Offshore wind is electricity generated by wind turbines built in bodies of water, usually the ocean. These turbines capture stronger, steadier winds than their land-based counterparts, producing significantly more energy per turbine. As of 2023, offshore wind accounted for about 7% of the world’s total installed wind capacity, with rapid growth driven largely by projects in Europe and China.
How Offshore Turbines Work
Offshore wind turbines operate on the same basic principle as onshore ones: wind spins a set of blades, and that rotation generates electricity. But the machines themselves are much larger. A typical onshore turbine has blades around 170 feet long. The largest offshore turbines, like GE’s Haliade-X, have blades stretching 351 feet, roughly the length of a football field. Bigger blades sweep a larger area, capturing more wind energy per rotation.
The blades connect to a generator housed in a compartment called the nacelle, which sits on top of the tower. Many offshore turbines use a direct-drive design, meaning the blades connect straight to the generator without a gearbox in between. Inside, a giant ring of permanent magnets spins with the rotor at 8 to 20 rotations per minute, passing through stationary copper coils to produce electric current. Skipping the gearbox reduces the number of moving parts, which improves reliability in a harsh ocean environment where repairs are expensive and weather windows for maintenance are limited.
Foundations: How Turbines Stay in Place
The type of foundation anchoring a turbine to the seafloor depends primarily on water depth. Three main designs cover the range of conditions found in offshore wind development.
- Monopiles are the most common type. A single large steel tube is driven deep into the seabed, suitable for shallow waters between 5 and 55 meters deep. Their simplicity makes them relatively fast to install.
- Jacket foundations resemble lattice towers, anchored by multiple piles. They handle water depths of 30 to 100 meters and distribute forces more effectively in deeper, rougher conditions.
- Floating foundations are used where the water exceeds roughly 60 meters and fixed structures become impractical. Instead of being driven into the seabed, these platforms float on the surface and are held in position by mooring lines. Designs include spar-buoys, semi-submersibles, and tension-leg platforms.
Floating technology is still relatively new at commercial scale. Japan’s first commercial floating wind farm, a 16.8-megawatt project using eight turbines on hybrid spar-type foundations, entered operation recently. Projects like these are opening up vast stretches of deep ocean that were previously off-limits to wind development.
Getting Power to Shore
Generating electricity miles out at sea is only useful if it can reach the grid on land. Subsea cables handle that job. Turbines within a wind farm are connected by cables that route electricity to an offshore substation, which steps up the voltage for efficient long-distance transmission. From there, a high-voltage export cable runs along the ocean floor to a connection point onshore.
These cables are buried beneath the seabed where possible, but they remain vulnerable to damage from anchors, fishing gear, and shifting sediment. Routine surveys using autonomous underwater vehicles and other monitoring tools help operators catch problems before they cut power output. As one oceanographer at Woods Hole Oceanographic Institution put it, the subsea cables that bring power to land are just as important as the spinning blades themselves.
Why Offshore Wind Produces More Energy
A key metric for any power source is its capacity factor: the percentage of its maximum possible output that it actually delivers over time. Onshore wind turbines typically achieve capacity factors of 35 to 40%. Offshore turbines regularly surpass 50%, with Scotland’s Hywind floating wind farm hitting 56%. That gap exists because ocean winds blow faster and more consistently than winds over land, where hills, buildings, and trees create turbulence and friction.
This higher output helps offset the greater cost of building at sea. The U.S. Energy Information Administration estimates that new offshore wind projects entering service in 2030 will have a levelized cost of about $126 per megawatt-hour on a capacity-weighted basis (in 2024 dollars). That’s more expensive than onshore wind or solar, but the premium buys access to a resource that generates power more reliably and during hours when other renewables may fall short.
The Largest Projects Operating Today
The United Kingdom dominates the list of the world’s biggest offshore wind farms. Hornsea 2, off the Yorkshire coast, leads with a capacity of 1,320 megawatts. Hornsea 1, its neighbor, follows at 1,218 megawatts. Dogger Bank Phase A, also in UK waters, rounds out the top three at 1,200 megawatts. Each of these single wind farms can power well over a million homes.
China is the fastest-growing market. In 2023 alone, China added 5 gigawatts of new offshore wind capacity, part of a total 76 gigawatts of wind power (onshore and offshore combined) installed that year. European countries, particularly the UK, Denmark, and the Netherlands, continue to expand their fleets as well.
Effects on Marine Life
Building and operating wind farms in the ocean affects the surrounding ecosystem in several ways. During construction, driving monopiles into the seabed produces intense underwater noise that can disrupt the behavior and hearing of marine mammals, fish, and other species. Most permits for offshore wind construction authorize what regulators classify as “Level B harassment,” meaning temporary hearing sensitivity changes or behavioral disruption rather than physical injury. To reduce noise, developers are often required to use sound-dampening technology like double bubble curtains around the pile during installation.
Once operational, turbine foundations create a “reef effect.” Hard underwater surfaces attract mussels, barnacles, algae, and eventually fish, essentially forming artificial reefs in areas that were previously open sand or mud. Whether this shift in habitat is a net positive or negative for local ecosystems is still being studied.
Other concerns include electromagnetic fields from subsea cables, which could interfere with fish navigation and communication, and increased vessel traffic during construction and maintenance, raising the risk of ship strikes on marine mammals. Corrosion protection systems on underwater structures can also release trace contaminants that marine organisms may absorb. NOAA Fisheries is actively partnering with research groups to track how fish populations respond to turbine installation, including a study off the coast of Virginia monitoring construction noise impacts in real time.
Floating Wind and Deep-Water Expansion
Most of the world’s best offshore wind resources sit over water too deep for fixed foundations. Floating platforms solve this problem by tethering buoyant structures to the seabed with anchoring systems rather than rigid steel tubes. This opens up areas like the U.S. West Coast, the Mediterranean, the waters off Japan and South Korea, and much of the Atlantic where depths drop off quickly.
The technology is moving from demonstration to commercial scale. Japan’s hybrid spar-type floating farm proved the concept works for sustained power generation. In Europe, the Celtic Sea is emerging as a major floating wind zone, with projects planned at scales exceeding 1.5 gigawatts. As manufacturing scales up and installation techniques improve, floating wind is expected to follow the same cost-reduction curve that made fixed-bottom offshore wind competitive over the past decade.