Accurate wind resource assessments
reduce uncertainty in wind farm energy yield projections. This is
particularly important offshore where development costs are high. The
lack of hub height measurements of wind speed may require the
extrapolation of observed wind speeds from lower measurement heights.
The power law and logarithmic profile are the two most frequently
used techniques. As these methods assume neutral stability, the
application of an atmospheric stability correction term may lead to
significant improvements in the predictions of the Vertical Wind
Profile (VWP). The aim of this study is to find the most accurate
method of modelling the VWP in the marine environment. Influences
such as: (i) the required time resolution of data; (ii) temperature
measurements; (iii) measurement heights; (iv) the parameterisation of
sea surface roughness based on fetch type and (v) the necessary
measurement parameters to model the VWP are investigated. Analysis of
measurements from the Egmond aan Zee offshore wind farm and a site on
the east coast of Norway are presented. Uncertainty remains over the
most accurate method of calculating the Obukhov Length based on
standard 10 minute time averaged measurements. Monin-Obukhov theory
is valid in a limited range of conditions. To carry out a
comprehensive wind resource assessment, the use of the entire dataset
is desirable. Filtering the data to conform to M-O theory may lead to
a large reduction in the time series of measurements used.
Therefore, a trade-off must be made between temporal coverage of the
measurements and strict compliance with M-O theory.