Given Europe’s lead in construction and operation of offshore windfarms, it is tempting to think that the continent has a monopoly on technical innovation – not so said the authors of a presentation at the Wind Europe Summit
According to China’s National Energy Administration (NEA), the Chinese Government had approved as many as 44 offshore wind projects in 11 provinces in China by the end of 2015, which will add a combined installed capacity of 10 gigawatts (GW) by 2020. China’s ambitious goals for offshore wind have made it important that the country learns from the European experience of building offshore windfarms, but site conditions at most offshore windfarms in China are very different from those in Europe. So too is the nature of the supply chain and its maturity. This being the case, China has in many cases had to develop its own technical solutions for offshore windfarms.
So said the authors of a poster presentation given at the Wind Europe 2016 Summit in Hamburg in late September. Dr Wei He, a principal engineer at Statoil in Norway, and co-authors from China described the results of a study led by Statoil, which included a case study into how the Chinese offshore wind industry has developed its approach to mitigating technical and non-technical barriers.
Dr Wei and her colleagues said several innovative technologies have been developed for the conditions found in Chinese offshore windfarms. A new foundation with a concrete cap and eight steel piles was developed for the first Chinese offshore windfarm, Donghai Bridge. This challenging site has strong currents and deep, soft seabed conditions. Phase One of the windfarm used 34 3 megawatt (MW) turbines from Sinovel. The turbines are situated approximately 8–13km from shore in an area with an average water depth of 12m. The currents in the windfarm can exceed 3 m/s, and there is a soft sediment layer of 25m thickness on the seabed. The new foundation technology developed consists of a concrete cap (with a diameter of 14m and height of 4.5m) and eight steel piles (with a diameter of 1.7m and height of 80m driven approximately 68m in the seabed. Operational results have confirmed that the new foundation is both cost-effective and mitigates the deleterious effects of local conditions. Installation of the turbines was also innovative, with two large crane vessels, originally designed for the construction of the Donghai Bridge, used to install the fully assembled wind turbine units.
The second offshore windfarm in China, Rudong, is located in an intertidal zone. Phase One of this project saw more than 200MW installed. The first phase made use of 40 2.5MW Goldwind turbines, 17 3MW Sinovel units and 21 2.3MW Siemens units. For the Goldwind turbines, monopile foundations without transition pieces were installed, and a combination of service vessels and tractors were used for operation and maintenance of the turbines. The operation and maintenance concept needed to take account of the fact that the water depth could vary from 0m to more than 8m in a few hours. Service vessels and tractors are used to transport personnel and equipment to and from the wind turbines. In some places, workers also walk to the wind turbines.
The largest ongoing offshore windfarm project in China is Fujian Nanri, a 400MW windfarm. Here, a total of 100 4MW Siemens SWT-4.0-130 turbines are being installed. Learning from offshore wind experience in Europe, the design of Nanri offshore windfarm explored the potential to ‘co-use’ ocean space with the aquaculture industry in order to achieve cost-effective solutions and to reduce potential conflict with the fishing industry. Aquaculture cages have been proposed to co-use the space in the offshore windfarm. Dr Wei and her colleagues said the co-location of small-scale aquaculture with the turbines is expected to yield valuable insights into opportunities to do so elsewhere. “Using offshore wind technology has the potential to help accelerate the movement of aquaculture to open-water sites where the water quality is better,” said the authors of the presentation, noting that combining offshore windfarms with aquaculture “meets the challenge of producing clean energy and high quality seafood whilst minimising environmental impact”.