Offshore wind: It's more expensive than we thought

Trying to work out how close together you can pack turbines in an offshore windfarm is a vital engineering decision for the developers of offshore windfarms. That’s because the turbine wake – the slower and turbulent air that has just passed through the turbine can reduce the output of any downwind turbines.As turbines become bigger, their wakes become much larger, and so, over time, engineers have been advising larger and larger spacing (Figure 1).

But the engineering models are, well, models, and each time a new, larger generation of turbines is introduced, they enter terra incognita: a scenario that is outside the range of their calibration data.Inevitably, they sometimes get it expensively wrong. The Burbo Bank Extension windfarm is currently paying over 5% of its turnover to next door Burbo Bank Windfarm in compensation for wake losses.

Now, an important new working paper from renewables consultants ArcVera is reporting that wake effects behind the huge turbines that are now coming on stream are going to be much worse than previously thought. The conventional engineering wisdom is that there will be a 10—15% loss of output for a turbine placed less than 2 km downwind of another. ArcVera are suggesting that new windfarms could experience losses of as much as 25% at a distances of 10 km(!).

The paper is another model, so it too needs empirical validation, but if it’s right the implications are very serious for windfarms coming on stream. Turbines are going to have to be spaced much further apart, and windfarms are going to need to be further apart too. This is just going to increase the cost of an inherently expensive technology still further. And you are going to foot the bill.