Offshore wind refers to electricity generated by large wind turbines installed in bodies of water, typically the ocean. These turbines capture the stronger, steadier winds found over open water to produce power, then send it back to shore through cables buried in the seabed. Offshore wind currently accounts for about 7% of the world’s total installed wind capacity, with the rest coming from land-based turbines.
Why Wind Is Stronger Over Water
The core appeal of offshore wind is simple: wind blows harder and more consistently over the ocean than it does over land. On land, buildings, hills, trees, and other obstacles slow the wind down and make it more turbulent. Water surfaces are smooth by comparison, so wind flows over them with less friction and fewer disruptions.
The difference is significant. Measurements from a coastal region in France illustrate the pattern clearly: at the same height, wind speed onshore averaged about 5.5 meters per second, rose to 7.25 m/s near the coast, and reached 8.5 m/s farther offshore. Because the energy a turbine can extract increases sharply with wind speed, those numbers translate to roughly 73% more energy production for a turbine placed offshore compared to one on land. Wind speeds generally keep increasing up to about 50 kilometers from shore, with less turbulence and more uniform flow at every point along the way.
Lower turbulence also means less mechanical stress on the turbine blades, which can extend the equipment’s lifespan and improve its performance over time.
How Offshore Turbines Are Built
Modern offshore wind turbines are substantially larger than their onshore counterparts. The average offshore turbine stands about 124 meters tall at the hub (where the blades connect to the central shaft), compared to 103 meters for a typical U.S. onshore turbine. Rotor diameters on the largest offshore models now exceed 100 meters, and individual turbines can generate 10 megawatts or more, enough to power thousands of homes each.
The foundation holding these turbines in place depends on how deep the water is. In shallower areas, turbines sit on fixed structures anchored to the seabed. The most common types include monopiles (single large steel tubes driven into the seafloor), jacket foundations (lattice-like steel frames), gravity-based structures (heavy concrete bases that sit on the bottom), tripods, and suction buckets. Each design suits different seabed conditions and water depths.
In deeper water, fixed foundations become too expensive or technically impractical. That’s where floating platforms come in. These designs let the turbine float on the surface while moored to the seabed with cables. The most widely used type is the semisubmersible platform, which sits partially submerged and uses its wide footprint for stability. Floating technology is critical for countries where much of the best wind resource sits over deep water, since it opens up areas that would otherwise be off-limits.
Getting Power to Shore
Generating electricity in the middle of the ocean only matters if you can move it to where people live. Offshore wind farms use a layered electrical system to do this. Each turbine has a transformer at the base of its tower that steps the voltage up from the generation level (around 690 volts) to a medium voltage of 25 to 40 kilovolts. Submarine cables, typically buried one to two meters deep in the seabed, connect all the turbines in a wind farm to a central offshore substation.
At the offshore substation, voltage is stepped up again to 130 to 150 kilovolts for the long trip to shore. A high-voltage submarine cable, also buried for protection, carries the power to land. Once it reaches the coast, the electricity travels through underground or overhead lines to an onshore substation, where it connects to the existing power grid. This entire chain, from turbine to wall outlet, is designed to minimize energy loss over long distances.
Environmental Effects on Marine Life
Building and operating wind farms in the ocean inevitably interacts with marine ecosystems. The biggest concern during construction is noise, particularly from pile driving when foundations are hammered into the seabed. This can disrupt the behavior of marine mammals and temporarily reduce their hearing sensitivity. Mitigation measures during construction typically include using bubble curtains around the pile to dampen sound, timing installation to avoid periods when sensitive species like the North Atlantic right whale are most likely to be in the area, and shutting down operations if marine mammals are spotted nearby.
Once a wind farm is operating, the effects are more mixed. The underwater structures create what’s known as the “reef effect,” where marine life clusters around the hard surfaces of turbine foundations, attracting fish, shellfish, and other organisms that thrive on artificial reefs. On the other hand, the spinning turbines and cables introduce electromagnetic fields that could affect fish navigation and communication. Increased vessel traffic raises the risk of strikes on marine animals. Corrosion protection systems on the structures can also release trace contaminants into the surrounding water.
These effects can influence species’ distribution, behavior, and survival at various life stages, from larval dispersal to spawning. Research is ongoing to understand the cumulative impact as more wind farms are built, particularly in heavily developed areas like the U.S. Atlantic coast.
Maintenance at Sea
Keeping offshore turbines running presents logistical challenges that onshore wind farms never face. You can’t simply drive a truck to a turbine sitting 30 or 40 kilometers out in the ocean. Service operation vessels have become the primary way maintenance crews reach offshore turbines. These specialized ships can house technicians for extended periods and carry spare parts and heavy components needed for repairs.
Weather plays a major role in maintenance planning. Rough seas can delay repairs for days or weeks, so operators carefully coordinate maintenance schedules with weather forecasts. The spare parts loaded onto a service vessel need to be chosen strategically, since budget and storage space prevent carrying everything that might be needed. Getting the right components to the right turbine at the right time is one of the biggest operational challenges in the industry, and allowing emergency resupply trips when an unexpected failure occurs can significantly reduce downtime.
Cost Compared to Onshore Wind
Offshore wind is more expensive than onshore wind. The turbines are larger, the foundations are more complex, installation requires specialized ships, and maintenance involves reaching remote locations in open water. All of these factors push costs higher. In 2024, the cost of offshore wind electricity ticked up about 4%, while onshore wind rose about 3%, driven partly by financing costs and supply chain pressures.
Despite the higher price tag, offshore wind fills a role that onshore wind often can’t. Many of the world’s largest population centers sit along coastlines, and offshore wind farms can be built relatively close to these demand hubs without competing for land. The stronger, more consistent winds offshore also mean turbines produce electricity a higher percentage of the time, which helps offset the added expense. As floating platform technology matures, it will open even more high-wind areas to development, potentially bringing costs down further through economies of scale.