Professional Engineering

While it’s often said that Britain will become a world leader in marine energy, it is actions rather than words that will result in the commercial exploitation of the bountiful tides and waves around our shores.

To that end, there are dozens of small engineering-led companies that are designing and building prototype devices to put into the water. Marine energy might have huge potential, but it is only through the endeavours of such pioneering organisations that the promise will ever come to fruition.

Cardiff-based Tidal Energy Ltd (TEL) is a good example of a renewable energy firm that is moving steadily towards commercialisation of a promising device. TEL has been working for more than 10 years on the refinement of its DeltaStream tidal converter, which it hopes to test next May in the Ramsey Sound off the coast of west Wales. It has been a long journey so far, and there are still challenges to be overcome.

“Essentially, there have been three broad areas that have needed to be addressed to enable us to progress to where we are: access to finance, the design of the device, and marine conservation,” says Martin Murphy, TEL’s managing director. “We are now at a stage where we are planning to install a utility-scale DeltaStream prototype in Ramsey Sound next year. We’ve come a long way over quite a long period of time.”

Finance is a perpetual struggle for marine energy firms. There are pockets of cash available from organisations such as the Carbon Trust and the European Regional Development Fund but grants often have to be matched by private capital. TEL was fortunate: in 2007 it secured major backing from Eco2, a much larger renewable energy company that specialises in biomass and wind. This deal gave TEL the funding it needed to get where it is today. Without it, says Murphy, progress would have been far slower.

The technological challenge of designing a device that can operate reliably has also tested Murphy and his team. TEL has tried to keep things simple: its concept of a horizontal-axis turbine is quite straightforward, but its development has still required an enormous amount of consideration. “We will be putting the device into a very harsh environment where vast quantities of water will be moving very quickly. It’s not an ideal place to put something that you want to stay put and generate energy. The challenges associated with that are very considerable,” says Murphy.

And then there is environmental assessment. Potentially, the DeltaStream device could cause damage to marine species, the seabed and to water quality. “Ramsey Sound is an area of marine conservation,” he says. “We have had to be careful when progressing the design to be sensitive to the environmental conditions. We have had to work with environmental regulators in seeking licences and consents to put the design in the water. And when the turbines are operating there will need to be careful environmental monitoring.”

The DeltaStream tidal converter is a lightweight gravity-based design with relatively slow rotational speed. Each device will have three tidal-stream turbines, made up of a nacelle, hub and blades. DeltraStream features fixed-pitch blades and a yaw mechanism, rather than a controllable pitch system, to drive the nacelle around from one direction to another to face the oncoming tidal flow. 

When the rotors are turned by the tidal flow, the combined generation capacity of the three turbines will be up to 1.2MW.

Murphy says the triangular design stems from a belief that multiple turbines on a single structure is the best way to move forward. “The energy generated is directly proportional to the swept area of the turbine. So the greater we can make the swept area for a given device, the greater the average energy output will be. 

“We’ve been through a whole series of iterations to try and optimise where we think the design should be.”