A swarm of bats flies towards a wind farm. The DT bat system of the wind turbines detects the bats and calculates whether it is necessary to stop the wind turbines to avoid collisions. We don't want collisions of bats, of course, but we also want as little yield loss as possible. For example, to optimize the DT bat system each time, our wind specialists make calculations to find the best ratios. Our wind specialist Jorn Goldenbeld explains how much impact calculations can have and when they are needed.
Calculating whether a calculation is needed
'Every possible loss at wind farms can be calculated. Think of the impact of rainfall, the season, flocks of birds, maximum noise, maximum cast shadow on houses and so on,' Jorn explains. 'But making calculations of course also costs money. So, sometimes it is better to postpone certain calculations until later in the project or even take the small loss for granted because a calculation can be very time-intensive. Through knowledge and experience, we know when which research has enough impact on projects.' So, in the case of small losses, sometimes the choice is made not to investigate further how a yield loss can be reduced. But in the case of Windpark Zeewolde, for example, which has 91 wind turbines, a small loss of 0.14% can already have significant consequences and cause millions in losses.
Bats also fly at Wind Farm Zeewolde. To minimize the impact on these swarms, a mitigation algorithm that was established in 2018 was held on to.
During the construction phase of the wind farm, the province received an ecological study with new metrics that would reduce the loss calculation. The project team, without a wind specialist, examined the new possibility and concluded that production losses would be reduced by the new algorithm. The new algorithm had a few advantages: it would no longer have to be implemented on the entire bat period, could be applied to fewer turbines in total, could be grouped into a spring algorithm and a fall algorithm, and the daily period was reduced by 3 hours.
After implementation, the production loss only went from 0.14 percent to 0.22 percent. This small difference of 0.08 percent unfortunately resulted in millions of additional losses.
The impact of small percentages
At this point, our Solution Team was called in. 'We quickly realized that with the new algorithm several other things changed. For example, the approach wind speed threshold went from 5 m/s to 5.5 m/s and the temperature threshold was lowered from 12 to 10 degrees,' Jorn explains. Green Trust then created seven scenarios with different combinations of the parameters to show the county the impact of each individual parameter.
Jorn further explains the technical part: "This was an interesting exercise that showed that the impact of the lower temperature leads to a 0.01% increase in production loss, the increased run-up wind speed leads to a 0.09% increase in production loss, and the shortening of the period (a combination of hours per day and days per year) resulted in a 57% reduction in time, but "only" 0.02% reduction in production loss. In the end, we found a win-win situation where production loss was reduced 0.01% and the bats are even better protected! We hadn't had to determine a new algorithm before, so this was incredibly educational for us. And on such a large project it has a tremendous impact in terms of cost. I think it’s beautiful how much influence you can have on such a project as a wind expert. Next time we hope to get involved even earlier to save even more costs.'