The best accessible global areas for offshore wind farms, reasonably close to shore and in shallow water, are the North Sea and the South China Sea. See the Global Wind Atlas.
At the end of 2020 UK was the global leader with 10 GW of offshore wind capacity installed, 37% of global offshore wind capacity.
But in 2021 China installed a further 17 GW to take pole position, which it is now unlikely to lose.
Germany, Denmark, Belgium and the Netherlands propose to build 150 GW of offshore wind farms between them by 2050. The proposal includes an energy island to enable power to be flexibly routed.
China is proposing a huge 43 GW offshore wind farm in the Taiwan Straits to provide power to the 13 million inhabitants of the city of ChouZhou, GuangDong province. According to the local plan, work on this is expected to start by 2025.
Offshore wind turbines are typically far bigger than onshore wind turbines, constrained by the maximum turbine size that the industry can produce, rather than planning rules. Whereas 3-4 MW is the limit for most onshore wind turbines, the largest offshore turbine on sale (5 December 2022) is the 16 MW wind turbine developed jointly by China Three Gorges Corporation and Goldwind Technology. It is 270m tall with a rotor diameter of 252 metres, and a swept area of 50,000 square metres, the equivalent of around seven standard football pitches. However, (6 January 2023) CSSC Haizhuang Wind Power has now announced an 18 MW turbine with a rotor diameter of 260 metres and a swept area of 53,000 square metres.
There is very little NIMBY (“not in my back yard”) opposition from householders to offshore wind farms, but the needs of fishermen and other ocean users must be taken into consideration. Environmental assessments are also required.
There are two methods of securing offshore wind turbines to the sea bed. Almost all current offshore wind farms use bottom fixed turbines, with foundations embedded into the sea bed. A handful use floating onshore wind in which the only connection to the sea bed is a cable and anchor. The cable attaches to a float on which the turbine is mounted.
Other designs are possible, but not mainstream.
Offshore wind turbines are generally direct drive, with no variable speed gearbox. The AC output of the generator is thus not tied to a mains frequency of 50 or 60 Hz. If the onshore cable is HVAC, then offshore frequency converters are needed.
Capacity factors offshore are much higher than onshore. Offshore wind farms on the UK part of Dogger Bank (off the east coast of the UK) are expected to have a 60% capacity factor, because of the average wind speed of over 10 m/s. The north and northwest of Scotland have significantly higher wind speeds than Dogger Bank, and should have capacity factors exceeding 60%, but will require floating offshore wind turbines because of the ocean depth.
See the Global Wind Atlas, which can estimate the annual capacity factor for most of the likely locations for wind farms around the world.
RenewableUK has analysed the UK and global offshore wind projects. As of February 2023, the global pipeline of offshore wind projects is 1,100 GW (1.1 TW). Renewable UK says this would provide 20% of global electricity demand.
According to Statista, in 2021, global electricity demand was 25,343 TWh. That is an average of around 3 TW (3,000 GW) of demand. If the average capacity of all offshore wind projects were 55%, then 1,100 GW of offshore wind capacity would result in average generation of 605 GW, which is 20% of 3,000 GW.
But by the time we get to 2030, electricity demand will be higher – maybe 50% higher or more. However, the offshore wind pipeline is also likely to grow over time.
Initial offshore wind projects produced very expensive power.
After initial installations by Denmark, the UK chose to lead the construction of large scale offshore wind farms to achieve mass market status for offshore wind and economies of scale. UK was assisted in this by Germany, Holland, Denmark and other northern European countries. This has reduced the cost of offshore wind considerably over the last seven years.
Since the 2014 CfD (contract for differences = fixed price) contracts were signed, the cost of UK offshore wind has come down 73%.
Some Dutch and German offshore wind CfD (contract for differences) contract strike prices have been for zero euros. However, these countries have a “one way” CfD contract whereby zero just means they will take the normal wholesale electricity price (never subsidised).
The UK has “two-way” CfD contracts which means the electricity generator has to pay back any difference between the wholesale price and the contracted CfD strike price. UK CfD auctions will be annual from now on, likely with 7 GW of offshore wind auctioned each year, as in the 2021/22 CfD auction.
The Dutch and German grids also pay for the cost of the connection from the offshore wind farm to the onshore transmission network. Whereas, in the UK, the offshore connection has to be paid for by the offshore wind project up to the point of connection to the onshore transmission (or distribution) network. So UK offshore wind prices are not strictly comparable with those in the Netherlands and Germany.
The US DoE (department of energy) says the US cost of bottom fixed offshore wind in 2021 was $84/MWh, expected to drop to $60/MWh by 2030.
In China the cost of offshore wind is estimated at $78/MWh, including cabling. Coal power there is estimated to cost $76/MWh, so Chinese offshore wind is now challenging coal on cost.
At the end of 2021, China had 26 GW of offshore wind installed, of which 17 GW was installed in 2021, adding more capacity than the rest of the world had installed over the previous 5 years, and stealing UK’s end 2020 crown of 10 GW of installed capacity.
Germany had 8 GW of offshore wind as of the end of 2022. It has offshore wind targets as follows:-
The German grid picks up the costs of transmission of power from an offshore wind farm to the onshore grid connection.
Germany has one way CfD (contract for differences) auctions for offshore wind. The cheapest bids win the auctions. “One way” means that the the generator has the wholesale market price of power made up to the contracted strike price for the project if the wholesale price is lower. But if the wholesale price is higher than the strike price the generator does not have to pay back the difference.
However this has resulted in many recent zero price CfD auction bids for German offshore wind, which means the generator just takes the wholesale market price. This has resulted in lotteries to determine the winners, with other criteria also being taken into account. This isn’t really satisfactory. The process is being amended but the current proposal is contentious.
Existing German offshore wind capacity factors are listed on this link.
Japan has huge potential for offshore wind power, with around 550 GW possible – mainly with floating offshore wind.
At the end of 2022, the UK had 13.7 GW of offshore wind installed, and a 2030 target of 50 GW offshore wind. Taking into account likely capacity factors, this implies that the 2030 UK grid will likely be 70% powered by offshore wind, with some also available for export.
RenewableUK has analysed the UK and global offshore wind projects. As of February 2023, the UK pipeline of offshore wind projects is 100 GW, broken down as follows:-
UK offshore wind farms capacity factors are listed on this link.
The UK exclusive economic ocean zone has huge offshore wind potential – enough to provide the energy required by the UK in 2050 two to three times over.
UK’s exclusive economic ocean zone is 773,676 sq km and includes Rockall and the Isle of Man. With a conservative estimate of the average offshore wind power density of 300 kW per sq km, this equates to 232 GW average available, which is 2,033 TWh per year. The UK CCC (Committee for Climate Change) estimates the total 2050 UK total energy requirement to be up to 680 TWh per year [p45].
By the end of 2022 the USA had almost no offshore wind installed – 42 MW – but the pipeline of projects is large and extending over time.
However, as can be seen from the NREL US wind map below, the USA has plenty of offshore wind resources on both coasts.
The US Biden administration has a target of 30 GW of offshore wind by 2030, plus 15 GW of floating offshore wind by 2035. Most of the US coastline is suitable for bottom fixed offshore wind, but northern California, Oregon and Maine have steeply sloping sea bottoms for which floating turbines will be required.
Most US coastal states have shown strong interest in offshore wind.
The US BOEM (Bureau of Ocean Energy Management) has issued a list of offshore wind leases and a lease area atlas. California has just concluded an auction of floating offshore wind and there are a number of lease auctions coming up.
The US IRA (inflation reduction act) provides for a 6-30% tax break for offshore wind farms. The higher amounts require the project to conform to certain wage and apprenticeship provisions.
Also see the links in the main text.