Sea-based wind energy provides a substantial contribution to a durable energy supply for the Netherlands. But this durable energy should not come at the expense of the wealth in biodiversity of our North Sea. As such, windfarms must be installed and managed with respect for the natural world. This calls for up-to-date, reliable, and complete data, for example on bird and bat migration events and behaviours. Commissioned by the Ministry for Economic Affairs and Climate, Rijkswaterstaat has installed sensors in and around windfarms. The data gathered by these sensors is then offered to various different users for various different purposes.
Towards a model for sea-based bird migration
Sadly, accidents involving birds and rotating windmill blades are a regular occurrence. The solution seems simple: stop the blades as soon as a large group of birds appears. But stopping the blades is never an instant decision: to make sure that they can guarantee a continued supply of energy even when the wind turbines are stopped, the windfarm owners and the power grid operator have to take measures 48 hours in advance. In other words, we need to be able to predict bird migration events at sea 48 hours in advance. To that end, Rijkswaterstaat has asked the University of Amsterdam to develop a model that can be used to make these predictions.
From rough data to suprising insights
Special bird radar installations at and around the windfarms provide the data needed to model migration behaviours. These are the same radar installations as those used on sea-faring vessels, but with a different system integration. Robin Radar software interprets the radar data even as it is gathered at sea. This means we do not have to send the rough data to shore first. The software classifies moving objects based on their speed and mass. The different categories include aircraft, f locks of birds, and small, medium, or large birds. Every ten minutes, the system sends a copy of the data to the Rijkswaterstaat computer centre, from where it is forwarded to interested users. The first research results have already been obtained, leading to some surprising insights: compared to previous assumptions, birds have been shown to cruise at wind blade altitude more often during the autumn.
There is more life in and above the North Sea
In addition to bird radar installations, we have also installed bat detector microphones. These pick up and record the high-frequency sounds made by bats. The microphones provide us with a better insight into the presence and species of bats around the windfarms - bats like Nathusius’s pipistrelle (Pipistrellus nathusii) and the common noctule (Nyctalus noctula) regularly frequent the North Sea. We also use ecology sensors to chart what happens below the surface of the water. This includes studies into the effects of underwater noise on harbour porpoises and seals, and on the influence of the electromagnetic fields around the cables below the windfarms.