Analysing weather windows for offshore wind in Germany using combined meteorological and oceanographic reanalysis data

The goal is clear: by 2045, offshore wind energy in Germany should be increased substantially from ~9 GW today to nearly 70 GW, with offshore wind expected to provide up to 25 % of the national electricity demand. Achieving this target requires the development of offshore wind in increasingly remote areas from the shore, where observational data including suitable reference measurements are limited and the atmospheric and oceanographic conditions are less well understood. However, a critical factor for the safe and cost-effective installation, operation, and regular maintenance of the offshore wind farms is the identification of “weather windows” – periods when atmospheric and oceanographic conditions are below the operational limits of the vessels used. These weather windows influence the installation time and the accessibility during the operation of offshore wind turbines, as well as the requirements for the necessary vessels, and thus the financial viability of the offshore wind projects including the corresponding bid during the tendering process for an offshore wind site.

To achieve Germany’s offshore targets, new offshore wind sites are tendered annually since 2021 by the Federal Network Agency, in cooperation with the Federal Maritime and Hydrographic Agency (BSH), according to the Offshore Wind Energy Act (WindSeeG). The German Weather Service (DWD) supports the BSH in compiling detailed information on the prevailing meteorological conditions at the tendered sites and in continuously providing new and improved products. The meteorological dataset for each site typically consists of one year of in-situ measurements with a floating LiDAR and several long-term reanalysis datasets, where both provide the basis for the comprehensive report of an offshore wind site. All data and reports are publicly accessible via the BSH’s PINTA portal – https://pinta.bsh.de.

This study presents a new comprehensive assessment of combined wind and wave conditions for selected offshore wind sites, using multi-decadal atmospheric and oceanographic reanalysis data. The weather windows are calculated based on generic thresholds relevant to the offshore wind industry, with a focus on near-surface wind speed and sea state. The study shows the identification of patterns of favourable conditions considering both average and extreme cases. Furthermore, the analysis highlights differences in the distribution of weather windows between the various reanalysis datasets considered. This underlines the need for high-quality, site-specific in-situ measurements and thus the importance of the data that is provided year after year via the PINTA portal.