Espen Åkervik: Challenges in wind resource assessment

The wind power industry has grown mature over the last years. As an example wind power was the single branch within the energy sector that installed the most energy in Europe last year. With the EU 2020 goal it is estimated that within 2020 as much as 35 percent of its renewable energy will come from wind energy. In Norway a total of 430MW of wind energy is presently installed, delivering one percent of the total electricity production in 2009. However 2100MW more has been given concession. Wind resource assessment deals with the subject of determining the properties of the wind climate prior to building a wind farm. The most important parameters are the annual mean wind speed, the velocity and the directional distribution and the turbulence intensity. The standard method of achieving this information is by on-site measurements. However it is only possible to measure the wind climate at a few locations within the wind farm area. Therefore it is necessary to use local flow models (e.g. CFD) to evaluate the spatial variation of the wind climate within a wind farm area. In addition meso-scale meteorological models are applied to assess the regional wind climate at scales of 1km and larger. These models are capable of matching the measured data very well. Data from meso-scale models may be used as input to local flow models when measurements are not available. Once the local wind climate is obtained the wind turbines are placed optimally in the area and a production analysis is performed. This production analysis takes into account the wind climate, the power curve of the selected wind turbine type and the wake losses induced by the interaction of the turbines. With the increasing sizes of the wind farms in the years to come it becomes increasingly important to obtain more and more accurate description of both the local wind climate and the wake effects from the wind turbines. This renders it essential to improve both measurement techniques and the flow models. In addition many large wind farms are planned offshore, leading to the need of understanding the interaction of water waves and the wind profile.