Onshore vs Offshore Wind: Cost, Resource and Why Floating Matters

Onshore and offshore wind use the same physics and very different economics. The comparison comes down to a trade: offshore buys a better resource and pays for it in construction and maintenance.

The resource difference

Offshore wind is stronger and steadier.

There is no terrain to create friction and turbulence — no hills, buildings or trees. Airflow over open water is smoother and faster, and it varies less.

That shows up in the capacity factor: the proportion of theoretical maximum output actually achieved. Onshore wind typically achieves roughly 25 to 45 percent depending on site quality. Offshore commonly reaches 40 to 55 percent.

Because available power scales with the cube of wind speed, as we explain in how wind turbines work, that resource advantage is worth more than the percentage gap suggests.

Steadiness matters separately from strength. Output that varies less is easier to integrate, more predictable to forecast and more valuable to a grid operator.

Why offshore turbines are enormous

Onshore turbine size is limited by logistics rather than engineering. Blades must travel roads, negotiate bends and pass under bridges. Cranes must reach hub height and be transported to site.

At sea, components travel by vessel and are installed by purpose-built ships. Those constraints disappear, and turbine size has grown accordingly — offshore machines are now dramatically larger than anything practical on land.

Larger turbines matter because swept area scales with the square of blade length. Fewer, larger machines also mean fewer foundations, fewer connections and fewer maintenance visits — which, offshore, is a substantial saving.

Where the cost goes

Offshore capital cost is much higher, and it is worth knowing where:

• Foundations. Structures fixed to the seabed in tens of metres of water, engineered for waves, currents, corrosion and storms.
• Installation vessels. Specialised ships with limited global availability, chartered at high day rates.
• Subsea cabling. Array cables between turbines and an export cable to shore, all requiring burial and protection.
• Offshore substations, themselves sizeable marine structures.
• Weather delays. Installation windows depend on sea state, and waiting costs money.

The maintenance problem

This is where offshore economics differ most fundamentally, and it is frequently underestimated.

An onshore turbine fault means driving a technician to site. An offshore fault means a vessel or helicopter, favourable weather, trained personnel and specialised equipment. A fault occurring during a storm season may remain unrepaired for days or weeks while the asset produces nothing.

The consequences run through the whole design philosophy:

• Higher reliability requirements, because access is expensive.
• Condition monitoring and predictive maintenance are essential rather than optional.
• Marine corrosion protection throughout.
• Higher operating costs across the asset's life.
• Availability guarantees becoming central commercial terms.

Floating offshore wind

Conventional offshore turbines need foundations fixed to the seabed, which becomes impractical beyond roughly 60 metres of water depth.

That is a serious constraint. Many coastlines — including much of the Mediterranean, parts of Asia and the Pacific coasts — drop steeply, leaving little shallow shelf.

Floating foundations mount turbines on platforms moored to the seabed. Several designs compete: spar buoys, semi-submersibles and tension-leg platforms, each with different stability characteristics and installation requirements.

What floating changes:

• Deep water becomes accessible, vastly expanding viable sites.
• Turbines can be positioned further offshore, where wind is stronger and visual impact is negligible.
• Assembly can occur in port rather than at sea, potentially reducing installation cost and weather exposure.
• Damaged units can, in principle, be towed to port for major repair.

Floating wind remains at an earlier commercial stage with higher costs, but its trajectory is the one that determines whether offshore wind is available to countries without shallow continental shelves.

Relevance to our coverage regions

Offshore wind has been slower to develop across the Middle East and South Asia than in northern Europe, for identifiable reasons:

• Excellent and much cheaper solar sets a demanding cost benchmark, as we explain in why Gulf solar is so cheap.
• Available onshore land in much of the region, unlike densely populated northern European coasts.
• Water depth and seabed conditions varying considerably.
• Supply chain and installation vessel availability, concentrated in established markets.

India has pursued offshore wind assessment and tendering, and the economics will depend on grid value, resource measurement and supply chain development. Elsewhere, onshore wind and solar-plus-storage remain considerably cheaper routes to the same outcome.

How to compare them properly

Do not compare capital cost per megawatt. Compare levelised cost of energy, which accounts for the higher output offshore delivers across its life.

Then adjust for two further factors most comparisons omit:

• Grid value, since steadier, more predictable output is worth more than variable output.
• Land opportunity cost, which is high in dense regions and near zero in desert.

Those adjustments frequently change the answer.

The bottom line

Offshore wind buys a better resource at a higher price, and whether that trade makes sense depends on land availability, water depth and what a grid pays for steadier output. Floating foundations are the development that determines whether the option exists at all for steep coastlines.

Follow wind development across our regions

Wind's value rises as solar penetration grows, which makes it increasingly strategic across the Middle East and South Asia.

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