Stand on the breakwater at Port Kembla on a clear morning and you can just about picture it: a line of turbines sitting out past the horizon, steady as the coal stacks behind you. What you can’t picture from the shoreline is the seabed underneath them, and that’s the bit that actually determines whether this country ever gets a working offshore wind farm. The fixed-bottom versus floating offshore wind question isn’t an engineering curiosity. It’s the whole ballgame for Australia’s offshore ambitions, because our continental shelf drops away fast almost everywhere that matters.
I’ve spent a fair bit of this year going back through developer feasibility studies and bathymetry charts for the declared zones, and the pattern is consistent. Where the water stays shallow for a long way out, fixed-bottom works and the economics are at least plausible. Where it doesn’t, floating is the only option, and floating is still, broadly speaking, a technology proving itself at commercial scale rather than one with a long operating record behind it.
What fixed-bottom actually means
Fixed-bottom turbines are bolted or driven into the seabed. Monopiles are the standard approach in shallower water, essentially a single steel cylinder several metres across hammered into the sediment, with the turbine tower rising straight off it. In deeper or more complex seabed conditions, developers use jacket foundations, lattice structures similar to oil and gas platforms, which spread the load across several legs.
This is the technology Europe has built its offshore industry on. The North Sea’s Hornsea projects, Denmark’s Horns Rev, the UK’s Dogger Bank, all fixed-bottom, all in water depths generally under 60 metres. It’s mature, it’s bankable, and contractors know exactly how to price it because they’ve done it hundreds of times. That maturity matters enormously when a developer is trying to get a final investment decision past a board or a superannuation fund’s investment committee.
The catch is depth. Past roughly 50 to 60 metres, monopile and jacket foundations get disproportionately expensive, the steel tonnage climbs fast, and at some point it simply stops making sense.
Where floating comes in
Floating turbines sit on a buoyant platform, tethered to the seabed with mooring lines and anchors rather than a rigid foundation. There are three broad platform families being commercialised: semi-submersible, spar-buoy, and tension-leg, each with different stability and fabrication trade-offs. None of them care how deep the water is, which is the entire point. You can float a turbine in 200 metres of water about as easily as in 80, within reason.
That matters here because Australia’s continental shelf is narrow and steep along most of the east coast. Go out a reasonable distance off Gippsland or the Illawarra and you’re often already past the depth where fixed-bottom foundations stop being economic. Europe had the North Sea’s broad, shallow shelf handed to it. We mostly don’t have the geographic gift, and that single fact shapes almost everything about how this industry will actually unfold here.
The cost gap is real, and it isn’t closing fast
Floating offshore wind remains meaningfully more expensive per megawatt than fixed-bottom, and anyone spruiking otherwise hasn’t read a recent cost-of-energy study. The mooring systems, the dynamic cabling that has to flex with a moving platform instead of sitting rigid, the port infrastructure needed to assemble and tow out a floating platform rather than install it piece by piece from a jack-up vessel: all of it adds up. Global floating capacity installed to date is measured in the hundreds of megawatts, mostly demonstration-scale projects in Scotland, Portugal and Norway. Commercial-scale floating arrays in the multi-gigawatt range exist on paper and in planning approvals far more than they exist in the water.
AEMO’s Integrated System Plan treats offshore wind, floating in particular, as a later-decade contributor rather than something firming the grid this side of 2030. That’s not pessimism on AEMO’s part, it’s a reasonably sober read of where the supply chain and the cost curve actually sit. I’d put it more bluntly than the ISP does: floating offshore wind in Australia is a 2030s story, not a 2020s one, and developers who imply otherwise in their investor decks are getting ahead of the engineering.
What this means for Australia’s declared zones
Run through the declared offshore wind zones and the depth story explains a lot of the strategic positioning. The Gippsland zone off Victoria’s coast has pockets of workable depth that have attracted the most serious fixed-bottom interest, which is part of why Victoria’s SEC revival and its offshore wind push has leaned so heavily on that particular patch of water. It’s also no accident that the state with the shallowest usable shelf is the one furthest along in approvals.
The Illawarra zone off the NSW coast tells the opposite story. When the Commonwealth shrank that zone significantly in 2024 to pull it further from shore and away from shipping lanes and sensitive visual corridors, it pushed much of the remaining area into deeper water, water that increasingly only makes sense for floating platforms. I wrote about that shrinkage at the time and the comment I keep coming back to is that the zone reduction didn’t just trim megawatt count, it changed which technology family the zone actually belongs to. Readers who want the detail on what was lost and why should have a look at the Illawarra offshore wind zone piece on BlueFloat’s status. The developer’s public modelling still shows plenty of turbines. The seabed contours tell you which of those turbines need a foundation that doesn’t exist yet at commercial scale in this country.
Further north, the Hunter zone sits somewhere in between, shallow enough in parts for fixed-bottom, deep enough further out that floating gets floated as the long-term answer. That ambiguity is doing a lot of work in developer marketing material that it probably shouldn’t.
Grid connection is still the harder problem
None of this foundation technology matters if the transmission isn’t there to take the power to shore. I’ve made this argument before and I’ll keep making it: turbine count is the easy number to put in a press release, connection capacity is the hard number that actually determines whether a project gets built. The comparison with onshore wind is instructive here, and I covered the grid-connection gap in detail in onshore versus offshore wind: the grid connection test. Offshore projects, whether fixed-bottom or floating, typically need purpose-built substations, either onshore or offshore, high-voltage export cables run for tens of kilometres, and a connection point on a grid that in places like the Illawarra and the Hunter is already carrying coal-fired generation that’s meant to exit this decade.
Floating projects add another layer of connection complexity because the export cable has to accommodate platform movement, which means dynamic cable technology that’s seen far less deployment than the static cables used on fixed-bottom projects. It’s a solvable engineering problem. It is not yet a cheap or a routine one.
The honest sequencing for Australia
If I had to bet on how this plays out, fixed-bottom gets Australia’s first commercial offshore wind farm into the water, probably off Gippsland, on the back of comparatively shallow water and a transmission corridor that’s already been the subject of serious planning work. Floating stays in the demonstration and early-commercial phase through the back half of this decade, with genuine utility-scale floating arrays a 2030s proposition at the earliest, contingent on cost curves that are currently moving in the right direction but not quickly.
That’s a more conservative sequencing than some of the zone-level announcements imply, and it’s worth saying plainly: I think a few developers are letting floating-platform ambition get ahead of what the supply chain and the cost base can currently support. The render always shows the full build-out. The planning overlay, the water depth chart and the current state of the global floating supply chain tell a slower story.
None of that means offshore wind is a dead letter for Australia. It means the industry here will likely look more like a staged build than the single dramatic gigawatt announcement the press releases prefer. Fixed-bottom first, in the patches of shelf shallow enough to support it economically. Floating later, once mooring systems, dynamic cabling and specialised vessels have had another decade of global deployment to bring the cost down. For context on how that compares with the onshore alternative that’s actually been built at scale here, it’s worth reading back through onshore versus offshore wind: which one gets built first, because onshore’s head start isn’t just about approvals, it’s about not needing a foundation technology that barely exists yet.
Worth keeping an eye on the AEMO Integrated System Plan’s next update and the Clean Energy Regulator’s project tracking for how these timelines shift. The water off our coast isn’t going to get any shallower. The technology has to catch up to the geography we’ve actually got, not the geography the renders assume.
– Callum Hayes, Wind & Offshore Correspondent