The development of offshore wind farms has grown as demand for renewable energy has increased and in European waters 3,230 offshore wind turbines have already been installed. Overall the environmental impact of renewable energy is expected to be overwhelmingly positive, via the reduction of greenhouse gas emissions and the reduction of climate change.

The model has shown that wind farms can alter the heights of tides

The model has shown that wind farms can alter the heights of tides

However to date there has been little evidence gathered of the local or regional impact from these installations so a new study from Plymouth Marine Laboratory (PML) scientists sought to fill these gaps.

The Laboratory has used mathematical models to predict the impacts of offshore wind farms in coastal seas. Most previous studies have only focused on small-scale domains, for example a single wind farm. This new study investigated the impacts at scales from one individual turbine to a large scale area of wind farms based on the seven existing Irish Sea wind farms with a total of 242 turbines.

The PML scientists found that although the effect of each individual turbine is small, cumulatively they can change the local flow of water, with the turbines creating more mixing of the water in the vicinity of the wind farm. This changes the layers of water which form around the wind farms, potentially altering the local ecosystems. As the majority of future offshore wind expansion in the UK happens to be focused in regions which the seas are seasonally stratified, this work was considered crucial in order to inform decision making on how those new developments are implemented, in order to best optimize their siting.

The model also showed that the wind farms can alter the heights of tides. These changes extend around the whole UK coastline and unlike previous models, which have restricted the domains investigated to the immediate area adjacent to the installations, this study expanded the domain and indeed found so-called far-field effects as far away as off the south-east coast of England.

This showed increases in a component of the tide of 1%-2% (about 6cm-12cm). Small changes like this could have consequences for coastal habitats. Also given the economic investment around parts of the UK coast, any potential change in tidal height may redistribute flooding risks. This study suggests a potential contributing factor to that increase in addition to factors such as increased storminess, climate change and changes in river discharge.

Given that the wind farms used in the model are relatively modest yet still demonstrate both local and far-field impacts, this research, the scientists say, will help to inform developers of future, potentially larger, offshore wind farms and the regulators who decide on the locations of the developments. It is also of interest to the insurance industry and the public at large due to changes in the tides and possible impacts on flood risk.

By Dag Pike