Offshore wind in China
China has made slower progress than planned in the installation of offshore wind capacity since the commissioning of its first turbine in 2007. The majority of projects reside within the nearshore intertidal zone and little experience outside this zone has been gained. The rate of progress is now increasing and the Government has specified that new projects should be further offshore in deeper waters. Much of the East coast of China has good to excellent wind energy resource and shallow waters extend for tens of kilometres from the shore. Soft ground conditions and the occurrence of typhoons complicate the otherwise favourable conditions for offshore wind development.
Author(s): Samuel Jeddere-Fisher
To overcome these local challenges, Chinese developers have tested a range of different foundation types including unique approaches such as high-rise pile cap foundations. Installation techniques, vessels, and wind turbines have been developed to suit the local conditions and these have been supplemented by methodologies and equipment from the European offshore wind industry.
In 2014, China had the fourth highest installed capacity of offshore wind in the world, accounting for 7.5% of the global total . Over two-thirds of this capacity is installed in the intertidal zone. The growth rate of the sector (Fig 1) is comparable with that of Europe as a whole during the early years of European growth after the year 2000. In 2011, China's National Energy Administration (NEA) published a target of 5 GW of offshore wind by 2015 and 30 GW by 2020. Despite a high growth rate, the 2015 target has been missed by a significant margin.
Fig 1: Offshore wind installed capacity in China [2, 3]
China has different wind characteristics, ground conditions, and installation facilities to Europe and so has had to develop its own offshore wind industry to suit. China's developers have experimented with a wide range of turbines and foundations, providing them with broad experience of the advantages and disadvantages of each.
Offshore wind resource and water depth
The offshore wind resource in China is greatest off the coast of the provinces of Fujian and Zhejiang, where it is comparable with that of offshore sites in northern Europe, with wind power densities from 550 to 1000 W/m 2 at 100 m height (Fig 2). This corresponds to mean wind speeds of ∼7.5–9.5 m/s.
Fig 2: Wind power density (watt per square metres) at 100 m height and water depth contours on the East China coast 
At the centre of the Bohai Sea, the wind power density varies from 450 to 650 W/m 2 at 100 m height. The Bohai Sea has a mean depth of around 20 m, and a maximum depth of 70 m.
The coast of the Jiangsu and Shandong provinces that faces out toward the Yellow Sea has wind power densities from 350 to 500 W/m 2 at 100 m height. The water depth is favourable, with areas <25 m deep that extend up to 160 km from shore. This coast also has extensive intertidal mud flats.
The waters around the island province of Hainan have similar resource to that on the coast of the Yellow Sea; however, the water depth increases quickly away from the shore and there is only a thin strip of coast with depths of <25 m.
The total exploitable offshore wind resource up to a depth of 50 m in Chinese waters has been estimated at 500 GW  at a 70 m hub height. About 200 GW of this is estimated to be within water depths <25 m .
Fig 3: Offshore wind farms commissioned and under construction in China as of August 2015 
Offshore wind projects installed and under construction
The first offshore wind turbine was installed in China in 2007 onto a disused offshore hydrocarbons platform. The first commercial offshore wind farm, the Donghai Bridge 102 MW wind farm, was installed in 2010 southeast of Shanghai. Installed cost of the wind farm was ¥23,000/kW, almost double the cost of UK Round 1 offshore wind . The high cost is due to the use of available but expensive assets for the foundation construction and turbine installation . A feed in tariff (export price + subsidy) of ¥0.978/kWh was agreed, nearly double the tariff paid to onshore wind farms in China . The capacity factor for the Donghai Bridge wind farm was 25.3% in 2011 and 27.5% in 2012 .
Following the Dong Hai project, development has been concentrated in the Rudong area of the Jiangsu Province (see Fig 3), with a total capacity of over 250 MW installed by 2014 . Despite not having the best wind resource, the area is out of the main typhoon path and consists of large areas of intertidal mudflats close to shore which enabled installation using existing construction equipment and vessels.
The China Longyuan Power Group Corporation (CLYPG) is the major developer of offshore wind in the Rudong area, having started with the Longyuan Rudong intertidal trial project. This project, which commenced in 2009, was unusual as it featured 11 types of turbines, and multiple types of foundation including gravity base, high-rise pile cap, and tripod type designs . The project was used to allow the developers, turbine manufacturers, and installers to gain experience and test designs without committing to a full wind farm. Extension of the trial site began in 2013, again with a variety of turbines and foundations including 5 MW+ wind turbines.
CLYPG has continued development in the area. Following completion of the projects under construction in 2015, CLYPG's total capacity in the area is expected to be just under 500 MW. Further details on the CLYPG's Jiangsu Rudong intertidal demonstration wind farm can be found in the case study. CLYPG has also developed a 33 MW wind farm in intertidal waters close to Tianjin using 1.5 MW turbines supplied by Guodian United Power .
The Rudong area is also being developed by other companies, with over 200 MW currently being installed. Further developments are also planned, with projects moving further offshore out of the intertidal zone.
Two wind farms are currently under construction off the Fujian coast, the 16 MW Longyuan Putian Nanri Island phase 1, consisting of Siemens 4 MW geared turbines and the 50 MW Putian Pinghai Ba demonstration phase A, consisting of ten XEMC-Darwind 5 MW direct drive permanent magnet variable speed turbines. Both of these turbines are rated to International Electrotechnical Commission (IEC) Class I wind conditions .
The construction of the Zhuhai Guishan demonstration 200 MW wind farm has started off the coast of Guangdong. This will consist of a mixture of Guodian United Power and Mingyang wind turbines, all of 3 MW rating .
The current feed in tariff (export price + subsidy) is set at ¥0.75/kWh for intertidal sites and ¥0.85/kWh for nearshore sites, which many developers claim is too low and does not take into account regional variation in project costs . The feed in tariff is still significantly higher than the tariff paid for electricity from thermal sources, which is around ¥0.36/kWh .
Typhoons and their effect on wind turbines
Typhoons are tropical storms that develop in the northwestern Pacific Ocean, often making landfall in the Philippines, Taiwan, and China. An average of 17 typhoons develop in the northwestern Pacific Ocean each year and typically, five to six of these could be expected to make landfall on China's coast . Table 1 shows the breakdown of typhoon landfalls per province.
Table 1: Mean annual typhoon landfalls per Chinese province
Mean annual typhoon landfalls (1945–2003) 
Whilst the occurrence of typhoons increases the statistical mean wind speed along much of China's coastline, it places additional requirements on the design of wind turbines and their foundations. Analysis of typhoon records suggest that sustained (10 min mean) wind speeds at 10 m above sea level during a 1 in 50 year return event along the Hainan, Guangdong, Fujian, or Zhejiang coast could be up to 45 m/s .
At a typical offshore wind turbine hub height of 80 m above sea level, this equates to a maximum sustained wind speed at the turbine hub height of ∼60 m/s, estimated with the wind profile power law. This is 10 m/s higher than the wind speed defined in ‘Class I’, the highest wind speed class, of the IEC standard for wind turbines . Offshore wind turbines in China have survived a number of typhoons; however, there have been cases of damage to onshore turbines.
In addition to high sustained wind speeds, typhoons may also cause rapid changes in wind direction, high gust speeds, storm surge, and unusual wind shear and wind/wave combinations .
Environmental and legislative factors affecting wind farm locations
The Bohai Sea, in the northeast of China, is one of the world's busiest seas for shipping, with at least seven major ports located within or adjacent to it and also contains China's most abundant offshore oil and gas field. These factors could limit offshore wind development in the area. Similar constraints are present along much of China's coastline, particularly as a huge proportion of China's population reside along its East coast. Communities are reliant on the sea for fishing, energy, and transportation and so there are many stakeholders to consider in the site selection and consenting of projects. A benefit of the dense population is the proximity of the coastline to large load centres and the availability of sufficient grid capacity for the connection of wind farms.
Tourism is an important part of the economy on the island province of Hainan. This could limit opportunities for offshore wind due to the visual impact of the turbines from the island's coastal resorts.
In 2011, the NEA issued a regulation stating that new offshore wind farms should in principle be installed in locations >10 km from the shore. Additionally, where the intertidal mud flats extend further than 10 km from the shore, the water depth at the location should be >10 m . Development in marine nature reserves, environmentally protected or sensitive areas, areas with important fisheries, or areas close to natural monuments will also be restricted.
Grid connection of offshore wind farms
China's East coast has a well-established electrical distribution system to meet the high industrial and domestic demands of the area. A number of ultra-high-voltage (UHV) connections, at 1000 kV alternating current (A.C.) or ±800 kV direct current, allow power to be transferred between China's regional grids, and more UHV connections are currently being constructed and planned.
Most offshore wind farms in China are connected directly to the shore via subsea A.C. cables operating at 35 kV. The voltage is transformed to 110 or 220 kV A.C. at an onshore substation before connection to the grid. This is a similar approach to many early European offshore wind projects which did not have an offshore substation.
The first wind farm in China to use an offshore substation will be the 202 MW Xiangshui demonstration project in Jiangsu Province, for which installation started in 2015. ABB will supply equipment for the substation which will transform from the inter-array voltage of 35 kV to 220 kV for transmission to shore and connection to the grid .
In 2011, the General Administration of Quality Supervision, Inspection and Quarantine issued the Chinese national standard, GB/T 19963-2011 Technical rules for connecting wind farm to power system, which covers power quality, active and reactive power performance, generation forecasting and reporting, model simulations, and field test requirements .
Offshore wind turbine foundations
A wide range of offshore wind turbine foundations have been used in China including types not used in Europe. To date monopile, tripod type (with three or more piles) and high-rise pile cap foundations have been the most common. Gravity base, jacket, and suction bucket foundations have also been used.
The use of high-rise pile caps in offshore wind is unique to China; they were first used on China's first offshore wind farm, at Donghai Bridge, Shanghai. A number of long and thin piles are installed and a concrete pile cap is cast in situ over the top at water level. The pile cap provides some impact protection from vessel collisions. The piles used in high-rise pile cap foundations are smaller than those required for monopile foundations; each of the Donghai Bridge's turbine foundations, for example, used eight piles of 1.7 m diameter and 80 m length. Smaller and less specialist installation vessels can be used to install these piles compared with the vessels and hammers required to install large monopiles. The availability of these vessels in China is one reason for the popularity of this design.
High-rise pile caps were used for all of the first non-intertidal offshore wind farms in China. Jack-up vessels suitable for monopile installation have now been commissioned and monopile foundations have been selected for the China General Nuclear Power Group (CGN) Rudong wind farm, Jiangsu, as installation time and cost are expected to be lower compared with high-rise pile caps. The project's monopiles are up to 6.7 m diameter and 94 m long .
Ground conditions at many of China's existing and proposed wind farm locations are softer than at European wind farms. Mud and silty clay or sand often extends below the sea bed to the full depth of the pile. In comparison, European sites often have denser sand, clay, or bedrock. Tripod type foundations are often used to overcome the problems associated with monopiles in soft material as they provide a greater lateral stiffness. If monopiles are used, large diameter piles and a high penetration depth are required; however, costs are expected to be lower now that suitable installation vessels are available.
Tripod type foundations have been used for some of the foundations at the Longyuan Rudong intertidal trial wind farm and for part of phase I of the Jiangsu Rudong 150 MW intertidal demonstration wind farm. Designs have varied with the number of piles ranging from three to seven .
Transition pieces act as an interface between the turbine tower and foundation and are used to correct minor vertical misalignments of the pile via a grouted connection. Where monopiles have been used in China, they have typically integrated the foundation, transition piece, and secondary steel (Fig 4) rather than having a separate transition piece. The single piece foundation is well suited for use at intertidal sites and does not require specialist grouting equipment. The omission of a transition piece, however, requires the monopile to be installed with a smaller deviation from the vertical than would otherwise be required. Equipment and techniques to enable pile driving of a single piece foundation have been developed by Chinese firms such as Jiangsu Longyuan Zhenhua Marine Engineering Co. Ltd. using specialist equipment such as hydraulic piling hammers supplied by IHC Hydrohammer of the Netherlands. Piles have been installed to a high vertical tolerance, with deviations typically <0.1° from the vertical .
Fig 4: Single pile foundation installed at the Jiangsu Rudong intertidal wind farm. Anodes providing galvanic protection are attached to the pile below the mud line [IHC Hydrohammer]
Foundations located at intertidal locations are at high risk of corrosion due to the frequent exposure to both air and water and the effects of scour increase the likelihood of abrasion to protective coatings at the mudline. Parts of the pile which will be exposed above or close to the mudline are provided with galvanic protection by applying a thermally sprayed metal layer. Marine grade protective coatings are applied to the foundation and additional galvanic protection is provided by sacrificial zinc or aluminium anodes.
The pioneering installation of a suction bucket foundation for an offshore wind turbine was carried out in 2010 off the Jiangsu coast by floating the foundation out to the site. The diameter of the concrete suction bucket skirt was 30 m, with a total foundation mass of over 2000 tonnes . This type of foundation design is well suited to the muddy, soft seabed soils present along much of China's coast and it is likely that these could be utilised on future projects.
Offshore wind turbines
About 12 different turbine manufacturers have installed or are installing wind turbines offshore. The Chinese market is more diverse than Europe's, which is dominated by Siemens and Vestas. The number of turbines installed offshore by the six leading manufacturers is given in Fig 5. The Siemens/Shanghai Electric joint venture leads the market, having gained an early foothold with the installation of 21 turbines in 2011 (Fig 6).
Fig 5: Six manufacturers with the most number of wind turbines either installed or to be installed as part of projects for which construction had started as of August 2015 
Fig 6: Siemens 2.3 MW wind turbines installed at the Jiangsu Rudong 150 MW intertidal demonstration wind farm [http://www.siemens.com/press]
The capacity of offshore wind turbines installed in China ranges from 1.5 to 6.0 MW, with most of the projects under construction in 2015 having turbines rated between 3.0 and 5.0 MW.
The Chinese Government's policy requires both onshore and offshore projects to use turbines assembled in China (this has been relaxed from the requirement for local fabrication). Many Chinese companies have developed their own turbine technologies and are now adapting these designs for use offshore. A few Chinese turbine manufacturers have developed strategic relationships with established European companies. Siemens and Shanghai Electric, for example, entered a joint venture in 2011 to develop and manufacture wind turbines. This allows Siemens to service the Chinese market as its technology is assembled locally rather than being imported from Europe.
Manufacturing of large wind turbine components is well established in China, with Vestas, Siemens, and LM Wind Power, the leading independent manufacturer of wind turbine blades, all having manufacturing bases in China. Titan Wind Energy is a Chinese wind turbine tower manufacturing company that supplies towers to Vestas, GE Wind Energy, and Chinese companies.
Many Chinese manufacturers and project developers source specialist components from outside of China, for example, ABB has supplied generators, converters, transformers, and switchgear to various projects , and Wikov’s flexible-pin gearbox designed by Orbital2 has been installed in Dongfang’s 5.5 MW turbine (Fig 7) .
Fig 7: Dongfang 5.5 MW turbine installed at the extension to the Longyuan Rudong intertidal trial wind turbine test site. A tripod type foundation consisting of five piles was used [Orbital2]
High wind turbine reliability is essential for the successful operation of offshore wind farms. The low capacity factor of early onshore wind farms in China has in part been attributed to utilisation of designs unsuitable for the Chinese environment, a lack of spare part availability, and a lack of turbine manufacturing, commissioning, and maintenance experience . These issues must be avoided to ensure success of offshore wind in China.
Chinese wind turbine manufacturers have obtained certification from international bodies, with at least Guodian United Power, Envision, Mingyang, and Sinovel having achieved turbine certification from DNV GL .
Vessels and installation
Projects in the intertidal zone have used flat bottomed crane barges for foundation and turbine installation. Foundations have been installed at low tide with the crane barge sat on the mud. The availability of these vessels has been a significant driver in the selection of intertidal sites, along with their proximity to the shore. The use of jack-up vessels is problematic at many of the sites in China due to the soft sea bed material; however, installations have recently been carried out using purpose built wind turbine installation jack-up vessels (Fig 8). One example of a purpose built jack-up vessel is the Longyuan Zhenhua II, operated by China Communications Construction Company Limited, fitted with a 725 tonne crane and able to operate in water depths up to 30 m . Owing to the soft sea bed, the footprint of the jack-up legs is usually larger than those used in Europe .
Fig 8: Jack-up vessel operating at the Jiangsu Rudong wind farm in 2014 [IHC Hydrohammer]
The Donghai Bridge wind farm used an installation technique pioneered by the UK's Beatrice demonstration project: turbines were fully assembled onshore and a crane vessel was used to lift the turbines and transport them from the port out to the waiting foundations. The vessel used, Endeavour, is operated by China Communications Construction Company Limited and fitted with a shear leg crane with a total lifting capacity of 2300 tonnes.
Offshore wind in China has grown at a fast rate, though slower than China hoped, with a cost of energy almost double that of onshore wind. The majority of development has occurred on the intertidal sites at Rudong, off the coast of the Jiangsu Province. In addition to further development in the Rudong area, wind farms are being installed off the Fujian and Guangdong coasts where the wind resource is higher.
Monopiles and tripod type foundations have dominated in the intertidal zones, with high-rise pile cap foundations the most popular in deeper water. As experience and availability of installation equipment and vessels improve, developers will be able to select more cost-effective foundation and installation solutions.
The size of China's offshore wind projects continues to increase, and further developmental steps are being taken such as the introduction of offshore substations, and the move to larger capacity turbines. To continue growing, the sector must reduce costs, and continue to overcome new challenges for the offshore wind industry such as the ground conditions and typhoons found in China.
Siemens is the only major foreign company involved in the supply of offshore wind turbines while Sinovel, Goldwind, and Guodian United Power are the leading Chinese manufacturers. Further opportunities exist for technology and expertise transfer between the Chinese and European markets.
- Global Offshore. Available at http://www.gwec.net/global-figures/global-offshore/, accessed August 2015 .
- Carbon Trust: ‘Detailed appraisal of the offshore wind industry in China’ (Carbon Trust, UK, 2014), p. 9.
- China’s Offshore Wind Growth Surges 487.9%. Available at http://www.cleantechnica.com/2015/04/01/chinas-offshore-wind-growth-surges-487-9/, accessed August 2015.
- Copyright © 2011 ‘China Wind Energy Development Roadmap 2050’ OECD/IEA, licence: www.iea.org/t&c/termsandconditions and the ERI. Labels added by the author.
- IEA and ERI: ‘China wind energy development roadmap 2050’ (IEA, Beijing, China, 2011), p. 15.
- Carbon Trust: ‘Detailed appraisal of the offshore wind industry in China’ (Carbon Trust, UK, 2014), p. 10.
- LiuT.Y.TavnerP.J.FengY. et al.: ‘ Review of recent offshore wind power developments in China’, Wind Energy, 2013, 16, pp. 786–803 (doi: 10.1002/we.1523) .
- http://www.fenglifadian.com/news/china/1231A4IE.html, accessed January 2016.
- Yanhui F. Yingning Q. Junwei Z.: ‘Study of China's 1st large offshore wind project’. Renewable Power Generation Conf., Beijing, China, September 2013.
- Wind farm data from 4C Offshore. Available at http://www.4coffshore.com, accessed August 2015 .
- Zhao F.: ‘China offshore wind feed-in tariffs and supply chain implication’ (FTI-CL Energy, 2014).
- http://www.en.sxcoal.com/NewsDetail.aspx?cateID=613&id=138667&keyword=power%20tariff, accessed January 2016.
- Fogarty E. A.: ‘Variations in typhoon landfalls over China’. MSc thesis, The Florida State University, 2004.
- Clausen N.-E. Pagalilawan E.: ‘Design of wind turbines in an area with tropical cyclones’. Proc. European Wind Energy Conf., Athens, Greece, February 2006.
- IEC 61400: Wind turbines – Part 1: Design requirements, 2005.
- NREL and AWS Truepower LLC: ‘Assessment of offshore wind system design, safety, and operation standards’ (NREL, USA, 2014), pp. 25–26.
- CREIA, Greenpeace, GWEC, and CWEA: ‘China wind energy outlook’ (GWEC, 2012), p. 18.
- ABB to provide power products for China's large offshore wind farm. Available at http://www.abb.co.uk/cawp/seitp202/34d45f2fd309178cc1257e060029a03f.aspx, accessed August 2015.
- IEC: ‘Grid integration of large-capacity renewable energy sources and use of large-capacity electrical energy storage’ (IEC, Geneva, Switzerland, 2012), p. 89.
- CGN Rudong Offshore Demonstration Project. Available at http://www.4coffshore.com/windfarms/cgn-rudong-offshore-demonstration-project-china-cn61.html, accessed August 2015.
- Longyuan Rudong Intertidal Trial Wind Farm. Available at http://www.4coffshore.com/windfarms/longyuan-rudong-intertidal-trial-wind-farm-china-cn07.html, accessed August 2015.
- 150 MW Intertidal Offshore Demonstration Wind Farm was Commercially Put into Operation. Available at http://www.clypg.com.cn/en/newscenter/headlinenews/279494.shtml, accessed August 2015.
- Zhang P. Ding H. Le C. et al.: ‘Hydrodynamic motion of composite bucket foundation for offshore wind turbines’. Proc. 24th (2014) Int. Ocean and Polar Engineering Conf., Busan, Korea, June 2014.
- Dongfang Electric 5.5 MW with Orbital2 gearbox. Available at http://www.orbital2.com/index.php/news-single-article, accessed August 2015.
- GL Renewables Certification (GL RC), List of Certifications. Available at http://www.gl-group.com/en/certification/renewables/ListOfCertifications.php, accessed August 2015.
- Wind Power Installation Platform Launched Successfully. Available at http://www.zpmc-netherlands.com/offshore-windfarm/zpmcs-largest-domestic-offshore-wind-power-installation-platform-launched-successfully/, accessed August 2015.
- IHC Hydrohammer, personal communication, August, 2015.
- China Longyuan Power: Wind Vane of Offshore Wind Power. Available athttp://www.clypg.com.cn/en/newscenter/headlinenews/269866.shtml, accessed August 2015.
Jiangsu Rudong intertidal demonstration wind farm
Developed by CLYPG, the Jiangsu Rudong 150 MW intertidal demonstration wind farm is located in the Jiangsu province, 150 km North of Shanghai, on intertidal mud flats. The wind farm has been developed in stages, commencing in 2010 with a trial of nine turbine models from eight manufactures, with multiple foundation types providing an initial capacity of 32 MW. These included turbines with doubly fed induction generators, permanent magnet generators, and MingYang's two bladed turbine .
In 2011, construction of the 99 MW phase I of the project was started, comprising 21 Siemens 2.3 MW turbines and 17 Sinovel 3 MW turbines. Phase II was installed in 2012 and comprised 20 Goldwind 2.5 MW turbines providing a further 50 MW. An additional 50 MW of Goldwind turbines was installed as an extension to the wind farm, with final commissioning in spring 2013 .
A 200 MW extension of the project was approved in 2013 by the NEA. Turbine installation began in late 2014, starting with 25 Envision 4 MW turbines, followed by 25 Siemens 4 MW turbines .
Following the trial of different foundation types in the initial demonstration phase, single or tripod type foundation types were selected for the commercial phases of the project. Before the start of phase I of the project, a dedicated flat bottomed crane barge was commissioned to enable installation of monopile foundations. Other vessels were adapted or commissioned for the wind industry including cable installation vessels, anchor handling boats, and transport vessels. The crane barge was used to install foundations during low tide for the first phases of the project . A jack-up vessel fitted with an IHC Hydrohammer hydraulic pile hammer has been used on the 200 MW extension (Fig 9) .
Fig 9: Jack-up vessel installing monopiles at the 200 MW extension of the Jiangsu Rudong Offshore Wind Farm in 2014 [IHC Hydrohammer]