Nick Murphy is the commercial manager for OpenHydro, Dublin, Ireland, which manufactures and installs tidal energy-generation systems. The company’s next major project is to deploy an array of 13 feet x 52.5 feet open-centre turbines in the Paimpol-Bréhat (Côtes d’Armor) region of Brittany, off the coast of France. This will be the first project featuring OpenHydro’s 52.5-meter turbine. The first unit is scheduled to be installed this summer, with the remaining turbines installed in 2012. Snohomish Public Utility District, in Snohomish, Wash., is engaged in an OpenHydro composite tidal turbine demonstration project, in the challenging, yet potentially robust testing site in Puget Sound’s Admiralty Inlet.

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What composite materials are used in the OpenHydro turbine?

OpenHydro is first company to complete the connection of an embedded tidal turbine generator to an electricity distribution network in the UK. This challenging undertaking followed a complicated project to relay 1,600 feet of subsea cable and terminate it to the research structure, as well as developing and installing a grid compliant power conversion system on the structure. As you can imagine, this was a large undertaking. A large percentage of the turbine material is glass fiber-reinforced plastic (FRP) which we found works very well in the applications. This includes the blades, which are wholly constructed from FRP. In terms of the primary structure, we used FRP as well as some steel (both mild and stainless.) The “active” components within the generator include generator copper coils and wiring and neodymium permanent magnets.

What challenges arose in the engineering of this technology?

The open-centre turbine is designed to operate in a harsh marine environment and under extremely high tidal loading. It is designed from first principles for the marine environment and does not represent a marine-ized version of an equivalent onshore technology type. The turbine uses an inherently simple permanent magnet generator design, which incorporates a single moving part with no gearbox or other complicated components that would require regular maintenance or pose a significant failure risk.

What future do you see for this technology?

It’s our belief that if a turbine is to not only survive but also to operate effectively in the marine environment, it is essential that the unit be both simple and robust. We believe this is a viable technology with the potential to generate predictable, renewable energy from the tides at an economic price. It has also challenged us to develop new and innovative solutions to such challenging problems as the deployment and recovery of our turbines, whilst keeping the costs within acceptable levels.

What have you learned so far at this stage of the game?

We recognize that there are four distinct and essential elements required for the commercial production of electricity from tidal energy:

  • Tidal turbine: a proven and robust turbine technology to convert the movement of water into electricity;
  • Deployment system: a safe and cost-effective method to install the turbine and recover it for routine maintenance;
  • Electrical connection: the technology to connect, convert and export the power onto a national grid;
  • Maintenance: an efficient and cost-effective approach for ongoing maintenance of tidal arrays.

Why did you choose to use composites?

Composite materials are well proven in the marine environment. They have a high strength-to-weight ratio and good fatigue life properties.

Did you have any difficulties implementing the different materials together?

Initially yes, but through six years of research, development and testing, including a European Marine Energy Centre (EMEC) research structure (completed November 2006); a grid connection of the EMEC Research Structure (completed May 2008); design and fabrication of the OpenHydro Installer, and EMEC subsea base deployment (completed September 2008); and, in the Bay of Fundy, a deployment (completed November 2009), and a Recovery Operation (completed December 2010). We have overcome these and now have working solutions. We continue to do R&D in this area to improve efficiencies and to reduce cost.

What more would you like to see in developments in composites technology that could be useful to utilizing tidal power for energy generation?

As with any material selection we always seek the strongest, lightest material with the best through-life properties for the least cost. Specifically, developments in techniques for bonding components once manufactured would be useful.