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Pangea SI Expert Q&A: Floating Offshore Wind Deep Dive

November 23, 2021
Benjamin Ringrose

30 years ago developers started the rise of the offshore wind market. More recently, however, the market has taken a more ambitious direction: putting turbines on floating platforms in the water. With this floating offshore wind market nearing commercial maturity, floating wind holds the potential to become one of the most important new renewable energy markets on the planet.

We spoke with a couple of our top floating offshore wind experts to get their in-depth analysis and opinions on some of the major questions in the industry. Dive into what they had to say below.

Floating Offshore Wind: 6 Key Questions, 10 Expert Answers

Q: What are the main challenges with floating wind?

Floating Systems and Facilities Engineer: There are several hurdles to jump, but the top challenges as I see are:

  • Project development costs are expected to reduce over the coming years as FOW volume grows, but it hasn’t happened yet. It will need “factory” style fabrication and the adoption of quayside integration of increasingly larger turbines.
  • Larger distances from the O&M port locations and harsher environments necessitate a different approach to fixed wind O&M. Infield floating “base camps” are an option but add cost. One solution is to “design out” maintenance requirements and use digital twin and IOT technologies for effective predictive maintenance. Robotics and drones are likely to perform a greater proportion of inspection and maintenance tasks, launched from UAVs (which will also reduce the risk to personnel).
  • Transmission costs for FOW developments will be greater than for existing power generation options since FOW farms will be further away from the consumer locations.
  • Larger size dynamic export cables for floating substations still need further development. One alternative is to use fixed platform substations where water depths permit, or multiple smaller dynamic cables to achieve the required export capacity.
  •  

    Offshore Renewable Energy Engineer: Floating wind is the latest evolution of wind energy, and there is only a handful of floating offshore wind farms with multiple units, the main ones being:

  • Hywind Scotland pilot park, operating since 2017, with 5 turbines of 6MW.
  • Windfloat Atlantic, with 4 wind turbines.
  • Kincardine Floating Offshore Wind Farm.
  •  

    Therefore, I would say the main challenge is a low maturity and little experience – but it is catching up quite fast.
    Technically, the harsher metocean conditions found in the deeper waters, further from shore sites suitable for floating wind makes the design and operation & maintenance more challenging.

    At a higher level, the industry is pushing for a convergence of designs to establish a supply chain able to deliver the hundred/thousands of units needed to fulfil the UK 1GW = 1000MW floating wind turbines target by 2030.

    Q: What makes floating wind better then onshore or fixed offshore wind farms?

    Offshore Renewable Energy Engineer: Floating wind is more economically viable for water depths exceeding, roughly speaking, 50m – and it is estimated that worldwide, a large percentage of the offshore wind resources are located in these water depths. Some countries, like Japan, west coast of the USA, are not as lucky as England in having a large shallow area, and floating wind will be one of the only technological offshore wind solutions available.

    In these sites, the wind velocity tends to be higher (the power goes with the cube of the wind speed!), and more consistent, leading already to record performance of the installed floating wind turbines: the Hywind Scotland Pilot Park has one of the highest capacity factors among all the offshore wind farms out there (fixed to the bottom and floating).

    Furthermore, floating wind turbines have the potential to be assembled quay-side, turbine and support structure, which would avoid the need for very expensive and scarcely available specialised installation vessels used for fixed wind turbines. Indeed, for fixed-to-seabed wind turbines, it is necessary first to install the support structure, i.e. the monopile “hammered” in the seabed, and then at a later stage install the wind turbine on top of the monopile. For floating, the wind turbine can be installed on the floating support structure quayside, and then used the floating support structure itself as a “transport vessel”, using relatively inexpensive and available ocean tugs (N.B. This is not true for some floating wind configurations, such as the Hywind SPAR).

    Q: How economically viable is floating offshore wind? How does its cost differ to regular fixed offshore wind?

    Floating Systems and Facilities Engineer: Today FOW is clearly more expensive than fixed wind and has not been developed on a commercial scale. Cost reductions in FOW are forecast to bring it in line with fixed wind. FOW may eventually achieve lower LCOE since the finite number of locations for fixed wind may limit further economies of scale.

    Offshore Renewable Energy Engineer: As every very young technology (the first operational floating wind farm is only 4 years old!), the levelised cost of energy is still higher than fixed offshore wind and onshore wind. On the other hand, the margins for improvement, for the same reason, are quite large, with a lot to be improved and learned – as explained in the report “FLOATING OFFSHORE WIND: COST REDUCTION PATHWAYS TO SUBSIDY FREE” by the Floating Wind Centre of Excellence, hosted by Offshore Renewable Energy Catapult.

    In the “Deliverable 2.8 Expected LCOE for floating wind turbines 10MW+ for 50m+ water depth” of the EU project Lifes50+ there is a nice graph comparing the levelised cost of energy for onshore VS offshore fixed VS offshore floating, showing how floating wind is expected to reach the same levelised cost of energy within the next decades.

    Q: With currently there only being a few active floating wind farms in the world, where do you think the floating wind industry will go over the next 5 years?

    Floating Systems and Facilities Engineer: The Venn diagram of opportunity overlaps for locations where:

  • Investors have confidence in achieving returns
  • There is a shortage of shallow water, preventing fixed wind
  • There is limited ability to access alternatives such as geothermal, hydro, or utility-scale solar power
  • That said, there is an immediate need to reduce the carbon footprint of offshore oil & gas platforms which currently use gas turbine power generation. The energy firms operating these facilities are also making big investments into renewables, including FOW. Nearly all have been studying how to replace the old gas turbines with FOW and other alternatives.

    Offshore Renewable Energy Engineer: The UK government alone has planned for 1GW (1000MW, and considering that an average MW per turbine from now until 2030 could be around 15MW, this would mean ~70 wind turbines) of floating offshore wind turbines by 2030, but countries like Japan and the USA, do need to go directly to floating with little bottom-fixed wind turbines. We will see, on one side, the industry converging on some standard designs (SPAR for deep waters, semisub for shallower waters), and on the other side the emergence of novel designs, such as the Tetraspar or Hexafloat, focusing more on ease of manufacturing.

    Q: What are the different models of floating wind platforms?

    Floating Systems and Facilities Engineer: There are more than 70 competing concepts, but they all fall into a few broad categories:

  • Semi-submersible
  • Tension leg platform (TLP)
  • Monohull / Barge
  • Spar
  •  

    There are a few variations, such as turret & swivel mooring as opposed to simple spread mooring.

    Offshore Renewable Energy Engineer: There are three main types:

  • SPAR, with a large draft, a low centre of gravity thanks to heavy ballast material at the bottom of the structure
  • Semisubmersibles, with a much shallower operational draft, but a large waterplane area, and therefore subject to larger wave loads
  • TLP, or tension leg platforms, in theory, are the most stable platforms (being the most rigid), but still without a large pilot or a demonstration floating wind farm to show its potential.
  • Working on the same stability principle as the semisubmersible, the barge by IDEOL exploit an internal moonpool to dampen the wave-induced motions, and in terms of other notable configurations, we must cite Tetraspar and Hexafloat, exploiting the same principle of the SPAR (i.e. low centre of gravity), but having in mind a mass-production design.

    Q: How will the growth of floating offshore wind bring about benefits to other sectors and businesses?

    Floating Systems and Facilities Engineer: This will represent a sizeable increase in infrastructure investment over the coming decades. It will alleviate the effects of the downturn in the offshore oil & gas sector which has opened up capacity that can be taken up by FOW. It will also create new growth in the supply chain and may challenge the resource base. There will be benefits across many more sectors. As capacity grows, so will the need for energy storage solutions. Availability of electricity will enable transition away from gas heating in homes, which in turn will spark the home heating sector into a new phase of activity.

     

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