Explained — Technology · 01.1
Wind Turbines
TurbineA rotary mechanical device that extracts energy from a fluid flow · The machine that converts moving air into usable electricity.
A modern offshore wind turbine is a 15 megawatt machine the height of a 60-storey building, designed to run for 25 to 30 years in salt spray, 100 mph winds, and minimal crew access. It is a structural, mechanical, electrical, and software problem solved simultaneously, and the fact that anyone makes a commercial return on one is a minor miracle of engineering discipline.
The physical scale does most of the commercial work. Swept area grows with the square of rotor diameter, so doubling blade length quadruples the air the machine captures. That is why the industry has pushed from 3 MW turbines in 2010 to 15 MW today, and why 18-20 MW machines are already in certification. Bigger turbines mean fewer turbines per farm, which in turn means fewer foundations, shorter cable routes, and fewer service vessel movements. The economics of everything downstream follow the turbine size.
The Modern Offshore Turbine
The current commercial standard is the 14 to 15 MW class, represented by the Vestas V236-15.0 MW, the Siemens Gamesa SG 14-236 DD, and the GE Haliade-X at 14 MW. Chinese OEMs have pushed further, with Mingyang's MySE 18.X-20 MW platform and Goldwind's equivalents targeting the domestic and emerging export markets. Western supply chain constraints and grid code certification cycles have kept 15 MW as the practical European default for projects reaching FID through the mid-2020s.
The Rotor
Three blades are still the norm offshore, for aerodynamic efficiency, structural load balance, and visual acceptance reasons that have held since the 1980s. Each blade is a composite structure, glass fibre reinforced polymer with carbon fibre in the spar cap, built in huge moulds at a handful of specialist factories. Blade design is the most closely guarded part of an OEM's intellectual property because small aerodynamic gains translate directly into energy yield over a 25 year operating life.
Blade pitch is actively controlled. Each blade has an independent pitch motor that rotates it around its own long axis, allowing the turbine to spill load in high winds, feather the blades when shut down, and shape the load profile across a single rotation. Individual pitch control (IPC) is increasingly standard, letting the controller compensate for wind shear and tower shadow on each blade independently.
Nacelle and Drivetrain
The nacelle houses the drivetrain, the generator, the converter, and the yaw and pitch control systems. Two main drivetrain philosophies dominate the offshore market.
Direct Drive (PMSG)
The rotor hub connects straight to a Permanent Magnet Synchronous Generator with no gearbox. Higher nacelle mass and bigger generator diameter, but no gearbox to fail and fewer wearing components. Favoured by Siemens Gamesa and GE.
Trade-off: higher up-front mass and rare-earth magnet cost, offset by simpler O&M and higher availability.
Medium-Speed Geared
A two or three stage gearbox runs a smaller, higher-speed PMSG. Lower nacelle mass and smaller generator, but an extra failure-prone component in the drivetrain. Favoured by Vestas.
Trade-off: lighter, cheaper to build, but gearbox reliability has historically been the single largest unplanned-downtime risk on offshore turbines.
Both architectures sit behind a full-scale power converter, which decouples rotor speed from grid frequency. This is the key feature of every modern variable-speed turbine. The generator spins at whatever speed the wind and controller dictate, the converter rectifies the AC output to DC, then inverts it back to grid-synchronised AC. This enables maximum power point tracking across the operating wind range, and it is also what allows the turbine to provide synthetic inertia, fast frequency response, reactive power support, and fault ride-through, all of which grid codes now require.
The Tower
Towers are rolled steel tubular sections, typically three to five sections bolted together, narrowing in diameter with height. Base diameter for a 15 MW machine sits around 8 to 9 metres. Material and fabrication cost have pushed some developers toward hybrid concrete-steel designs onshore, but offshore remains predominantly all-steel because of transport, installation, and corrosion protection logistics. The transition piece at the base, where the tower meets the foundation, is engineered separately and is covered in the Foundations page.
Control and Grid Services
A turbine controller manages pitch, torque, yaw, and converter settings on millisecond timescales. Above the individual machine sits a park controller that coordinates all turbines in the farm to meet a grid-side dispatch instruction, including active power curtailment, reactive power exchange with the grid, and voltage or frequency support. A modern offshore farm can deliver most of the services a conventional power station does, at higher response speeds than a thermal unit, provided the wind is blowing.
Availability figures quoted in marketing material (97 to 98 percent) usually refer to time-based availability excluding scheduled maintenance, grid curtailment, and environmental constraints. Actual energy-based availability is a more meaningful number, and is typically 2 to 4 points lower. Ask for it in kWh terms before signing anything.
The OEM Landscape
The Western offshore turbine market is effectively three suppliers: Vestas, Siemens Gamesa, and GE Vernova. Each has faced serious profitability and reliability problems over the last five years, with Siemens Gamesa's 4.X and 5.X onshore platforms requiring a multi-billion euro warranty write-down and GE pulling back from some European offshore commitments. The Chinese OEMs, Mingyang, Goldwind, Envision, and MingYang's newer platforms, are scaling aggressively domestically but remain effectively shut out of Western European markets by policy, financing, and grid code barriers.
For any project developer, the turbine supply agreement (TSA) is typically the single largest capex line item and the single largest source of schedule and performance risk. The commercial terms around serial defect liability, availability warranties, and power curve guarantees matter more than the marketed rated capacity.
Where This Goes Next
The 18 to 20 MW class is being certified now. Beyond that, scaling is genuinely constrained. Blade transport by ship is already at the practical limit of what ports and lay-up areas can handle, towers are approaching the limits of steel plate rolling diameter, and the installation vessel fleet is still catching up with current crane heights. Further gains are more likely to come from site-specific design optimisation, higher-specific-power rotors, and digital controls than from pure megawatt scaling.