The Cost of Shear Uncertainty in an Era of Higher Hub Heights

Wind turbine hub heights have increased substantially in recent years, with turbines that have hub heights exceeding 90 meters capturing almost 50% of US market share in 2018, up from just 20% in 2016. These higher hub heights, combined with data collection campaigns that often only deploy 60 meter met masts, lead to an increase in shear uncertainty. Given the strong diurnal and seasonal fluctuations in wind speed and power market price and the exposure of these prices on wind farms due to the lack of fixed price utility PPAs, it is important to consider the financial impact of this increased shear uncertainty.

This analysis examines the impact that different shearing methods have on hourly wind speed, energy and revenue error. Potential impacts will be quantified using geographically diverse measurements from tall met towers and remote sensing devices in combination with observed power prices. Observed wind speeds will be translated into production using a hypothetical wind plant power curve. Multiple shear methodologies will be compared including calculation of shear parameters using a 12x24 matrix and on a time series basis. Understanding the diurnal and seasonal impacts of shear uncertainty in the revenue space will assist the wind resource assessment community in determining optimal shearing methodologies. In addition, this analysis will demonstrate the value of including taller met towers and remote sensing instruments in pre-construction met campaigns.

Learning Objectives:

• It is important to consider the known diurnal and seasonal covariance of wind speed and power price when estimating shear uncertainty.
• Shearing parameters can vary significantly on a time-series basis when compared to averaged values from a 12x24 matrix.
• Even if bias and error are small for a particular shearing method in the wind domain, error and bias can still be significant in the revenue domain