for my research. However, I'm facing two issues. Firstly and most importantly, I have been trying to match the various pdfs for East Coast data with the plots provided in the paper: https://onlinelibrary.wiley.com/doi/ful ... 02/we.1881 using the parameter values provided in the excel sheet of the database. The problem is, although I can reproduce the exact pdfs for wind speed and wind-wave misalignment, I cannot do the same for significant wave height and peak spectral period using the parameters provided in the excel sheet. The shape of the pdfs look similar but the peak values are different. This makes me think that I'm using the wrong parameter values as I'm using in-built Matlab functions to estimate the pdf values. Also, I have read in the paper (https://onlinelibrary.wiley.com/doi/ful ... 02/we.1881) that for gamma distribution the averaging procedure is different. But, I'm assuming the data provided in the excel file are the average parameter values estimated using the proper technique. I will really appreciate any help in this regard.

The second issue is, I have observed that in the Excel file there are many cells with 'NAN'. I'm assuming these are due to lack of actual field data. So, is there a newer version of data available?

Thank you in advance,
Saptarshi

Jason.Jonkman
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Re: Offshore Wind Data

Postby Jason.Jonkman » Wed Aug 15, 2018 6:50 am

Dear Saptarshi,

I've notified the lead author of the paper you ask about in your post; we'll see if he is able to respond.

Regarding the "NaN"s, yes, these indicate bins where there is a lack of field data. A newer version of the data has not been developed.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Saptarshi.Sarkar
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Re: Offshore Wind Data

Postby Saptarshi.Sarkar » Wed Aug 15, 2018 7:31 am

Thanks a lot. I will wait for his reply.

Saptarshi

Gordon.Stewart
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Re: Offshore Wind Data

Postby Gordon.Stewart » Wed Aug 15, 2018 1:07 pm

Hi Saptarshi,

Good catch. I dug through the old files and realized that the significant wave height and peak spectral period plots that I put in the Wind Energy paper actually were actually both for the 14 m/s wind speed bin, not the 12 m/s as indicated in the paper. I double checked, and gampdf(x,8.8335,0.2605) reproduces the black line in Figure 8 of the paper for significant wave height, and gampdf(x,25.4227,0.2957) reproduces Figure 9 for the peak spectral period. Hopefully that clears up the first point.

The NANs are, as both you an Jason pointed out, from lack of sufficient data in these bins. I used only sites with at least ten years of historical data, and these are the conditions that occurred less than 5 times over those ten years. What I found is that if you are using these metocean conditions to do a fatigue study, then these very rare conditions have an extremely small effect on the total fatigue, so just assigning a probability of zero to these bins is appropriate. Trying to estimate ultimate loads is a lot trickier, and these very unlikely sea states might matter, so be careful there.

Hope this clears up your questions, let me know if you have any more.

-Gordie

Saptarshi.Sarkar
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Re: Offshore Wind Data

Postby Saptarshi.Sarkar » Fri Aug 17, 2018 2:25 am

Hi Gordon,

Thanks a lot, it clears up all my doubts and for going through the hassle of digging out the old files. I'm trying to do a fatigue study and you have in fact answered my doubt regarding assigning the probability to those bins.

Thanks again,
Saptarshi

Saptarshi.Sarkar
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Re: Offshore Wind Data

Postby Saptarshi.Sarkar » Fri Aug 24, 2018 8:43 am

Dear Dr Stewart,

I have a couple more queries if you don't mind. If I want to refine the bins (make the bins smaller in size) can I interpolate between the available data? I have observed that in some columns, especially toward the boundary of the tables the value change abruptly from one cell to another. There is no smooth linear or quadratic pattern followed by the parameters in the end columns. I was wondering if interpolation will be a suitable choice or not.

Are the provided wind speeds at the buoy level? And to get the hub-height wind speed can I simply scale it up using the power law or equivalent?

Thank you,
Saptarshi

Gordon.Stewart
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Re: Offshore Wind Data

Postby Gordon.Stewart » Sat Aug 25, 2018 8:02 am

Hi Saptarshi,

I can't give you a good answer about interpolation of the bins. My instinct says that since the lifetime fatigue is dominated by the more likely bins, the jaggedness at the fringes of the probability space won't have much effect, and interpolating the PDF parameters should be ok to do. However, I would definitely recommend getting a fatigue estimate with the coarse bins, then refining and seeing if there is a difference. In my dissertation, I was interested more in going the other way; making the bins more coarse, and showed that you could go to very large bins and still get a good fatigue estimate, so I am not sure if making the bins smaller will have much effect.

As to the second question, all of the wind speeds in the excel document are scaled using the COARE model mentioned in the wind energy paper from buoy height (which was 5 m for most buoys, but 10 m for a few if i remember correctly) to a 90 meter hub height. I show a plot in the wind energy paper comparing the a few power law exponents to the COARE model that I ended up using.

-Gordie

Saptarshi.Sarkar
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Organization: Trinity College Dublin
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Re: Offshore Wind Data

Postby Saptarshi.Sarkar » Mon Aug 27, 2018 5:06 am

Thank you so much, Dr Stewart. Your clarifications are of great help to me.

-Saptarshi


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