Deep-sea shuffle

Unlike other systems, the weather-hardy C-Wave device uses waves’ sideways movements to generate electricity

A low-cost wave energy technology is being developed that uses the unique hydrodynamics of waves and will be able to survive even the most hostile of ocean conditions. The system is also claimed to be far more efficient than other, similar systems in converting waves into electricity.

The principle upon which the C-Wave device, made by the company of the same name, operates is deceptively simple and sets it apart from other spin-out wave energy devices, such as the Manchester Bobber (The Engineer, 19 September 2005). While the Bobber uses the up-and-down motion of the waves to drive a generator, the C-Wave uses the distance between waves to the same effect.

The new company is based at Southampton University and tests its systems in the university’s wave tank. However, it is an independent business with no formal academic ties.

According to Giles Edwards, C-Wave’s chief executive, the device makes use of the same properties of waves that make it difficult to jump from one boat to another while at sea.

‘A wave does not just move up and down,’ said Edwards. ‘When it moves past it doesn’t mean that a lot of water is passing by at the same time. The water actually moves around in a circle, so as well as an up-and-down motion you also get a side-to-side movement. This is why, when you put two objects next to each other in the sea, the gap between them will continually open and close because they are in different wave phases.’

The system uses this phase movement by installing a generator device between two movable walls and harnessing that back-and-forth motion to generate power. Between the three moving walls, piston-like hydraulic pumps convert the horizontal movement into hydraulic pressure which, in turn, powers the generators. These, along with a host of power-conditioning technology, are stored in the device’s walls — where they are kept watertight — and produce power that can be linked straight to the power grid via sub-sea power cables.

Edwards claimed the C-Wave design has a number of advantages over its wave-power rivals. He said most wave-energy designs operate on principals of buoyancy and are either pushed up and down — like the Bobber — as they work against themselves or the seabed to produce power.

‘Most wave-energy devices don’t actually gather that much energy from each wave,’ he said. ‘We absorb a huge amount, meaning that because our mechanism absorbs more power per unit our capital costs are lower.’

The system’s other advantage is its durability, he said. The C-Wave will be tethered loosely to the ocean floor in much the same way as a ship, so the strains produced on devices that are tethered more firmly will not be a problem during a storm, he claimed.

The system is also designed to be long- lasting, with a planned 20-year lifespan. The first prototype will be made from steel, but Edwards envisages future systems could be constructed from concrete.

Each huge device, up to 75m long x 30m wide, would be capable of producing about 2MW initially, claimed Edwards, with the first wave farms consisting of about 10-20 connected devices located up to 20km offshore.

So far C-Wave has raised nearly £1m to fund its initial development programme. For the next phase it hopes to raise a further £5m-7m over the course of 2007 to produce and install a full-scale, 1-2MW prototype system in the Atlantic off the Orkney coast.

In the first quarter of 2007 the company will finish validating the system’s engineering feasibility and the hydrodynamics of the system before moving into the prototyping stage, developing intermediate scale devices that it will test in the university’s wave tanks, said Edwards.