An Independent Analysis of Bias Sources and Variability in Wind Plant Pre-Construction Energy Yield Estimation Methods

Austin Todd, Mike Optis, Nicola Bodini, Michael Fields, Jordan Perr-Sauer, Joseph Lee, Eric Simley, Robert Hammond

Research output: Contribution to journalArticlepeer-review


The wind resource assessment community has long had the goal of reducing the bias between wind plant pre-construction energy yield assessment (EYA) and the observed annual energy production (AEP). This comparison is typically made between the 50% probability of exceedance (P50) value of the EYA and the long-term corrected operational AEP (hereafter OA AEP) and is known as the P50 bias. The industry has critically lacked an independent analysis of bias investigated across multiple consultants to identify the greatest sources of uncertainty and variance in the EYA process and the best opportunities for uncertainty reduction. The present study addresses this gap by benchmarking consultant methodologies against each other and against operational data at a scale not seen before in industry collaborations. We consider data from 10 wind plants in North America and evaluate discrepancies between eight consultancies in the steps taken from estimates of gross to net energy. Consultants tend to overestimate the gross energy produced at the turbines and then compensate by further overestimating downstream losses, leading to a mean P50 bias near zero, still with significant variability among the individual wind plants. Within our data sample, we find that consultant estimates of all loss categories, except environmental losses, tend to reduce the project-to-project variability of the P50 bias. The disagreement between consultants, however, remains flat throughout the addition of losses. Finally, we find that differences in consultants' estimates of project performance can lead to differences up to $10/MWh in the levelized cost of energy for a wind plant.

Original languageAmerican English
Pages (from-to)1775-1790
Number of pages16
JournalWind Energy
Issue number10
StatePublished - 2022

Bibliographical note

Publisher Copyright:
© 2022 The Authors. Wind Energy published by John Wiley & Sons Ltd. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

NREL Publication Number

  • NREL/JA-5000-81032


  • annual energy production
  • benchmark
  • energy yield assessment
  • open-source code
  • operational analysis
  • P50 bias
  • pre-construction estimates
  • pre–post-construction reconciliation
  • wind energy


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