On June 26, 2024, China's independently developed "18MW semi-direct drive offshore wind turbine" was successfully connected to the grid and started generating electricity at the offshore wind power test base in Shantou City, Guangdong Province, once again setting a new world record for the largest single-unit capacity of grid-connected wind turbines. The domestication rate of the components of this unit has reached 100%, with an average annual power generation of 72 million kW hours, which can meet the annual electricity consumption of about 40,000 households.
On June 5, 2024, the 18MW high-power semi-direct drive offshore wind turbine was successfully hoisted at the offshore wind power test base in Shantou City, Guangdong Province. Photo source: Dongfang Electric Corporation.
A few days later, on June 30, China's independently developed "18MW medium-speed integrated offshore wind turbine", after more than a year of comprehensive testing and verification, was successfully hoisted at the Huaneng Xianren Island Thermal Power Plant in Yingkou, Liaoning, marking the wind turbine that created the "two global firsts" record (rotor diameter of 260 meters, single-unit power of 18MW) is about to be put into commercial use.
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Offshore wind power technology research is an important means for China to achieve energy security and build a strong maritime country in line with national strategic needs. More than ten years ago, China's offshore wind power industry had just started. Now, China's wind power has led the global trend of large-scale wind turbines, with self-branded products being continuously updated, taking the lead in entering the "no man's land" of wind power technology and industry development.
Wind Turbine
"Big" is the trend
For high-rise buildings, bridges, and industrial products such as televisions, as technology develops, their sizes have gradually increased, and the same is true for wind turbines. In 1981, the power of the world's largest wind turbine was only 55kW, and this figure only slowly rose to 500kW in 1995, reaching 2MW in 1999. However, since then, the rated power generation of wind turbines has continued to rise: 5MW, 8MW, 10MW, 15MW, 18MW, 20MW, and even 22MW. At present, there is no sign of slowing down in this large-scale development trend.
How does the power of large wind turbines continue to grow? The answer is: the constantly lengthening blades. Larger blades can extract energy from a larger area of wind when rotating, thereby generating more electricity. The power generation of the generator is directly related to the area swept by the rotating blades.So, why are the sizes of wind turbines increasing at such a rapid pace? An article titled "Wind Turbines: How Big?" published in the November 2019 print edition of Nature, explores this question. Professor Simon Hogg from the Department of Engineering at the University of Durham in the UK explains that there is only one core reason, which is to reduce energy costs.
As the size of wind turbines increases, their design, manufacturing, transportation, installation, and maintenance costs will also increase, and the power generation will be significantly enhanced. According to a large amount of unit data currently available, the larger the unit size, the lower the unit average electricity cost (the ratio of power generation revenue to total cost per kilowatt-hour). It is precisely because of this rule that wind turbines continue to grow larger.
"Balanced" development
Break through technical bottlenecks
Longer blades will generate more power, but we must consider strict physical laws. Due to gravity and other factors, there is a limit to the size of any object on Earth. Wind turbines are no exception, and the size of the blades cannot be increased indefinitely.
Firstly, weight is the first factor to consider. The weight of the blade increases with the cube of the blade length. At the same time, to ensure the reliability and safety of the structure, various components need to be reinforced with more materials, which will add extra weight and bring greater challenges to the design of large units. Each blade of the 10MW unit of Danish Vestas Company weighs 35 tons, and the nacelle reaches nearly 400 tons; the unit that General Electric in the United States is about to launch will install blades weighing 55 tons, a nacelle weighing 600 tons, and a tower weighing 2550 tons.
Secondly, the limits of material performance need to be considered. In theory, only the structural bearing performance of the wind turbine blade materials is sufficient to support its continuous growth. At present, the main beam of the wind turbine blade widely uses the carbon fiber material system (which can be said to be the strongest material system). There is almost no better choice for the future blade materials. Based on the limit of carbon fiber, we roughly estimate that the largest blade will soon exceed 150 meters, and some people predict that the limit of the blade length is 275 meters.
Again, the loss situation needs to be considered. Based on the current design (assuming that the air is incompressible), the linear speed of the blade tip must be limited to 90 meters per second, so the larger the rotor, the slower the rotation. But even so, the high-speed movement of the blade tip will cause the blade to collide with raindrops and waves, posing a serious risk of erosion. Within three years, the shape of the front edge of the offshore wind turbine blade will be damaged, and the power generation efficiency will be significantly reduced.
Finally, the transportation issue cannot be ignored. Each blade of the approximate "Big Ben" size must be transported as a whole, which requires huge ports, giant ships, and cranes. Due to the limitations of road width, culverts, and other conditions on land, the transportation of land blades has entered a "bottleneck," and currently, ultra-large wind turbine blades are all installed offshore."Large-scale" Future
Leading "Extreme" Sizes
The process of continuously increasing the size of wind turbines also highlights various issues. At present, engineers only extend the blades and raise the tower, and reinforce the core components. There has been no change in the design concept, such as the large and small turbines with a size difference of 10 times, which are essentially the same.
As the core component of wind turbines, the blade is always an indispensable part in the process of large-scale development of the turbine. The mainstream wind turbines use a three-blade method, but in fact, two blades can also absorb roughly the same wind energy and generate similar power. Obviously, if the wind turbine adopts a two-blade scheme, its overall weight will be greatly reduced, and the length of the blade will also increase accordingly. However, the two-blade scheme will produce serious unbalanced loads, which is not conducive to the long-term stable operation of the turbine, which is the reason why it rarely appears in the market.
In response to the problem of blade transportation, the most direct and effective solution is to divide the blade into two or more sections. Compared with a single blade, in order to ensure the reliability and safety of the segmented connection area, the weight of the segmented blade is often heavier, and the load level is higher, which is not friendly to the large-scale development of the turbine, and the design difficulty is greater. Despite this, several wind power companies are actively investing in the research and development of segmented blades, which will be introduced in the coming years.
Conclusion
Ten years ago, wind power generation was still an emerging industry, and the mainstream view at the time believed that its commercial operation was not feasible. Now, the wind power industry is occupying the energy and power market at an unprecedented speed. Although the size of wind turbines is continuously increasing, it is foreseeable that their extreme size will approach or reach the limit in the next 5-10 years. Soon, we will witness a new history.