Characterization and forecasting of wind conditions over the Baltic Sea

Sammanfattning: To meet the increasing demand of sustainably produced electricity, the total number of installed wind turbines is rapidly increasing globally. Although onshore installations are dominating, offshore wind power is taking a greater share of the market every year. Offshore, the wind is generally stronger than onshore and with the possibility to construct bigger turbines the electricity yield is also greater per turbine. Furthermore, it is possible to build larger wind farms offshore than onshore. The Baltic Sea is an area of high interest to many stakeholders and a major expansion of offshore wind power is expected in the region in the coming decades.As the Baltic Sea is a semi-enclosed sea with relatively short distances to the coast from anywhere in the basin, there are many mesoscale meteorological phenomena occurring, affecting the shape of the wind profile and the preconditions for wind power. This thesis focuses on these wind profiles, utilizing multi-year lidar observations and state-of-the-art numerical models. Wind profiles with a local maximum, i.e., low-level jets, are of special interest as they are frequently occurring over the Baltic Sea. These non-ideal wind speed profiles are characterized in terms of frequency and effects on turbulent properties, and the best way to define the low-level jets is investigated. Furthermore, the change in wind direction with height is addressed and a new index to automatically identify sea and land breeze circulations in operational weather prediction models is created. Finally, different post-processing methods to improve short-term forecasts of wind power production are compared and a recommendation on how to combine the methods depending on the weather situation is presented. Altogether, the research in this thesis adds a piece to the puzzle in reaching further understanding of the Baltic Sea wind conditions. The findings will be useful also in other coastal areas in siting, farm layout, and load analysis as well as in creating improved power production forecasts for offshore wind turbines.