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WRF wind modeling compared to WTG production in Denmark

WRF wind modeling compared to WTG production in Denmark. Eller rettere: Sikre at energiproduktions prognosen holder. Per Nielsen EMD International A/S www.emd.dk.

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WRF wind modeling compared to WTG production in Denmark

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  1. WRF wind modeling compared to WTG production in Denmark Eller rettere: Sikre at energiproduktions prognosen holder Per Nielsen EMD International A/S www.emd.dk Maker of WindPRO software suite for wind energy project development. Used by round 80% of all Wind energy calculating people world wide.

  2. WTG production as measure for wind In Denmark we have more than 5000 operating wind turbines – some has been operating more than 30 years Wind turbines is very good wind measurement equipment; mainly while they cover a large wind flow area – and are not so often out of operation as anemometers – and are most often in free heights. 11.800.000 m2 rotor area is operating in DK. This is 262 m2 per km2 land area. If you in US should measure a similar flow area per km2, how many anemometers would this require?

  3. Left; Wind energy index (relative), right; WRF Wind speeds 75m a.g.l. (absolute)

  4. BUT, can we trust the long term variations? I had doubts; DK-index decreases in time relative to WRF based index, round 7% over 15 years:

  5. Then I did several different detailed analyses – below the one that was the “eye opener”: Half the turbines has as average an increase in Wind index Corrected Production (WCP). This is not realistic – turbines do not improve in time!

  6. Comparing the “improving” turbine productions to model data index: The increase comply very well to as well Merra as ConWx (WRF) ratios to DK wind index. We hereby conclude the DK index had a bias of 0.4% per year 2002-12 AND that WRF long term trend could be trusted (at least recent 10y).

  7. But are the data reliable for turbine production calculation? NYSTED Offshore wind farm, more than 10 years operation – calculations looks very promising. But is it good enough? Turbine availability cleaning a challenge!

  8. Zooming in, showing the ratios, illustrates that nothing is perfect: Trends (trend line slope) and standard deviations are possible quality measures. Slopes are almost none, st.dev. shown at right. WRF results seems the best!

  9. Example with many turbines, Djursland Only marginal changes to using the “DK-standard wind” – but the site with most hill impact much better handled with WRF data, probably due to more real wind direction distribution. Only one WRF data set used, cleaned with local terrain/micro scale model, ws scaled 4.5% down. Several improvement options with WRF! Many experimental calculations performed with different data - WRF data gives the lowest st.dev !

  10. Example with very long operation period Average slope of -0.5%/y seen in act./calc. ratio. Is this just turbine degradation, or model data bias 93-98? Note the required scaling differences if using 25m or 75m. The micro scale model handles the height scaling – might be the problem.

  11. Looking at results hour by hour, is although some disappointing One reason for the huge scatter is probably the time deviation between meso scale data and real wind. This problem averaging in time solves.

  12. But as we so far just has seen WRF data as “a mast”, scaling the wind data is needed. A more refined “downscaling” is in development. This might solve the DK scaling needs, but this probably wont solve the German, and especially not the Egypt problems.

  13. Egypt is not the only warm country, where large bias is seen to model data (like NCAR). Variations seem caught reasonable well – but a remarkable bias WRF Measured Merra 12 month moving average

  14. Summary: WRF model data work so far impressing well for wind turbine production calculations in Denmark when aggregating on monthly level. Hour by hour, we are not yet there ! If data has a reliable level long back in time is difficult to say, but at least 15y back, modeled wind seem very consistent to turbine production experience. Scaling required, typically wind speeds must be scaled with 0.95 in DK, but for Germany so far 0.80 is seen needed. Advanced downscaling, connecting Micro – Meso models is in development at EMD (and by many others). Warm countries not handled too well - the wind speed level in high wind speed regions not caught by WRF model. (Input data problem?) What is shown / concluded here is only the tip of the iceberg; we will work intense with WRF in future – I personally believe WRF IS FUTURE in Wind energy applications!

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