As a power generation method with the most mature technology, the most large-scale development conditions and commercial development prospects in the field of new energy, wind power generation has achieved rapid development. As wind turbines extend from land to sea, offshore wind power is becoming the focus of new energy development.
However, due to the particularity of offshore wind power construction conditions, the basic form of wind turbines is very different from that of onshore wind power, which are briefly described as follows:
1. Gravity foundation
Overview: Mainly rely on its own quality to make the wind turbine stand on the sea.
Advantages: simple structure, low cost and not affected by the seabed, good stability.
Disadvantages: Subsea preparation is required, underwater workload is large, structural integrity and shock resistance are poor, various fillers are required, and the demand is large; the requirements for ships transporting foundation base caissons are high. At present, it is rarely used at home and abroad.
Applicable conditions: only suitable for shallow water areas.
2. Single pile foundation
Overview: Monopile, light weight, simple structure, clear force. The monopile foundation consists of a steel pile with a diameter between 3 and 4.5m. The steel piles are installed 18-25m below the seabed, and the depth is determined by the type of seabed ground.
Pros: No need to tidy up the seabed.
Disadvantages: It is necessary to prevent the erosion of the seabed by the ocean current, which is greatly affected by the impact of tides and surges.
Applicable conditions: The water depth of the application range is less than 25m, and it is not suitable for the position with boulders on the seabed.
3. Tripod base
Overview: Tripod, developed from the light and economical three-leg jacket in the petroleum industry, is composed of cylindrical steel pipes. The central steel tube of the tripod provides the basic support of the wind turbine tower, similar to the monopile structure, the tripod can be supported on steel piles by vertical or inclined casing.
Advantages: The weight of the foundation is light, and the stability of the whole structure is better.
Disadvantages: The leveling control of the foundation needs to be completed with a fixed offshore platform such as a floating dock.
Applicable conditions: The water depth is 15-30m, and it is not suitable for the situation where there are large areas of rocks on the seabed.
4. Jacket type foundation
Overview: Jacket is one of the future development trends of wind farms in the deep sea. Belongs to "Tripod base for meshes". The load of the jacket is carried by piles driven into the foundation.
Advantages: Jacket-type foundation has high strength, low installation noise and light weight, suitable for large-scale wind turbines and deep-sea fields.
Disadvantage: It needs a lot of steel, and it is easy to fail due to the influence of waves, and it is seriously affected by the weather during installation.
Applicable conditions: Suitable for water depths of 15-30m, not suitable for large areas of rocks on the seabed, suitable for waters within 5-50m, which can avoid pouring concrete at sea.
Five, multi-pile foundation
Overview: Also known as "group pile-type high-pile cap foundation", it is a common structure for coastal wharf and bridge pier foundations before being applied to wind power foundations, consisting of foundation piles and upper caps.
Advantages: It is more beneficial to the structural stress and resistance to horizontal displacement.
Disadvantages: The pile foundation is relatively long, and the overall structure is heavy.
Applicable conditions: Applicable water depth 5~20m.
6. Other conceptual foundations
1. Suction foundation
The suction foundation, which is divided into single-column and multi-column suction caisson foundations, etc. The suction foundation draws out the water in the steel skirt caisson through construction methods to form suction. The foundation can greatly save steel consumption and offshore construction time, and has a relatively good application prospect. At present, its feasibility is still in the research stage.
2. Floating foundation
Floating foundation is one of the trends of future deep-sea wind farms. Currently, an experimental unit (Hywind) floating foundation is put into operation 10 kilometers off the coast of southwest Norway. According to reports, Hywind wind turbines can be used in sea areas with a water depth of 120m to 700m, while the current offshore units are basically below 60m. It is expected that the floating foundation technology will mature around 2020.