How Does Offshore Wind Power Work?
Offshore wind power is a form of renewable energy that generates electricity using large wind turbines placed out at sea, typically in the open ocean. It provides an alternative source of clean electricity compared to the traditional power plants that run on fossil fuels. This article will provide an overview of how offshore wind power works – covering the key components like wind turbines and foundations, installation, operation and maintenance, as well as environmental impacts and future outlook for this fast-growing industry.
Wind Turbines
Offshore wind turbines consist of several key components that allow them to capture energy from the wind and convert it into electricity. The main parts include:
The rotor blades which capture the wind energy. Most offshore turbines have three blades made of composite materials like fiberglass. Longer blades can capture more wind.[1]
The nacelle which sits atop the tower and contains components like the main axle, gearbox, generator, transformer, and control systems.[2]
The tower which supports the nacelle and allows access to the nacelle. Offshore wind turbines use tubular steel towers anchored to the seabed.
The foundation which anchors the turbine tower to the seafloor. Common offshore foundations include monopiles, jackets/tripods, and floating platforms.
As wind blows across the blades, the rotor spins. This rotational energy gets converted inside the nacelle into electrical energy using electromagnets and gearboxes. The electricity then gets transmitted via undersea cables to the onshore grid.
Foundations
Offshore wind turbines require specialized foundations to anchor them to the seafloor. There are several main types of foundations used for offshore wind turbines:
- Monopile foundations – These consist of a single steel pile driven deep into the seabed. They are the most common foundation used in offshore wind farms today due to their simple design and ease of installation in shallow waters up to around 40 meters deep (1).
- Jacket foundations – These lattice-type foundations consist of a jacket structure anchored to the seabed using piles. They are suitable for deeper waters over 40 meters and are more complex and expensive than monopiles (2).
- Floating foundations – These foundations allow wind turbines to float while anchored to the seabed by mooring lines. They are emerging for use in very deep waters over 60 meters where seabed foundations are not feasible (1).
- Gravity base foundations – These large concrete structures rely on their weight to remain stable on the seabed. They are less common today but were used on some early offshore wind farms (2).
- Suction bucket foundations – These are essentially large inverted buckets embedded into the seabed by pumping water out. They are newer designs still in development (1).
The choice of foundation depends on factors like water depth, seabed conditions, turbine size, and costs. But monopile and jacket designs remain the most prevalent types used in offshore wind farms today.
(1) https://www.iberdrola.com/sustainability/offshore-wind-turbines-foundations
(2) https://www.windpowerengineering.com/comparing-offshore-wind-turbine-foundations/
Location
The ideal locations for offshore wind farms are areas that have strong, steady winds, shallow waters, and proximity to major population centers that require electricity. Some of the best offshore wind resources in the United States are found along the Atlantic coast, the Gulf coast, the Great Lakes, and Hawaii (NOAA).
In particular, the outer continental shelf off the coasts of New England and the mid-Atlantic states has excellent wind speeds for generating energy. Shallow waters off the coasts make installing turbine foundations more feasible. And the proximity to major coastal cities like Boston, New York, and Washington D.C. means the electricity generated can be transmitted directly to where it’s needed (Offshore Wind Maryland).
Other prime locations for offshore wind farms include the Great Lakes, especially Lake Erie and Lake Michigan where wind speeds are strong. And the islands of Hawaii also have ideal wind conditions and high electricity costs that offshore wind could help reduce.
Installation
Installing offshore wind turbines is a complex process that requires specialized equipment and vessels. The most commonly used vessel is called a jack-up rig, which has extendable legs it can lower to the seafloor to lift the hull out of the water and create a stable platform for crane operations.
First, the tower sections, nacelle, and blades are transported to the installation site by a transport vessel or barge. The components are then lifted and assembled piece-by-piece by the crane on the jack-up rig (1). The tower sections are lifted one at a time and bolted together to form the full tower. Next, the nacelle containing the gearbox, generator, and other machinery is hoisted to the top of the tower and attached. Finally, the blades are individually lifted and secured to the rotor hub on the front of the nacelle (2).
Once fully assembled, the completed turbine is then lifted as a single unit by the jack-up rig’s crane and positioned over the prepared foundation. It is slowly lowered into place and attached via a transition piece that connects the tower to the foundation (3). The turbines are spaced apart in a planned array to minimize wake effects from upwind turbines. Electrical cables are laid along the seafloor to connect strings of turbines back to an offshore substation platform.
Transporting and installing the massive components far offshore requires calm seas, precise execution, and close coordination between vessels. But with specialized jack-up rigs and an experienced marine construction crew, offshore turbines can be assembled and deployed efficiently.
Sources:
(1) https://www.onesteppower.com/post/how-are-offshore-wind-turbines-installed
Operation
Offshore wind turbines operate on a simple principle to generate electricity. When the wind blows, the blades of the turbine spin around. The turbine has a shaft connected to the blades and a generator inside. As the blades spin, the shaft turns, which makes the generator spin. The spinning generator produces electricity through electromagnetic induction.
The electricity generated by each individual wind turbine is transported via cables inside the turbine tower to a transformer station on the wind farm. The transformers step up the electricity to a higher voltage so it can be efficiently transmitted long distances. From the offshore transformer station, submarine cables transmit the electricity to an onshore substation, where it is connected to the main transmission grid.
Modern offshore wind farms have remote monitoring and control systems. This allows operators onshore to monitor the turbines and optimally adjust their operations for maximum power generation. Sophisticated control systems can feather the blades to protect components in high winds and even shut down turbines if needed.
Offshore wind turbines are highly automated and designed to operate unmanned. But regular maintenance is still required to keep them functioning properly. Technicians travel to the turbines by boat or helicopter to perform routine inspections and any needed repairs.
Maintenance
Maintaining offshore wind turbines presents unique challenges compared to land-based wind turbines due to the marine environment. Routine maintenance on offshore turbines is difficult because they are located far from shore and are only accessible by boat, which is dependent on favorable weather and sea conditions (ScienceDirect). Maintenance teams are limited on the time they can spend on each turbine due to the logistics of traveling far offshore. Components are also subjected to corrosion from the salty sea air and must be built to withstand ocean storms (GE).
According to GE, maintenance on offshore wind turbines includes inspecting components and systems to identify signs of wear and tear. Teams perform preventative maintenance like lubricating parts, tightening bolts, and replacing worn components. Major overhauls are done periodically to conduct more significant repairs. Monitoring systems track performance and can identify problems early. New remote monitoring and control systems allow some basic maintenance to be done remotely without sending teams offshore.
Environmental Impact
Offshore wind farms can have both positive and negative impacts on the marine environment. On the positive side, the underwater structures of wind turbines can act as artificial reefs, providing surfaces for algae and invertebrates to grow and offering shelter for fish. This can increase local biodiversity and biological productivity (https://www.umces.edu/wind-energy). Some studies have shown offshore wind farms have a “reef effect” leading to greater species richness and abundance of marine organisms compared to the surrounding seabed (https://www.nature.com/articles/s44183-022-00003-5).
However, there are also some concerns about the negative environmental effects of offshore wind farms. The construction process can disturb and resuspend contaminated sediments, increase noise and vessel traffic, and disrupt habitats and species. The physical presence of turbines may alter currents and waves, potentially changing sediment transport and habitat. Underwater noise, electric and magnetic fields from cables, and lights may impact marine mammal and fish behavior. And birds and bats can collide with turbines leading to injury or mortality.
Overall, research shows mixed results on the net environmental impact. With proper siting and mitigation strategies, offshore wind’s benefits could outweigh the costs. But more long-term monitoring is needed, especially as larger scale projects are developed farther offshore.
Costs
The costs of offshore wind power have been rising steadily in recent years. According to BloombergNEF, the levelized cost of electricity from a subsidized US offshore wind project has increased to $114.20 per megawatt-hour in 2023, up almost 50% from 2020. Supply chain disruptions, inflation, and rising commodity prices are major factors behind these increasing costs.
Offshore wind turbines themselves are expensive, with costs estimated between $4-6 million per megawatt of capacity. Larger 12 MW turbines can cost up to $400 million to manufacture and install according to Today’s Homeowner. Foundations, subsea cables, and other infrastructure add substantially to costs as well. Transporting and installing turbines far offshore is complex and expensive.
Despite rising short-term costs, analysts expect longer term cost reductions as the offshore wind supply chain matures and larger turbines reap economies of scale. But cost overruns could impact project viability and deter future investment if costs are not reined in. Overall, offshore wind remains more expensive than onshore wind and solar power currently. Ongoing innovation and increasing deployment will be key to reducing offshore wind costs over time.
Future Outlook
The future looks bright for offshore wind power. According to the U.S. Department of Energy, the Biden administration has set a goal to deploy 30,000 megawatts (MW) of offshore wind energy by 2030, which would power 10 million homes with clean energy.[1] Europe currently leads in offshore wind capacity, but growth in the U.S. is expected to accelerate in the coming years.
There are several growth drivers that make the outlook positive for offshore wind. First, costs have fallen dramatically in recent years making offshore wind competitive with other energy sources. Second, floating turbine technology is unlocking new areas for development further from shore and in deeper waters. Major projects using floating turbines are already underway. [2]
Innovations on the horizon include larger and more efficient turbines, improvements in operations and maintenance, high voltage direct current transmission, and advancements in floating foundations. With strong policy support, falling costs, and major offshore wind lease areas already auctioned, the U.S. offshore wind industry is poised for robust growth in the years ahead.
