| Written by Michal Wozniakowski-Zehenter
WIND FARM CONSTRUCTION: Feasibility Study and Site Selection
Extensive research is conducted to determine the viability of an offshore wind farm before its construction. This stage is very important because it lays a foundation for the other stages that will follow. The feasibility study incorporates wind resource assessment, environmental impact studies, and economic viability studies.
One of the biggest site selection factors is the available wind resources. Weather towers, light detection and ranging, and satellites are used to measure available wind speeds at different altitudes over a point in time to determine the potential of wind resources. A minimum threshold average wind speed is usually required for the site to be considered for developing wind energy. The variations also include wind variability, turbulence in the wind, and extreme weather conditions. Offshore areas have stronger and steadier winds, which makes the sites favourable for large projects.
Besides the wind resource, an EIA is carried out looking at how the construction and operation of the wind farm might affect the marine ecosystem. Offshore wind farms have the potential to affect wildlife, including fish populations, seabirds, and marine mammals; noise from pile driving during construction; possible changes in water flow; and electromagnetic fields created by power transmission cables all have ecological effects. The EIA ensures that these risks are identified at an early stage in the process so that project planners can plan mitigation strategies by avoiding specific areas or periods during the year where sensitive species may be present. The stakeholders will include environmental consultants, marine biologists, and local regulatory bodies. Public consultation is also integral to the EIA process, as concerns or objections may arise from local communities and interest groups.
Even if the site demonstrates adequate wind potential and has an acceptable environmental impact, the project has to be viable economically. This assessment would include construction costs, expected energy output, maintenance expenses, and future revenues from energy sales. Offshore wind farms are a huge capital investment, mostly in excess of billions of dollars, which needs underpinning with financing. It is not uncommon to find investors, banks, and governmental bodies coming together with the required funding. Quite often, governments give subsidies and tax incentives or CFD mechanisms to ensure a fixed price for the wind farm's generation of electricity. This helps reduce the project's financial risks.
WIND FARM CONSTRUCTION: Design and Engineering
When the site has been selected, and funds are available, the design and engineering begin. Detailed planning of the construction and operational aspects of the wind farm is done during this phase, keeping in view all the technical, logistics, and safety requirements.
One of the most critical decisions in this stage involves the choice of wind turbines. In this instance, the turbine's size, the rotor's diameter, and the rated capacity are chosen depending on the wind regime conditions of the site. Normally, larger turbines can be recommended for offshore wind farms since higher wind speeds are normally experienced offshore, and more energy can be captured from these winds. The bigger size involves an increase in engineering challenges associated with transportation, installation, and maintenance. The different offshore turbines are designed to work in a hostile marine environment. Special corrosion-resistant materials are used, and their design allows them to operate at high wind speeds combined with salt spray. Manufacturers of such turbines as Siemens Gamesa, Vestas, and General Electric study such factors closely with the project's developers to make adjustments in the specifications of the turbines at the site.
The foundation would be next to the design phase, being the most important. The foundation of an offshore wind turbine must be robust and unwavering. It would carry the heavy size and weight of the turbine in rough sea conditions. Many varieties of foundation systems are available, which can be used based on the depth of a seabed and the geology behind it. Monopile foundations are one of the common options for waters as shallow as 30 meters. Huge steel tubes were driven deep into the seabed. In deeper waters, jacket structures or floating platforms can be utilized. Jacket structures can be envisioned as steel latticework frameworks anchored to the seabed while floating platforms would hold turbines from the ocean surface in place with mooring. The engineers, geotechnical experts, and marine contractors collaborate in designing and installing the most appropriate foundation for the site in question. This stage also covers seabed surveys that identify the nature of the seabed and its adequacy for the foundation type selected.
The latter consists of all the major elements of an offshore wind farm, along with turbines and foundations and an array of electrical infrastructure to transmit the generated power to the onshore grid. It normally comprises inter-array cables that connect the turbines to an offshore substation and export cables that carry the electricity from the substation to the mainland. The offshore substation is very instrumental in stepping up the voltage of the electricity before its transmission onshore. This network, designed by electrical engineers and cable installation experts, shall consider the distance to the shore, water depth, and possible hazards such as fishing activities and shipping routes.
WIND FARM CONSTRUCTION: PROCUREMENT AND MANUFACTURING
The procurement and manufacturing phase involves acquiring all materials and components required for the wind farm construction; this will include the turbines and foundations, electrical infrastructure, cranes, vessels, and specialized tools for installing the wind farm.
The main actors in this stage include wind turbine manufacturers. Offshore wind turbines are manufactured to highly specific sizes and marine environmental demands with component manufacturing expertise from blades to nacelles down to towers. Engineering is so important that a single blade can be up to 100 meters for the biggest offshore turbines. Quality control should be followed at every step of manufacture to ensure that the component concerned meets the required standard for durability and performance. Any defects may lead to costly repairs or efficiency reduction once the turbine is operated.
Transporting the giant components of an offshore wind farm is a logistical headache: turbine blades, towers, and nacelles will have to be moved from the manufacturing plant to a port, from where the installation vessels will load and transfer them to the offshore site. Special vessels, like jack-up ships or crane barges, transport them to the site. Many wind farms are installed far from the coast, and this requires serious work on logistics related to the organization of transport, taking into consideration the weather conditions, port availability, and vessel capacity. Besides this, the installation schedule has to be very tight to enable minimum delay because, in case of interruption of this work, it will result in costly setbacks.
WIND FARM CONSTRUCTION: INSTALLATION AND CONSTRUCTION
Installation and construction at sea is the most complicated and difficult phase in the development process of the offshore wind farm, integrating many different participants in the process: from marine contractors to turbine installers, electrical engineers, and safety specialists.
Installing the turbine foundations is considered the first operation within the offshore construction phase. The vessels used for the operation are basically jack-up vessels or ships capable of jacking themselves above the water by extending legs. The vessel transports the foundation to the site and positions on the seabed. In laying monopile foundations, a very large pile-driving hammer is used to drive the steel tube into the seabed. Noise generated by this process is intense and can harm marine life, particularly marine mammals. To reduce these impacts, noise-reduction technologies like bubble curtains or even quieter pile-driving techniques are sometimes used. Installation of jacket structures or floating foundations is even more challenging and requires multiple vessels along with dedicated equipment. In all instances, very precise positioning is required to ensure the stability and performance of the turbines.
First, the wind turbines can be installed after laying the foundations, which generally consists of transport of the turbine components-tower sections, nacelle, and blades-to the site by installation vessels, subsequent mounting of tower sections at the foundation, and installation of the nacelle and finally the blades. Installation of the blades is especially tricky since each has to be carefully placed and attached to the hub with the use of cranes of an installation vessel. The schedule for installation is badly affected by sea and wind conditions since lifting and positioning blades are prohibited during strong winds or heavy seas for safety reasons. The turbines are to be installed by skilled engineers in this particular field, along with crane operators with expertise in the marine construction field. This shall be done in close coordination to complete the installation without any hurdles and as safely as possible.
Besides the turbines being placed, electrical infrastructure is also installed. Inter-array cables between the turbines are laid, and they connect to the offshore substation. These cables are laid by specialist cable-laying vessels, laying them with care on the seabed and burying them for protection against damage. Afterwards, export cables are laid from the offshore substation to the onshore grid connection point. This may be accomplished by directional drilling that will safely bring the cables through the seabed onto the shore. The cable is laid well by electrical engineers in collaboration with marine contractors, who ensure the electrical connections are secure.
COMmissionING AND TESTING
When all the construction and installation work related to the wind farm is over, the project will reach commissioning and testing. This stage involves a series of tests to ensure that the turbines, electrical systems, and control systems are operating properly and that the wind farm is ready for power generation to begin.
The first test regarding the commissioning process is the commissioning of electrical systems that include inter-array and export cabling, an offshore substation, and the onshore grid connection. The work of electrical engineers involves several tests that ensure the cables are properly connected, and voltage levels are appropriate. Testing is an essential part of this process since any flaws in the electrical system will lead to costly delays. Once all the electrical systems have been tested and approved, it would then be possible to energize the turbines so that they could begin generating power.
Turbine testing involves running each wind turbine through a number of performance tests, which verify that the turbine operates within specified parameters. This will entail observation of the turbine's capability to start and stop, its capability to respond to changes in wind speed, and energy output.
Wind farm operators also study the control systems of the turbines themselves, which act automatically to change the direction that the turbine faces and the speed at which it rotates, both to optimize energy production. Any problems with the turbines or their control systems must also be fixed before the wind farm is operational.
OPERATION AND MAINTENANCE
Once commissioned and fully operational, the wind farm moves into the O&M phase. While designed to require minimal human interaction, offshore wind farms require regular maintenance so that the turbines can continue to function efficiently and safely.
Routine windfarm maintenance includes regular inspections of the turbines, their respective foundations, and electrical infrastructure to inspect wear and tear or any other impending issues. Access is by specialized vessels or helicopters, and routine work in the turbines includes blade cleaning, lubrication of moving parts, and software updating of the control systems. Given the location of most offshore wind farms, maintenance activities must be highly coordinated and planned in great detail. The technicians must consider weather conditions because access to the turbines can be unsafe if there are rough seas or very high winds. (see also: walk-to-work offshore)
Aside from routine maintenance, unplanned maintenance may be required if a fault or some kind of mechanical failure occurs in the turbines. Such events are expensive, especially when major vessels and cranes are required to replace or repair a defective component. In many instances, one turbine being out of commission could mean the wind farm will lose potential revenue due to lost energy. Since this greatly reduces the likelihood of unplanned maintenance, many operators of wind farms have applied remote monitoring systems that track the performance of each turbine continuously. In this respect, providing early warnings of developing problems enables technicians to effect repairs before the problems worsen.
Uncertainties and Hazards in Offshore Wind Farm Construction
While the construction process of offshore wind farms has been somewhat standardized during the last years, there is still a long list of uncertainties and hazards that may influence the completion of a project.
The weather conditions are the biggest uncertainties in the construction of offshore wind farms. Storms, high winds, and rough seas can lead to postponed installation activities and probably losses of equipment. This sometimes can go as far as hurricanes or typhoons that, in turn, destroy an offshore wind farm, thereby resulting in very costly repairs and a waste of time, or sometimes not being possible at all. This risk is minimized due to the use of detailed weather forecasting and planning tools by the project planners, who carefully find the best window for the installation. However, there is always going to be a problem with unpredictable weather.
In addition, the construction of offshore wind farms may be affected by environmental and regulatory uncertainties. Changes in environmental regulations, objections from local communities, or court suits on environmental impact could result in project delays or cancellations. Another risk that exists during the EIA process is unexpected discoveries; for instance, sites hosting protected species necessitate expensive modifications in the design or relocation of a site. To manage these risks, the developers of projects will be obligated to seek out, early in the planning process, the involvement of regulatory bodies, environmental groups, and local stakeholders in consensus building to meet all applicable regulations and requirements.
The only way this can be achieved is by manufacturing and transporting turbine parts, vessels, and a variety of other speciality equipment on a highly complex global supply chain. Delays in the supply chain-through factory delays, shortages in labour, or bottlenecks in transport-can really set back project schedules. Developers of wind farms, therefore, will tend to seek out multiple sources of major components and incorporate contingency into their transportation logistics to avoid risks in supply chains where possible.
The development and maintenance of wind farms offshore is a very hazardous process. Laying out turbines and electrical systems at sea is already a very dangerous thing to do, with the fury and power of the sea. Technicians and construction workers, among others, have to deal with risks of falls, equipment failure, and extreme weather conditions. To avoid all such perils, strict safety policies have been adopted in every stage of construction and operation. The workers are highly trained, and special safety equipment, such as harnesses and life jackets, are employed in order to reduce such risks. Other measures include safety drills and an emergency response plan to ensure the employees act effectively in case of an accident.
FAQ
What are the main phases of offshore wind farm construction?
Offshore wind farm construction follows six main phases. First is the feasibility study and site selection, which involves assessing wind resources and environmental impacts to identify a suitable location. Next is the design and engineering phase, where detailed plans for turbines, foundations, and electrical systems are developed. Components are sourced and prepared for installation in the procurement and manufacturing phases. The construction and installation phase follows, where turbines and infrastructure are set up at sea using specialized vessels. Once built, the commissioning and testing phase ensures all systems function properly before the farm becomes operational. Finally, during the operation and maintenance phase, routine inspections and repairs are conducted to keep the wind farm running efficiently.
What are the biggest risks and uncertainties in offshore wind farm construction?
Key risks include unpredictable weather, such as storms and rough seas, which can delay construction and increase costs. Environmental and regulatory challenges, such as legal disputes or unexpected findings during assessments, can also cause delays. Supply chain disruptions, like manufacturing or transportation issues, pose another risk. Safety hazards due to the harsh marine environment also present significant concerns during construction and maintenance.
TAKEAWAY
The construction of an offshore wind farm is a very complex, multi-disciplinary task, extending from project developers and manufacturers to ecological consultants to controlling bodies. Each stage- from feasibility studies to design, construction, and operation- comes with various challenges, uncertainties, and hazards.
In spite of the above complexities, offshore wind energy is growing as an important part of the world's transition to renewable energy. By harnessing the continuous and strong winds at sea, large-scale supplies of clean, sustainable electricity could be gained from offshore wind farms. As technology advances and experience is gained within the industry, the obstacles regarding constructing an offshore wind farm will, without question, become easier to deal with, offering additional prospects in the future.
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Sources:
(1) https://www.polandatsea.com/step-by-step-how-the-construction-of-an-offshore-wind-farm-proceeds/
(2) https://windenergyireland.com/images/files/iwea-onshore-wind-farm-report.pdf
Author
Michal Wozniakowski-Zehenter, Marketing Manager
Michal Wozniakowski-Zehenter is an experienced marketing and project management professional. He spent most of his career on projects with a strong focus on digital marketing and event management. He is a very active voice representing offshore and mining industries through social media channels. Michal writes mainly about offshore oil and gas, renewable energy, mining and tunnelling. Compiling and sharing the knowledge within industries is one of his goals.
