Wind energy is harnessed by two distinct methods: onshore systems built on land, and offshore systems constructed in bodies of water. While onshore wind farms are generally less expensive to develop and maintain, the industry is increasingly focused on offshore development. This shift is driven by the specific advantages that offshore locations offer over terrestrial sites. These benefits allow offshore projects to deliver higher energy yields and mitigate conflicts associated with land-based generation. The primary difference lies in the quality of the wind resource available in the marine environment.
The Core Advantage: Superior Wind Resource
The open ocean provides a superior environment for wind energy capture due to the physics of air movement over water versus land. Terrestrial landscapes, with their complex features like hills, forests, and buildings, create surface friction and drag on the wind. This friction slows air movement and causes turbulence, leading to wind that is less consistent and more difficult for turbines to utilize efficiently.
In contrast, the vast, flat surface of the sea offers minimal friction, allowing air masses to move freely. This results in consistently higher average wind speeds, often more than double those found at comparable onshore sites. For instance, offshore average wind speeds can reach 8.9 meters per second compared to around 4.29 meters per second onshore. The wind flow offshore is also far less turbulent and more stable.
This superior wind quality is quantified by the capacity factor, which measures a turbine’s actual energy output against its maximum possible output. Onshore wind farms typically achieve capacity factors in the range of 25% to 45%. Offshore wind farms, benefiting from steady marine winds, consistently reach higher capacity factors, ranging from 40% to over 60%. This higher factor means the offshore turbine generates power closer to its full potential more of the time, making it a more reliable source of electricity.
Mitigating Environmental and Social Conflicts
Moving wind generation out to sea addresses several social and aesthetic challenges inherent to land-based projects. Onshore turbines must be placed in rural or remote areas to access sufficient wind, which often leads to opposition concerning the visual impact on the landscape. Placing turbines far enough offshore usually causes them to drop below the horizon line or appear as small silhouettes, significantly reducing aesthetic opposition from coastal communities.
The distance from shore largely eliminates the issue of noise pollution for residents. Land-based, utility-scale turbines typically produce sound levels in the range of 35–45 decibels when measured 300 meters away. Since offshore wind farms are placed many kilometers from the coast, the sound generated by the operating turbines is inaudible to communities on land. This separation removes the turbines from productive land, avoiding conflicts over property rights, agricultural use, and existing infrastructure.
Scale and Power Generation Potential
The lack of land-use constraints and the superior wind resource combine to enable an increase in the physical scale and total power output of offshore wind farms. Unlike on land, where road and bridge limitations dictate the size of turbine components, the maritime environment allows for the transport of enormous structures by sea. This logistical advantage permits the use of physically larger turbines that are impractical for onshore installation.
Modern offshore turbines often have a power capacity in the range of 8 to 12 megawatts (MW), with heights exceeding 250 meters and blade lengths up to 150 meters. This contrasts sharply with typical onshore turbines, which are commonly rated at 2.5 to 3.5 MW. The ability to deploy these larger, more powerful machines, combined with the space to develop vast farm areas, allows offshore projects to achieve a much higher overall Megawatt capacity per project than their land-based counterparts.