With President Joe Biden setting a 30-GW offshore wind goal by 2030 for the United States, the industry is ready to take off. This massive development is a very ambitious goal that will require detailed engineering and planning. One thing that shouldn’t be overlooked is the cabling needed to get this wind energy to shore and into communities.
Offshore wind from the ground up
Offshore wind turbines require thousands of kilograms of precious materials, including copper, nickel, manganese, chromium, zinc and more. Beyond the turbines, offshore wind farms require high-voltage cables to connect to the grid. These cables will require even more precious materials that need to be mined.
Currently, there is a huge global demand for these cables as well as limited production capacity — and as the offshore wind industry grows, so too will the demand for cables. That means procuring cables will take longer than usual. It’s critical to engage cable manufacturers as early as possible in the project’s life cycle.
Siting and connecting offshore wind farms
Offshore wind farms currently being proposed in the United States are mostly located approximately 15 to 30 miles from shore. This distance will increase as the industry grows and more turbines are needed further offshore. The size of these offshore wind farms will grow too — both in terms of the number of turbines and the generating capacity of each turbine. Further developments in turbine generating capacity will drive the industry to higher capacity farms, especially in locations farther from shore. Both floating and fixed offshore wind farms are turning to high-voltage direct-current (HVDC) transmission lines as projects move further away from the shore.
Routing offshore wind cables
It’s essential to find the right route for transmission cables. It would be optimal to route the cables from the offshore wind farms directly to the shoreline and immediately connect into the electrical grid at the closest substation. But this is not always possible due to constraints in the water, such as marine-protected areas, underwater canyons and high shipping traffic areas. We also must consider the design of the onshore electrical transmission system. It may not be ready to accept offshore wind power at shore locations that are already congested.
The points of interconnection in the electrical system need to be determined by conducting power system studies. Having knowledge of the electrical system is important, as transmission capacity may be available in the future where there are non-renewable generating plants planned for retirement. In many areas, the electrical system close to the coastline is not sufficient to carry large amounts of power from the offshore wind farms further into the grid. These instances require additional onshore transmission upgrades. This calls for coordination with the local planning authority and the utility that owns the substation where the connection is being made.
Landfall locations for the cables need to be selected carefully. It’s important to consider environmental constraints, coastal protection requirements and construction requirements. Generally, horizontal directional drilling is used to install the cable from a location a few hundred meters off the coast. This allows contractors to bypass — and not disturb — the shoreline.
Protecting offshore wind cables
Another thing to consider is finding an effective way to protect the cables. According to reports from insurers, approximately three-quarters of all offshore wind insurance claims are related to cables. And 88% of those cable-insurance claims are related to the export cables, which transport the power to shore. Damaged cables can be very costly to repair — it’s not only the cost of the cables, but the cost of the outage.
Mechanically protecting submarine cables can assist with reducing damage from anchors, fishing gear, dredging and more. This requires a detailed geophysical and geotechnical surveying of the cable route, along with a cable burial risk analysis.
The submarine cable route may also need to cross over other linear infrastructure assets such as communications cables, other power cables or pipelines. In these instances, it is important to engage with the asset owners as early as possible to develop cable crossing requirements and agreements.
A lot of work goes into protecting transmission cables. Having a repair preparedness strategy in place can help to minimize the outage time if damage occurs. Those strategies ensure that all documentation, permits and framework contracts are in place for all aspects associated with cable system repair.
Mitigating impacts to the surrounding environment
While it is critical to protect the cables, it’s also important to minimize impacts to the environment. The primary environmental concerns with offshore wind transmission are the impact to the seafloor, sensitive coastal environments and other marine life. There is also concern with potential conflict with other ocean uses.
Installing cables can create a temporary disturbance of the seabed and may transverse through sensitive environments. Benthic resources are documented, and the impacts must be minimized through the permitting process for construction. The same is true for other methods such as dredging in high relief areas or protecting surface laid cables.
Offshore wind projects also must consider avoiding sensitive habitats wherever possible. This is where horizontal directional drilling at the ocean/land interface comes into play. This helps avoid sensitive shoreline resources and habitats by drilling at depths below them.
Cable installation must also account for other ocean uses such as fishing interests, sand borrow areas, artificial reefs and navigation channels. Burial must be at sufficient depth in or around these areas to avoid direct contact and potential impacts.
Offshore wind power into our energy grid
Once the cables reach shore, there is a need for more infrastructure and more cables to transmit the power, either underground or overhead, to the designated substation. Both transmission cable options can have an impact on the environment and must be addressed. Public outreach is important. The electrical substations and equipment needed to tie into the points of interconnection will require more land. Ideally, the point of interconnection is as close as possible to the submarine cable landing point.
Cables are an important part of offshore wind, and having an upfront knowledge about the challenges developers may face will assist in successfully delivering bountiful offshore wind energy into our communities.
Ralph Kurth is Senior Principal, Energy, for Stantec. With more than 35 years of experience, Ralph has worked on a range of power system projects. His focus is currently on HVDC transmission systems, AC substations and their automation systems. While his assignments are wide ranging and complex, his goal remains the same — to provide solid advice to project teams and clients.
John Crowther is Senior Principal, Environmental Services, for Stantec. John has over 35 years of environmental consulting experience. A geologist by education and training, John applies his diversified experience in the geologic and physical environment as well as the marine ecological environment. John brings together Stantec’s environmental services and power engineering groups to deliver integrated solutions to Stantec’s offshore wind clients.
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