Wind Catching Systems: Offshore Modular Multirotor Technology

Rosemary interviews Ivar Knutsen, Senior VP of Technical and Supply
Chain at Wind Catching Systems, to discuss their innovative
floating offshore wind concept. Wind Catching's design features a
grid of small wind turbines that benefit from the multirotor effect
and enable easier installation and maintenance compared to
traditional large offshore turbines. Wind Catching will also
present at the Multi Rotor 2024 seminar June 12-13. You can find
more information here: https://multirotor24.zohobackstage.eu/MR24.
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Rosemary Barnes: Welcome to a special episode of the Uptime Wind
Energy Podcast. I'm your host, Rosie Barnes, and I have today with
me Ivar Knutsen who is the Senior Vice President for Technical and
Supply Chain at Wind Catching. Thanks for joining us, Ivar. Ivar
Knutsen: Thank you for inviting us, Rosie. Rosemary Barnes: Okay,
so for those who don't know, I'm just gonna quickly start by
summarizing what the concept of Wind Catching is. So basically it's
a grid of wind turbines that is floating offshore. So you've got a
whole lot of small wind turbine turbines arranged in the grid, and
they're benefiting from being close to together with the multirotor
effect, which we'll get into later. And obviously there's also,
more modularity all the. Turbines are arranged in this grid so that
they can all yaw at the same time to face a differing wind
direction. And yeah I'll hand it over to you Eva to explain more
about what the concept is and yeah, why you decided that this was
a, an interesting company to get involved with. Ivar Knutsen: It
has become apparent to us that there are fundamental differences
Between a bottom fixed and a floating wind turbine and they those
differences are so big that you might need to Take a second look at
that, you need to maybe consider a completely new approach to the
design, but also to the operation. So we find that multi rotors
have three or four key benefits. One is that you're actually able
to avoid. The infamous tow to port. If the turbines are
sufficiently small, you can handle them offshore and perform a
turbine replacement offshore without using a crane vessel. You just
need to bring people aboard a unit as long as you have the right
technology to, to do that. And as, as we see it, there are no
options for. Return to port for big single rotor floaters today,
there are many concepts out there, but we don't see any of them as
being tackling the real problems is that it's going on in an
offshore environment with a lot of motions. The other thing we also
find very interesting about multirotors is that you decouple the
turbine development from the sort of the development, both on the
supply chain, but also on capacity. So if you can go from 20 to 30
to 40 megawatts without developing new turbines for every single
step, that's interesting. If you can use the same turbine, But you
can change your installed capacity by building on your support
structure. That is a very interesting part of the multirotor
concept. And the other thing is that with a standardized turbine,
you can actually enable a much broader supply chain. You can enable
local content in each country because the sophistication required
to turbine is much lower. And the reason for that, this is that if
you now look at the biggest turbines and the turbines expected to
come later. With blade lengths of 120, 130 meters to overcome the
scaling effect where the weight of those blades should scale
cubically with the length. They actually scale by the square and
that is done by introducing more and more sophisticated technology
in the blade design and manufacturing, which is really important.
Prohibitive to local content. You can't build those plates just
anywhere. Rosemary Barnes: Let's cover though what you said about
the modularity and the supply chain. So I think that's really
interesting. I think that's something that most people are aware of
that, modular technologies tend to reduce their cost faster. If you
look at the difference between solar panels and wind turbines,
that's a big difference is that the solar panels are a lot more
modular and they're yeah, can make the exact same thing many more
times, which tends to lead to, yeah, getting better at
manufacturing that thing and, making it cheaper. Then there's other
physical thing that you mentioned about how the structural scaling
laws, the amount of wind that you capture it scales with the square
of the length of the blade, but the volume scales with the cube. So
you actually. Don't get a better structural outcome from having a
big, one big rotor. You have a better structural outcome, like a,
less material should be able to be used if you have a lot of small
rotors than one equivalent large one. Yeah, so maybe you can talk a
little bit more about that benefit that you expect to get from the
modularity and the supply chain. Ivar Knutsen: What we're working
on now is a 40 rotor unit. So a 40 rotor floater which we see as
perhaps the lower scale or at least the lower region of what we see
as a fully commercial, not the pilot size, but they fully
commercial size. And I say for three rotors and the turbine we are
designing is a one megawatt, 30 meter diameter turbine. So 40
rotors is 40 turbines 40 megawatt. Having said that we have. That
kind of scalability on the turbine rating, we wouldn't probably
wouldn't differ in turbine diameter in rotor diameter, because that
has implications on the, how the design of the structure, not only
the, how you scale the structure, but the whole sort of arrangement
of the structure. But of course, turbine rating is something you
can play with on project specific basis, because we do see project.
Different types of projects, different types of markets. Even if
you start looking at electrification projects, where what we see,
interestingly, when I say electrification electrification of oil
and gas platforms, which is, has been done in Norway for some time,
and it's probably coming to Scotland as well. They are often very
clear and they have a clear cap on what they can receive of power
because their facilities can't receive any above, any sort of
access power can't be Received or utilized. Rosemary Barnes: So
yeah, you mentioned a couple of terms there that not everyone might
be familiar with. So you mentioned that there the rating is higher.
Ivar Knutsen: So meaning basically we have a higher rated wind
speed and a bigger generator relative to the rotor size. Rosemary
Barnes: Yeah. And it's usually an economic optimization to figure
out what that size should be. And you've come up with a different
answer than. Than others. Is that what you're saying? Ivar Knutsen:
Absolutely. And and it's an interesting question because you're
coming back to why our turbines like they are today. And that's not
a straightforward question to answer, because there's so many,
there's an evolutionary history that has led them in a certain
direction. But if you consider very large offshore turbines today,
we see that the rated wind speed has gone down. typically gone down
to now. If you see turbines 10 years ago, they were maybe had
ratings of 12 meters per second. And now we're see down to 10. 5.
You could get immense capacity factors by just reducing it down to
say rating at a five meter per second. And you would get like a
very good capacity factor, but it doesn't make sense. Rosemary
Barnes: You wouldn't get a lot of annual energy production though.
Ivar Knutsen: Yeah. So what I would say is that for very large
rotors what I believe is that the cost of generator size, so
increasing a generator size by 5 percent for a 15 megawatt turbine
is, has immense consequences. First off, you actually have to build
this, but you have to install it and you have to transmit the rotor
loads through this. And this comes from the same kind of scaling
law, but that applies to us as well. It just applies in the other
direction. So we have a very, a much, much lower impact on that. So
we could increase our generator size or decrease our generator size
by 20%. And it wouldn't really matter too much. Rosemary Barnes:
Because it's still a very small generator compared to what we're
used to handling. Ivar Knutsen: Yeah. So you're saving three tons
of generator weight per turbine, maybe if you make a substantial
change. And as long as you can handle the turbine well. Why not
just make a big generator? And that's what we're doing. Rosemary
Barnes: Yeah. Okay. That's really interesting. And I'm sure that
there are, a thousand different little tiny things like that, that
are different for your design than a regular configuration. But I
just want to go back to one other technical point that you
mentioned that people might not be familiar with. You said one P
and three P that's a tower passing frequency, right? Which I guess
when you've got a single. tower with a, a three bladed rotor on it,
then that's obvious what that means every time that the yeah,
there's a certain frequency of when the blades are passing the
tower. Your design has this big grid latticework there's not just
one tower and three blades anymore, there's What have you got, 120
blades if you've got three blades per rotor and all sorts of
components of a tower latticework. That's opening a huge can of
worms structurally, right? Because I know that,