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This is the sixth post in the TIMES Series, where we break down everything about Vortex TIMES. In this one, we look at the mean wind speed: how we validate it, what the results say and how terrain changes them. Check out other posts in the series from the table of contents here.
The mean wind speed of Vortex TIMES has an absolute bias of 5.71 ± 4.72 % across 322 validation points at 272 sites, and a signed bias of 0.003 ± 7.393 %. Bias is the modelled minus the measured mean, relative to the measured mean. It is the first metric of our validation.
We compare the modelled mean with the measured mean over the concurrent period, and give the difference in percent of the measured value. The bias is (modelled − measured) / measured.
To give one value across the 322 points, we either remove the sign before averaging (absolute bias) or keep it (signed bias). The absolute bias measures the size of the error at a typical point; the signed bias shows whether the errors cancel across points.
The validation document states: “For wind resource assessment, it is essential that the mean wind speed for the concurrent period of the observations and TIMES dataset is as accurate as possible” (p. 10). That is why the mean is the first metric we report.
The mean is not enough on its own: a typical rough estimate of energy yield applies the turbine power curve to the wind histogram (p. 11). The wind speed distribution post covers that.
Across the 322 validation points of 272 sites, the absolute bias is 5.71 ± 4.72 % and the signed bias is 0.003 ± 7.393 % (mean ± standard deviation across points).
The signed bias is centred on zero, so over the whole set there is no systematic over- or under-estimation, but its standard deviation of 7.393 % shows that individual sites scatter.
The chart shows the mean wind speed metrics among the others validated: dots are means, whiskers are ± one standard deviation across points, and the whiskers are wide compared with the distance of the dots from zero.
Terrain changes the accuracy. Mean wind speed estimates are generally more accurate for flat and simple sites than for complex onshore sites, and offshore estimates tend to be less accurate (p. 14).
The document gives no per-terrain numbers beyond this text, and the offshore category has only 15 sites. The terrain classes (TCIX) are explained in the validation overview.
Vortex TIMES is a column of data, not one time series: the Vortex Interface delivers any height from 10 to 440 m. To illustrate this, we use one example TIMES point, a coastal site, over 20 complete years; its numbers are not validation results. The chart shows the mean wind speed every 10 m, with values between the 11 native model heights interpolated in ln(height).
The mean wind speed is 6.19 m/s at 10 m, 7.18 m/s at 50 m and 7.56 m/s at 100 m. It reaches 7.79 m/s at 150 m, 7.98 m/s at 200 m and 8.29 m/s at 300 m, and is slightly lower at 440 m (8.24 m/s). A bulk power-law exponent between 30 and 330 m of 0.080 summarises the growth, but the profile is not a perfect power law. The vertical profiles post shows why a single exponent is a limited description.
TIMES Remodeling uses Vortex TIMES as the long-term reference to calibrate your measurements. On the out-of-training period of its validation (176 points), the mean wind speed absolute bias decreased by 65 %, from 5.07 ± 4.63 % to 1.59 ± 2.08 %. The Remodeling overview explains how it works.
Sources: TIMES Technical Details and Validation, Nov 2023, pp. 10, 11 and 14, and the TIMES Remodeling Technical Document, Nov 2024. See also the Vortex TIMES product page.
Across 322 validation points at 272 sites, the Vortex TIMES mean wind speed absolute bias is 5.71 ± 4.72 % and the signed bias is 0.003 ± 7.393 %.
The absolute bias of the Vortex TIMES mean wind speed removes the sign at each point before averaging (5.71 %). The signed bias keeps the sign (0.003 %), so it shows whether TIMES is systematically high or low.
Yes. The Vortex TIMES mean wind speed is generally more accurate for flat and simple sites than for complex onshore sites, and offshore estimates (15 sites) tend to be less accurate.
On the out-of-training period of the Remodeling validation (176 points), TIMES Remodeling reduced the mean wind speed absolute bias of Vortex TIMES by 65 %, from 5.07 ± 4.63 % to 1.59 ± 2.08 %.
Thank you for reading. If you have any questions, feel free to contact us. Explore the entire series here. For pricing options, contact us directly or sign up for a free account on our Vortex Interface. We are open to suggestions about other topics that can be added to the analysis, leave your comments below.
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