Offshore wind farms are groups of wind turbines clustered together, but situated in coastal waters, typically within 100 nautical miles of land. Locating wind turbines offshore has a number of benefits:
- Offshore winds tend to be stronger and more consistent that onshore
- Over 50% of the population of the US lives in coastal regions
- Wind turbines don't compete with other land uses
- The concern over wind farms as an eyesore is greatly reduced
The biggest challenge with offshore wind is cost, including the additional costs associated with the turbine foundations, advanced materials to resist corrosion, installation that requires special marine vessels, buried subsea cables to bring the power to shore, and offshore maintenance costs. These additional costs can be mitigated by the use of larger turbines than might be desirable onshore, which reduces the cost per kWh. See OWOE: What are the key technology advances impacting wind energy production?
for information on the dramatic increase in turbine sizes over the last two decades.
In shallow water a wind turbine can be supported directly on the sea floor using a monopile structure, which is essentially an extension of the turbine shaft. In deeper water the turbine can be mounted on a fixed or floating platform depending on water depth. Figure 1 summarizes the evolution of offshore wind platform types into deeper water based on offshore oil prototypes. With the push into deeper water, numerous companies are developing proprietary designs based off these general configurations (see OWOE: What are the main challenges facing offshore wind power?
The majority of offshore wind farms are concentrated in Europe in the North Sea, as shown in Figure 2. This data, from 2020 shows China lagging the UK and Germany but projects rapid growth such that by 2022 China in fact becomes the largest offshore wind producing country. The US has been slow to capitalize on it's offshore wind resources, but it is estimated by the NREL
that offshore wind has a technical resource potential of 1.5 terawatts of energy from fixed-bottom wind farms and 2.8 terawatts from floating offshore wind farms across eight geographic areas in the contiguous United States. That total of 4.3 terawatts is approximately four times the total generating capacity of the US grid. Figure 3 shows the NREL's estimate of each region's wind generating capacity.
The first offshore wind farm to start operation in the US was Deepwater Wind's Block Island Wind Farm
. This is a 30-megawatt offshore wind farm located approximately three miles southeast of Block Island, Rhode Island, consisting of 5 turbines on fixed foundations. Offshore installation began in the summer of 2015, and first electricity was generated in December 2016. The second US offshore wind energy project is the Coastal Virginia Offshore Wind (CVOW) project
, located about 43 km off the coast of Virginia Beach, Virginia, U.S. An initial phase, a two-turbine, 12-MW pilot project was constructed and started electricity generation in 2020. When the full project is complete in 2026, it will have a capacity of 2.6 GW. However, US offshore wind power is expected to increase significantly over the next decade. The Vineyard Wind 1 project
, an 800 MW development, located offshore Massachusetts, is under construction and will be the first commercial scale offshore wind project in the US when it comes online in 2023. There are an additional 15 offshore projects that have reached the permitting phase. Figure 4, taken from the DOE "Offshore Wind Market Report: 2022 Edition
" shows the pipeline of offshore wind projects across the US.
Offshore wind has primarily been focused on shallow water developments using fixed foundations. However, given that many future sites for development are in regions of the world with sharply sloped seabeds, such as off the West coast of the US and Hawaii, attention has begun to focus on floating wind platforms. Principle Power built and tested a prototype floating wind platform, called WindFloat 1
offshore Portugal in 2011. After 5 years of successful testing, they developed the 3 platform, 25 MW Windfloat Atlantic Project
in the same area with first power in 2019. However, the first commercial floating wind farm, Hywind Scotland
, was developed by Equinor. It consists of 5 spar-type platforms
supporting 6 MW offshore turbines and anchored in water depths between 90-120 meters. The turbines were installed on the platforms in a Norwegian fjord (see Figure 5), and the completed units were towed across the North Sea for installation offshore Peterhead, Scotland, and began commercial operations in 2017.
Global offshore wind installations had a record year in 2021 with approximately 18 GW of new projects completed, resulting in global installed capacity exceeding 50 GW. Of these, there were three floating offshore wind projects totaling 57.1 MW, including the largest floating offshore wind project built to date - the 50 MW Kincardine Offshore Wind Farm
in Scotland developed by Norway's Statkraft and utilizing Principle Power's WindFloat platforms.