Planning a Marine Energy Project: Cable Considerations

Whether marine energy project planners deploy wind, wave or tidal devices, they cannot afford to overlook the basics: transmitting power back to the mainland via electrical cables.

There’s an abundant body of knowledge on transmitting electrical power via underwater cables because power companies have been doing it decades. Indeed, Europe’s mature offshore wind industry has amassed considerable working knowledge on the most common challenges of subsea electrical cables.

Here’s a concise overview of them:

Installation and Positioning

Power cables for marine energy projects most likely will be installed with cable-laying machines that bury them at a specific depth below the sea floor. This is mature technology; the main challenges are straightforward: working around the weather and hiring a ship to lay the cables.

The greater challenges come from determining exactly where the cables will go. A host of position-related questions crop up:

• Are any other cables or utility pipelines already installed nearby?
• What’s the regulatory status of the installation site — is it a protected ecosystem?
• What’s the seabed terrain like?
• How stormy is the local weather?
• How far apart should cables be placed?
• How much shipping, fishing and other commercial activities happen nearby?

An in-depth review by the U.S. Department of the Interior’s Bureau of Safety and Environmental Enforcement noted that there so many variables with cable installation that project specifics will have to be decided on a case-by-case basis.

Protection

Cables must be built to withstand the rigors of the subsea environment. Furthermore, any cable accessories that connect various cable parts have to be extremely rugged and seaworthy, providing reliable cable protection, terminations and splicing. Project planners need to invest time in researching accessories that strengthen and protect cables, making them less vulnerable to corrosion, currents and other subsea threats.

Mooring

Depending on the location, some cables require mooring lines to hold them in place. These lines may require anchors embedded in the sea floor. Once the cables are moored, the lines may attract aquatic species that start building artificial reefs; this may trigger environmental questions.

Maintenance and Repair

The ocean environment does not cooperate with the need to maintain and repair subsea cables. Ship anchors and fishing nets may snag your power lines, and inconvenient storms can keep repair crews away for weeks or months. Even in the best weather, it can be extremely difficult to identify precisely where a cable is damaged.

Fortunately, technology is getting much better at predicting when parts will fail so replacements can be installed on schedule rather than in a chaotic emergency-repair scenario.

Monitoring

A power grid buried beneath the sea floor requires constant surveillance — the environment creates so many challenges and risks that it’s extremely difficult to anticipate all the ways things can go wrong. Advances in monitoring technology will help narrow down the source of a problem when it crops up, but it’s still a matter of fixing things buried under seawater. That’s always a challenge.

Addressing the complexities of subsea cable grids

All these points illustrate the need for a well-planned, well-executed marine energy project that anticipates the many challenges that crop up when devices and equipment get placed in a saltwater environment.

At PMI, we pay a lot of attention to making sure splices, terminations, cable protection and other accessories do not become weak links in a subsea power grid. With all the risks in the subsea environment, investing in the best cable accessories can mean one less worry for marine energy project planners.

Related articles:

• Subsea Cable Trade Group Widens Focus to All of Europe
• Offshore Wind Farms Still Learning How to Handle Cables
• What kind of ocean equipment will be needed for subsea power grids?