Floating wind farms and spring blooms

We have our Friday lunchtime similar series, and sometimes the speaker is internal. This week, that was the case. One of our researchers was taking the stage, talking about floating windfarms. I was glad I could make it, because the topic sounded fascinating. The particular thing about wind farms he was interested in was the turbulence they cause. If a current hits an obstacle like a wind turbine, turbulence is created in its wake. And turbulence matters for various reasons.

One thing this turbulence does is move sediment around. This can matter for creatures that don't like sediment falling on top of them. But it does more.

I suppose everyone reading this blog will have at some point seen satellite image of a plankton bloom. Plankton blooms tends to occur when in spring a water column becomes stratified. If you have relatively shallow water, then waves and tides will mix the entire water column through the winter. That means that both nutrients and those trying to eat them get churned around. Whatever wants to eat the nutrients needs sunlight to do so, so they can only function properly if they stay near there surface, where daylight penetrates.

In spring, the energy from the sun becomes strong enough to make the surface water so warm it becomes buoyant enough to not get mixed down anymore. And that means the nutrients that happened to end up in the surface water are now sitting ducks for the phytoplankton that wants to eat them. And these algae (other phytoplankton is available) don't have to worry about being removed from the surface water. So they have a veritable feast! And that basically is a plankton bloom.

The thing with the wind farms now is that it increases turbulence. And Ben, our speaker, had been worried about that added turbulence preventing the stratification that is needed for these spring blooms. That would be quite something!

He had been involved in projects where they took a little boat and sailed transects through the wake of monopile wind turbines. But of course that was a rather small scale endeavor! And your measurements will inevitably be taken while the tides are changing, so that makes the data difficult to interpret. Clearly, more of this kind of work needs to be done before they have a chance of quantifying this effect. 

He also said that plankton blooms have no legal rights. That didn't surprise me at all. What did surprise me is that what causes them, namely tidal fronts, do. If you build a wind farm in a location where tidal fronts occur you seem to have to justify that!

There is another side to this, of course. What if you build wind farms in the water that is so deep it doesn't normally mix all the way down? The increased turbulence might actually help productivity, by bringing nutrients into the surface water. And that is where the floating windfarms come in. These have been especially invented in order to be able to use these deeper waters. But the technology is still in its infancy!

With global warming, there is even the risk that more water will be stratified, just because the surface layers are so warm. If you can mix some of that heat down with a floating wind farm, you might be doing the climate of favour.

Offshore wind farms are in my thoughts quite often, but I must admit I had never really thought about their effect on turbulence, and what the implications thereof are! This was a really fascinating talk, and I am sure we will hear more about this topic in the future…

A wind farm seen from space; you can spot some turbulent trails behind the turbines. Pic by NASA.