Wind energy is electricity created from wind, a renewable energy source. We can build wind farms on land or offshore, where higher wind speeds prevail.
The foundation supporting the wind turbines is easy to imagine and engineer on land. In relatively shallow water, most offshore wind farms use fixed-foundation wind turbines. However, floating wind turbines have gained popularity in deep waters and are relatively new.
This article shall explain the foundations used in wind turbine towers erected on land and at sea.
The primary function of a wind turbine foundation is to transport and distribute loads to the soil at depth. Gravity and wind are responsible for the turbine foundation’s vertical and horizontal forces acting.
Approach to Wind Turbine Foundation
Wind turbines are often used to generate wind-powered electricity. Turbines create electricity by a spinning motion. Therefore, stability is critical and is ensured by providing an appropriate wind turbine base.
As wind turbines get taller, the wind speed contracting the turbine goes up. The wind force acting on the turbine produces a significant moment at the foundation base level. Every structure’s design aims to determine the sizes and types of components. Foundations should be appropriate and safe for the applied loads and environmental impact of wind farms.
The failure probability of any structure is determined by the material strength and loading taken into account in the design, along with material strength and partial safety elements, the geotechnical. Foundations and soil conditions are also critical in achieving a safe design and structural stability that will last long.
Selecting a wind turbine foundation is a very complex decision that must take into account numerous elements, including:
- Manufacture
- Installation
- Operation
- Environmental Impact
- Levelised Cost Of Energy
What Is The Foundation Of A Wind Turbine?
In general, foundations are simple concrete blocks called footings placed beneath building walls and columns or beneath the tower in the case of wind turbines. The strength and compressibility of the soil or rock beneath the footing determine the performance of this type of foundation.
The size and depth of the footing are affected by the soil or rock conditions. Foundations may require pilings to transfer the load to a deeper stratum with greater strength where soft soils exist. Therefore, foundations are critical to the success of a wind turbine project.
Characteristics of Wind Turbine Foundations
Depth
Geotechnical conditions and structural requirements determine the slab foundation size for giant onshore turbines. A typical slab foundation for a 1 MW turbine would be 15 m in diameter and 1.5 – 3.5 m in depth. The foundation of a turbine in the 1 to 2 MW range typically uses 130 to 240 cubic meters of concrete.
For offshore wind turbines, they are attached to the seabed by mooring lines. In contrast, most turbines are anchored to the ocean floor on fixed foundations, limiting them to roughly 165ft. These massive buildings are built on land and then towed out to sea by boats.
Height
Wind turbine towers can reach 80 meters (260 feet). The blades can be 45 meters (150 feet) long. Keep changes in obstacle height in mind as well. For example, if your trees can grow up to 60 feet tall, a 100-foot turbine tower is recommended.
Soil Properties
The soil should have sufficient bearing capacity to support such massive load capacity. In general, weak/soft soils have little bearing ability. Therefore you should not use these locations for construction foundations.
Types of Onshore Wind Turbine Foundations
After determining the tower height and soil composition, you can decide if the wind turbine tower is supported by a spread footing or a monopile foundation.
Spread
The loads from the wind turbine tower are distributed to the soil by a spread foundation. The reinforced concrete is utilized in the construction of a spread footing. It is similar to a slab foundation in that it comprises a large plate with a large area for spreading loads to the ground. The shape used in the spread footing is usually cylindrical or a square prism.
Monopile
A monopile foundation consists of a steel or concrete plate that links the pile cluster and the wind turbine tower. The plate width should be chosen so that the piles do not interfere. Piles can sometimes be driven to greater depths to minimize tension load problems.
Types of Offshore Wind Turbine Foundations
Offshore wind turbine structures (OWTs) are dynamically sensitive due to their shape and form and the many driving functions (wind, wave, and turbine loading).
The cost of fixed offshore wind farm foundations rises considerably with the depth of the sea rising from shallow to deep waters. Gravity and monopile foundations are widely employed in shallow waters. It would help if you chose an appropriate foundation wind turbine type based on the building location of wind farms in the offshore regions.
Gravity
Gravity-type foundations, which draw stability from their weight, were the first foundations utilized in offshore wind projects. It comprises a giant circular pile with a concrete plate structure lying on the bottom, particularly in shallow waters near the shore.
Monopile
Monopile foundations have grown in popularity recently, particularly offshore wind farms in the UK. North Sea wind farms commonly use monopiles for the following reasons:
- Installation in shallow waters at a depth of fewer than 30 meters
- The soil accessible on wind farms is sand and gravel
- Low effort to drive the piles
This monopile foundation system is the most cost-effective at water depths less than 30m and seabeds of sand and gravel. In addition, it can reduce material maintenance costs.
Suction Caisson
Suction caisson foundations are environmentally benign since they do not require heavy machinery for piling or installation. This foundation structure produces no high-level vibration, noise, or suspended sediment. It appears similar to an upside-down bucket. In addition, it is an affordable foundation approach because we can install it quickly and easily.
Jacket
Jacket foundations in space frames can offer the requisite strength and stiffness. In addition, it is efficient in transitional water depths with a relatively low penetration length.
Twisted jackets are more expensive and challenging to produce and install than other types of jackets. The crooked jacket foundation has been tested with a metallic mast. Still, the wind turbine industry’s proven technology test has not yet passed.
Floating
Floating foundations are incredibly competitive in deep water, where traditional bottom-supported structures are uncompetitive. In terms of cost, construction, and installation, floating structures have numerous advantages in deep waters.
Potential Of An Offshore Wind Energy
According to the National Renewable Energy Laboratory, we could install 5 megawatts of wind turbines in every square kilometer of water in high impact areas. In addition, detailed resource maps and data for offshore wind resources in 26 coastal states break down wind energy potential by wind speed, sea depth, and distance from shore.
Wind Resources
The peculiarity of offshore wind development resources includes a range of spatial and temporal scales, field data on external circumstances, and the energy per sea area is roughly independent of turbine size.
Water depth, currents, seabed, migration, and wave action are essential data points influencing mechanical and structural loading on various offshore wind foundations.
Other issues to consider are marine growth, salinity, icing, and the geotechnical properties of the sea or lake bed.
Assembly
The most challenging element in raising a floating wind turbine is securing them to the seafloor. First, a steel cylinder known as a monopile is fastened to the sea bed and sunk 30 meters deep. Then, a gravity foundation is employed for an ocean depth of 30 meters. This floating offshore wind foundation comprises a large concrete or steel platform with a diameter of approximately 15 meters and roughly 1,000 tons.
Developers can build deeper installations by employing a jacket or foundation with a lattice framework, similar to an antenna tower, with 3 or 4 legs fixed to the bottom. But, of course, we must also consider the seafloor composition.
Environmental Considerations
While wind turbines make clean, green energy from wind power, they also show the negative environmental impact of wind energy. Offshore structures may alter adjacent fish distributions. Wind farm developments may produce an artificial reef, affecting marine species richness.
The chances of catching marine life, in particular, would be significantly diminished. Aside from the blocking effect, the noise and electromagnetic fields around working wind turbines may hurt fish.
Conclusion
Ultimately, through the examination of various types of foundations for onshore and offshore wind farms, it is evident that gravity-type foundations can efficiently withstand loads and are most practical, particularly in shallow waters and on land.
In addition, it is clear that a wind turbine’s foundation is one of its most critical components and must be able to survive extreme weather conditions as the structure that anchors the wind turbine.
Furthermore, the potential use of offshore wind farms is enormous, and their applications could play an essential role in any country’s attempt to reduce its dependency on fossil fuels and choose renewable energy over conventional energy. Wind energy has been proven to be one of the cheapest alternative sources even with the high construction and installation costs, especially in offshore wind turbines.