New method to know where it is best to locate offshore wind turbines

Scientists have developed a mathematical-statistical method that allows us to know the degree of convenience of installing floating wind farms in a specific location. For example, whether or not there is a high probability that wind turbines will suffer mechanical fatigue or extreme marine conditions and that this will not be sufficiently compensated by the amount of energy harvestable at that location.

The work has been carried out by the EOLO research group of the University of the Basque Country/Euskal Herriko Unibertsitatea (UPV/EHU).

Alain Ulazia, professor at the School of Engineering of Gipuzkoa (Eibar), and his colleagues have used wind and wave data from a very energetic site on the coast of Ireland between 1920 and 2010 to analyze the evolution of sea conditions and generate a calculation model for the mechanical fatigue that these conditions can cause in floating wind turbines. This mathematical-statistical method allows calculating the life time of the turbines based on the meteorology of a specific location.

The most frequently asked question in offshore wind energy generation is usually “What changes (ups or downs) will occur in energy production depending on climatic conditions?”; That is, what is looked at is how much energy can be produced depending on the weather. However, the research led by Ulazia has gone a step further and has focused on the mechanical fatigue of offshore wind turbines, that is, the ultimate breakage as a result of repetitive shocks and stresses that are not capable of break the material individually: “Sea conditions (wind and waves) can influence the reduction of the life time of floating turbines. In fact, it is possible that they affect the life of some turbine parts more than the industrial production of energy, and instead of lasting 20 years they last 15 years. This can decisively influence the costs and investment of a project.”

The EOLO research group has been working on projects related to meteorology, climate and the environment for years. “We have carried out numerous studies on the long-term relationship between climate change and the generation of renewable energy. Taking into account the changes that have occurred over several decades, we carry out historical studies and projections for the future,” explains Ulazia.

Offshore wind turbines. (Photo: Dennis Schroeder / US National Renewable Energy Lab)

In this study, a very energetic place in Ireland has been selected: based on wind and wave data recorded between 1920 and 2010 in Galway Bay, on the west coast of Ireland, researchers have determined the historical changes that have occurred throughout those decades through the use of advanced meteorological models, in collaboration with members of the Ocean Energy Research Center at Maynooth University (Ireland). These historical data have been used to determine the evolution of marine conditions and create a model that represents the long-term fatigue that these will cause in the wind turbines. This model can be used to make future forecasts.

Using simulations, the researchers have calculated the energy that some reference floating turbines would produce in the eight most probable marine situations in Galway Bay and, on the other hand, they have seen the mechanical fatigue that they would cause in some elements of the turbines. “We have used a simulator that offers us in a few seconds the ‘dance’ that the turbine does due to the waves and the wind, and we have developed a mathematical-statistical method to implement changes in long-term marine states and, consequently, being able to determine the evolution of the fatigue that the machine would endure, taking into account these historical changes,” explains the researcher from the EOLO group.

Although the method has been applied in that Irish location, “this method is universal. We can do the analysis anywhere in the world,” she noted. Offshore wind energy is very appropriate because “it is not turbulent, like that of the mountains. However, much more must be invested in the sea. This is the main problem for the implementation of offshore wind energy,” explains Ulazia. Climate change is increasingly causing extreme events, and investors are cautious about the risk of this type of project: “Even if the site is very energetic, is it worth putting the wind farm there if at some point it can be seen?” affected by a weather phenomenon or if the turbine elements are going to suffer serious fatigue problems? The method developed by the EOLO research group of the University of the Basque Country allows us to have elements of judgment with which to answer this question in each specific case.

The study is titled “Historical trends of floating wind turbine fatigue loads (Ireland 1920–2010)”. And it has been published in the academic journal Ocean Engineering. (Source: UPV/EHU)