Future offshore wind projects off the Outer Cape, in the Gulf of Maine, are likely to use floating turbines anchored to the seafloor. That’s different from turbines currently being installed south of Martha’s Vineyard, which are atop foundations driven into the seabed. To learn more, CAI’s Jennette Barnes interviewed Javier Molinero, a civil engineer who specializes in floating wind technology at consulting company DNV, which has done work for the states of Massachusetts and Maine.
Jennette Barnes: My understanding is that the primary reason floating wind would be used off Maine is because the water is deeper than it is where Vineyard Wind is located. But it still has to be anchored to the bottom. So what are the reasons that floating wind is used? What are the advantages?
Javier Molinero: There's a couple of factors. It doesn't work the same way in all areas, of course, but the farther offshore you go, the wind resource is steadier and stronger. The floater itself is way more complex because it works more like a ship or a boat. That means a higher amount of steel or concrete to provide this buoyancy. Plus, the cables and all these ancillary components are more in a more dynamic configuration. And that's more complex and generally it’s more expensive. So, you see, I think the water depth is the main driver. Generally if you go farther offshore, the wind resource is better, so there is a little bit of a tendency to explore farther areas where you can only do floating configurations.
Jennette Barnes: Now I want to talk a little bit about the hardware. How are the anchors secured to the bottom if you're in these very deep waters, or relatively deeper than the fixed foundation system?
Javier Molinero: That's a great question. Actually, it’s one of the main points of complexity of floating offshore wind. So my answer is that it depends on the water depth. And it also depends on the type of anchor. These anchors basically have to be tailor-designed and engineered in order to work in certain environments. So, for example, depending on your load level, or on the type of soil that you have on the seabed, you're going to be choosing one type of anchor or another. There are some anchors that basically get embedded into the soil by providing a pulling force. So that's the most simple, cheapest way of deploying an anchor. On the other side of the spectrum, when you go to deep waters, when you think about, for example, the offshore wind areas in California, you're going to have to be thinking about a more sophisticated type of anchor, where you actually need to operate remote operated vehicles. And as you can imagine, this is a more complex and more expensive type of process.
Jennette Barnes: You've mentioned the cost and how it can be greater than with the fixed-bottom wind. Is that likely to result in a higher energy price for the power from floating wind?
Javier Molinero: It's more expensive for now, but if we're able to deploy larger offshore wind farms in floating configuration, then we're going to be able to scale up the design. We're going to be able to fabricate the floaters in a more efficient way, and we're going to be caring a little bit less about the geology of the site. So, we believe that in these economies of scale, in this process of industrialization, in the long shot, floating wind has advantages to actually put the levelized cost of energy, of floating wind, closer to fixed-bottom.
Jennette Barnes: I want to ask you a little bit about any challenges to wildlife or habitat from the floating turbines, the anchors, and especially the lines, because we know that, there have definitely been cases where wildlife have gotten tangled in lines. Is there potential for that if, you know, if there's slack in these lines?
Javier Molinero: There is a lot of processes in place in order to ensure that all the environmental impacts are minimized. We try to minimize the footprint, the locations that can be impacted by these technologies. These areas have been previously screened against, you know, marine mammals, migrations, marine traffic, sea impacts. Especially in Maine, there has been a lot of work done in the space of minimizing all these impacts for the fishing communities, which we understand are super important and key for the socioeconomic development of the region.
Jennette Barnes: Do you know what the lines will be made of in the Gulf of Maine? I mean, is it some kind of chain, or rope-like structure? What is it?
Javier Molinero: Yeah, so, in [the] Gulf of Maine, we are ranging between 100, 150, and 300 meters. You could easily just consider a catenary system. Catenary systems are simple. They are based on a heavier, lower segment in the lower part of the mooring line. And that will be counterbalancing any sort of lateral displacements of the floater in the upper, surface level. Normally in the lower part you go for chain sections. You can actually include some ancillary components that are called clumped weights in order to increase this weight in the lower part. And the upper part can be different rope, polyester, nylon components that are lighter and a little bit more flexible than the chain.
Jennette Barnes: Javier Molinero, leader of floating offshore wind for consulting firm DNV, I really appreciate you doing this.
Javier Molinero: I really appreciate your time, Jennette. Thank you very much for having me.
This interview has been edited for length and clarity.
