No abstract

Offshore wind farms will become more frequent in the German part of the North Sea. High and continuous wind speeds, as well as remoteness to populated areas are advantages of offshore wind turbines. To evaluate the environmental sustainability and technical/financial feasibility of offshore wind farm expansion, the German Federal Government has decided to encourage the renewable offshore sector, among other things, with a comprehensive scientific research project (Research at Alpha Ventus (RAVE)) [1]. The RAVE project startet 2008 with first marine observations 2010. Purpose of this project is to enhance the sparely investigated knowledge of impacts of the harsh marine conditions with regard to construction and operation in offshore regions. Within this project, extensive oceanographic investigations are carried out.The measured oceanographic data is a basic dataset to the entire accompanying research, both for the technical aspects as for the environmental and geological investigations. Furthermore the influences of offshore structures and facilities should be examined with respect to shelf sea physics and vice versa. The present study shows results from five years of oceanographic measurements regarding to construction and operation of offshore wind farms. For that reason the focus is on sea state observations (installation, maintenance and data analysis) which have a major impact on the operational management of offshore facilities. In this paper, measurements with directional wave rider buoys, various radar level gauges (sea state parameters calculated from water level data) and ADCPs (with option to measure sea state) are compared and evaluated to their physical limits, ambient conditions, accuracies, as well as technical advantages and disadvantages. A better understanding of the instruments helps to optimize the measurement concepts in terms of type, number, measurement time and locations. In consequence this can lead to an improvement of offshore energy production facility design, robustness and dimensioning. Additional benefits can be an optimization of facility locations and access times during facility construction and maintenance, cost reduction as well as improved energy production rates.

In situ sea state measurements are essential for offshore activities, coastal protection and science (here in example for the validation of numerical models and of earthor satellite-based remote sensing instruments). Therefore, well quality checked data is a must. Up to now it is difficult to discriminate between outliers and extreme waves in raw surface wave displacement time series. A consequence of this fact is the uncertainty of the correctness of the maximum wave height in a time period and of extreme waves at all. A first approach method has been developed considering some physically motivated singlewave features. Aim of the development in progress is a fully automated procedure to ensure the sea state time series quality in regard of the discrimination of outliers and extreme waves; in consequence this could also increase the reliability of in situ extreme wave statistics.

<p>The Offshore Wind Energy Act (Windenergie-auf-See-Gesetz - WindSeeG) legally requires annual tender procedures for sites in the North Sea in the Exclusive Economic Zone of Germany for the construction of wind turbines. The Federal Maritime and Hydrographic Agency (Bundesamt für Seeschifffahrt und Hydrographie - BSH) conducts so called preliminary investigation of sites (PIS), pursuant to §10 WindSeeG. These include investigations of the wind conditions at the site, to give the interested firms information for calculating a bid. The preliminary investigation of the wind conditions is conducted together with the German Weather Service (Deutscher Wetterdienst) and is based on three elements: a measurement campaign at the site for one year, an evaluation of reanalysis data by the German Weather Service, and a report which brings together all available information about the wind conditions. These reports are published together with the measurement and model data and the results of all other preliminary investigations via the PIS-Data Hub https://pinta.bsh.de as part of the tendering process.</p><p>The sites that are dedicated for the construction of wind turbines are defined in the Site Development Plan (Flächenentwicklungsplan), together with the year of the intended tendering process. The first PIS have been successfully completed for two sites in the southeastern North Sea and for one site in the Baltic Sea in March 2021. In the years 2022 and 2023, a call for tender for sites N-3.5, N-3.6 and N-7.2 will be published. These sites are located in the southwestern part of the German Exclusive Economic Zone in the North Sea. At or near these sites, meteorological measurements have been conducted, using a floating lidar which was installed on a buoy (site N-7.2) as well as scanning lidars installed on the transition pieces of wind turbines (N-3.5, N-3.6). These measurements resulted in time series of vertical profiles of wind direction and speed, covering one year each, and giving information about the wind conditions at the sites at relevant heights of future wind turbines. In addition, temperature, relative humidity, air pressure, and sea surface temperature were measured.</p>

<p>Das Windenergie-auf-See-Gesetz (WindSeeG) schreibt vor, dass jährlich Windparkflächen in der Ausschließlichen Wirtschaftszone (AWZ) Deutschlands für die Bebauung mit Windenergieanlagen ausgeschrieben werden. Das Bundesamt für Seeschifffahrt und Hydrographie (BSH) führt auf diesen Flächen Voruntersuchungen zu den vorliegenden Umweltbedingungen durch. Diese umfassen unter anderem die Untersuchungen der Windverhältnisse auf der Fläche, um den Bietern Informationen für die Kalkulation ihres Gebots zu liefern. Die windbezogene Voruntersuchung erfolgt in enger Zusammenarbeit mit dem Deutschen Wetterdienst (DWD) und basiert auf drei wesentlichen Elementen: einer einjährigen in-situ Messkampagne, der Auswertung von Reanalysedaten durch den DWD und der Erstellung eines zusammenführenden Gesamtberichtes. Diese Berichte werden zusammen mit den meteorologischen Mess- und Modelldaten und den Ergebnissen der weiteren Voruntersuchungen auf dem Datenportal PINTA (https://pinta.bsh.de) als Teil der Ausschreibung veröffentlicht.</p> <p> </p> <p>Die zu bebauenden Flächen werden im Flächenentwicklungsplan zusammen mit dem Jahr der Ausschreibung festgelegt. In den Jahren 2022 und 2023 werden die drei Flächen N-3.5, N-3.6 und N-7.2 in der Nordsee ausgeschrieben. Die Flächen liegen im südwestlichen Teil der deutschen AWZ. Auf und in unmittelbarer Nähe dieser Flächen wurden meteorologische Messungen durchgeführt. Mit Hilfe einer Lidarboje (Fläche N-7.2) sowie mit Scanning Lidaren auf bestehenden Windenergieanlagen (für alle drei Flächen) wurden einjährige Zeitserien von Vertikalprofilen der Windgeschwindigkeit und -richtung erfasst, die Aufschluss über die Windverhältnisse in den relevanten Höhen der zukünftigen Windenergieanlagen geben. Zusätzlich wurden Temperatur, Feuchte, Luftdruck und Wasseroberflächentemperatur gemessen.</p>