Making the Right Connections for Wave Energy Installations

Despite the global pandemic, wave and tidal energy projects have moved forward at pace, reaching significant funding, testing and deployment milestones over the last year.

One such example is Acteon’s patented Rocksteady connection system, an auto-latching subsea structural connector that enables wave energy operators to streamline installation processes and minimize costs.

Wave energy projects are, by their nature, located in challenging environments where installation operations must contend with rough seas and high winds. In these conditions, it is not feasible to install traditional pin-and-shackle connectors. Wave energy operators need simple, cost-effective systems that enable installation in rough conditions and can withstand the demands of the environment.

The Rocksteady connection system is designed to meet that challenge.

ROCKSTEADY DESIGN

Experience in testing and offshore deployment show that the Rocksteady connector enables high-speed latching (3 m/s) with a high angle tolerance (up to 25°) and that it will connect and release in all weather conditions. This means wider installation windows and far shorter installation times, reducing the expense and environmental footprint of offshore vessels.

Though smaller and lighter than other subsea mooring connectors, Rocksteady has full ABS and DNV qualifications. The system has been designed for and break-load, fatigue and durability tested to qualify capacities of up to 3,000-t minimum breaking load.

The Rocksteady locking mechanism was inspired by the wellhead collet connectors used in the oil and gas industry. It transfers the load to forged load shoulders to give excellent fatigue performance and, with a preloaded option (Gen-1), the unique ability to accommodate different types of load. This is important because, unlike traditional moorings where tension is the main consideration, wave energy connectors must also deal with bending, compression, shear and torsional forces. The preloaded option also overcomes the major issue of fatigue from these combined loads.

The combined loading capability also greatly simplifies offshore installation, as the Rocksteady connector can lock directly into a seabed foundation, such as a gravity base or pile, with a bearing unit integrated above the connector. This overcomes the need to install bearings on the foundation; these must be supported vertically during pull-in and installation, then released for operation, often an expensive and time-consuming diver or ROV operation.

In subsea applications, reliability is crucial. The Rocksteady locking mechanism is simple and all its moving parts are recoverable. The load path components are fully forged and have field-proven coatings and seals to protect the internal components from corrosion and debris.

BUILT ON EXPERIENCE

Even though the Rocksteady connection technology was developed with the oil and gas industry in mind, its initial deployment was for the Perth Wave Power Project, a demonstration system offshore Western Australia on behalf of Carnegie Clean Energy. In that first application, the Rocksteady system significantly reduced the installation time and the amount of diver intervention needed to complete the project. Since then, there have been numerous refinements and three new generations of the product.

Rocksteady connectors are manufactured by Acteon. Having all aspects of the process in-house, from design drawings, specifications and procedures through to manufacture, assembly and system testing, simplifies the procurement process for operators, minimizes lead times and ensures that the product meets project specifications. However, for customers that want direct control, there is an option for operators to manufacture under license, which may also help them to meet local content requirements.

TAILORED SOLUTIONS

Recently, Rocksteady connectors were selected for use on wave energy demonstration projects offshore Portugal and Scotland (UK), both of which will install devices in 2021.

A key challenge in wave energy projects is making the electrical connection that takes power from the device to the grid and the data connection that enables the operators to control the device. Using the Rocksteady connection system, it is possible to make these connections at the same time as the mooring connection. This approach also enables same-time installation of structural integrity monitoring systems, if required.

CorPower Ocean (www.corpowerocean.com) has ordered a Gen-1 Rocksteady connector for a new wave energy converter (WEC) project where integration and deployment efficiency are key requirements. The Rocksteady connector will be deployed on a full-size demonstrator project that will generate power primarily from the heave motion of four buoys. The HiWave-5 project, located in Aguçadoura, Portugal, will be conducted in a 44-m water depth, with each of the buoys having a 300-kW rating.

The plan for this project is to make the electrical and data connections simultaneously using the Rocksteady’s pull-in, capture, rotational alignment and latching features. Rocksteady connector control functions and sensors have been tied into CorPower’s WEC control system and a bearing unit integrated with the retrievable connector and WEC assembly. This approach will dramatically shorten and simplify the installation process.

Avoiding the need for separate bearing installation, power and data hookups will reduce the project footprint, lower environmental impacts and offer substantial savings by minimizing vessel and subsea intervention costs.

The AWS Ocean Energy Ltd (www.awsocean.com) Archimedes Waveswing is a submerged wave power buoy that reacts to changes in water pressure caused by passing waves and converts the resulting motion to electricity via a direct-drive generator. The first marine deployment will use a Rocksteady connector on a half-scale demonstrator unit to be installed at the European Marine Energy Centre in Scotland, UK.

The order for a Gen-4 connector was placed in December 2020. The product was tested in March 2021 and delivered in April and is scheduled for installation over the summer. The Gen-4 Rocksteady device is relatively simple and has a stripped-down design that enables mechanical connection and disconnection from the surface, either from a connected line or mooring line chaser. This makes it a cost-effective and priced-for-commodity system that can be easily scaled up from demonstration units to large commercial projects.

THE FUTURE

The wave energy sector is in an important transition phase, during which some wave energy converter (WEC) technologies will be scaled up for full commercial operation. This presents a range of challenges, including finding efficiencies and controlling costs as the average project size increases; minimizing the environmental impact of installation projects by optimizing vessel usage; and finding ways to drive down the costs of installation in deeper water and more demanding environments.

At Acteon, we aim to help operators meet these challenges and build a marine green energy future.

For more information contact info@acteon.com or visit www.acteon.com.

This story was originally featured in ON&T May 2021. Click here to read more.