Sea state measurements in germanys first offshore wind farm "alpha ventus" in the south-eastern part of the north sea

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.

Storm Franz: Societal and energy impacts in northwest Europe on 11–12 January 2007

“…Lightning strike rates have emerged as a particular problem for offshore wind turbines in their exposed setting, but Becerra et al (2018) highlight that actual strike rates on wind turbines are several times higher than theoretical predictions. Some evidence indicates that the North Sea during winter storms can yield extreme waves with the capacity to damage offshore wind infrastructure, as demonstrated by wave strikes on the FINO1 offshore meteorological tower during storms on 2006, 2009(Neumann and Nolopp, 2007Outzen et al, 2008;Fischer et al, 2010;Pleskachevsky et al, 2012;FINO1, 2014). In particular, the wave strike on 1 November 2006 caused damage up to a level just below the main deck at 20 m above sea level, and high frequency water level recordings appear to reveal one of the largest waves ever documented in the region (Pleskachevsky et al, 2012).…”

Derivation of Met-Ocean Conditions for the Simulation of Floating Wind Turbines: a European case study

“…At the same time however, realistic environmental conditions could help to improve future FOWT designs, helping researchers to overcome potential issues of turbine upscaling, as highlighted in [6]. For researchers looking into analyzing marine structures installed in relatively shallow waters, such as fixed-bottom offshore wind turbines, the FINO monitoring platforms [7,8] provide an exceptional high-quality public dataset. For researcher focusing on deep-water installations such as in Floating Offshore Wind Turbines (FOWTs) however, this dataset is affected by the interaction of the waves with the seabed, causing changes to the ocean parameters that are not representative of deep-water sites.…”

Storm Anatol over Europe in December 1999: impacts on societal and energy infrastructure

“…It attempted to characterize the maximum size, location, and encounter probability of rogue waves using different approaches that included databases of ship accident reports (Toffoli et al, 2003) and synthetic aperture radar images (Lehner et al, 2002;Lehner, 2004). Rogue waves became an issue for offshore wind energy later in the first decade of the 21st century with wave strike damage on the FINO1 offshore meteorological mast in the German Bight during severe winter storms in , 2007(Neumann and Nolopp, 2007Outzen et al, 2008;Fischer et al, 2010;Pleskachevsky et al, 2012;FINO1, 2014).…”