Journal cover Journal topic
Wind Energy Science The interactive open-access journal of the European Academy of Wind Energy
Wind Energ. Sci., 1, 115-128, 2016
https://doi.org/10.5194/wes-1-115-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research articles
24 Aug 2016
Year-to-year correlation, record length, and overconfidence in wind resource assessment
Nicola Bodini1,2, Julie K. Lundquist1,3, Dino Zardi2, and Mark Handschy4,5 1Department of Atmospheric and Oceanic Sciences, University of Colorado Boulder, Boulder, Colorado, USA
2Department of Civil, Environmental and Mechanical Engineering, University of Trento, Trento, Italy
3National Renewable Energy Laboratory, Golden, Colorado, USA
4Enduring Energy, LLC, Boulder, Colorado, USA
5Cooperative Institute for Research in the Environmental Sciences, University of Colorado Boulder, Boulder, Colorado, USA
Abstract. Interannual variability of wind speeds presents a fundamental source of uncertainty in preconstruction energy estimates. Our analysis of one of the longest and geographically most widespread extant sets of instrumental wind-speed observations (62-year records from 60 stations in Canada) shows that deviations from mean resource levels persist over many decades, substantially increasing uncertainty. As a result of this persistence, the performance of each site's last 20 years diverges more widely than expected from the P50 level estimated from its first 42 years: half the sites have either fewer than 5 or more than 15 years exceeding the P50 estimate. In contrast to this 10-year-wide interquartile range, a 4-year-wide range (2.5 times narrower) was found for "control" records where statistical independence was enforced by randomly permuting each station's historical values. Similarly, for sites with capacity factor of 0.35 and interannual variability of 6  %, one would expect 9 years in 10 to fall in the range 0.32–0.38; we find the actual 90  % range to be 0.27–0.43, or three times wider. The previously un-quantified effect of serial correlations favors a shift in resource-assessment thinking from a climatology-focused approach to a persistence-focused approach: for this data set, no improvement in P50 error is gained by using records longer than 4–5 years, and use of records longer than 20 years actually degrades accuracy.

Citation: Bodini, N., Lundquist, J. K., Zardi, D., and Handschy, M.: Year-to-year correlation, record length, and overconfidence in wind resource assessment, Wind Energ. Sci., 1, 115-128, https://doi.org/10.5194/wes-1-115-2016, 2016.
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Short summary
Year-to-year variability of wind speeds limits the certainty of wind-plant preconstruction energy estimates ("resource assessments"). Using 62-year records from 60 stations across Canada we show that resource highs and lows persist for decades, which makes estimates 2–3 times less certain than if annual levels were uncorrelated. Comparing chronological data records with randomly permuted versions of the same data reveals this in an unambiguous and easy-to-understand way.
Year-to-year variability of wind speeds limits the certainty of wind-plant preconstruction...
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