The next wave of energy from the sea

A recent study by the Carbon Trust predicts that by 2050 wave energy could yield as much as 190 gigawatts of electricity or more than 3 times today’s total electric output in the UK. As the industry begins to scale up, more than…

A recent study by the Carbon Trust predicts that by 2050 wave energy could yield as much as 190 gigawatts of electricity or more than 3 times today’s total electric output in the UK. As the industry begins to scale up, more than 100 companies are developing novel devices to harvest energy from the seas. New Scientist takes a look at some of the most promising technologies currently being deployed.

The Point Absorber

Sometimes the simplest designs are the best. The point absorber is a floating buoy that rises and falls with each passing wave, converting mechanical motion into electricity. As the buoy heaves up and down the movement is used to pump hydraulic fluid in a fixed cylinder that lies beneath the surface. The pressurised fluid spins a generator within the device, creating electricity that is transferred to shore via underwater transmission lines.Ocean Power Technologies of Pennington, New Jersey is currently testing its PowerBuoy – which measures 41 metres tall and 11 metres in diameter – in Scotland. It is expected to produce 150 kilowatts of continuous power.

The Attenuator

Attenuators are long floating devices that run perpendicular to oncoming waves and harvest energy from tip to tail. As waves pass along the length of the machine, individual sections heave up and down relative to each other creating mechanical movement that is converted into electricity. Pelamis Wave Power of Edinburgh, UK is currently testing its second-generation commercial-scale attenuator at theEuropean Marine Energy Centre off Scotland’s Orkney Islands. The device, known as P2, is 180 metres long, 4 metres in diameter, and produces 750 kW of electricity.

Oscillating Wave Surge Converter

Instead of bobbing up and down, oscillating wave surge converters pitch back and forth with each passing wave. The devices consist of massive hinged flaps attached to the sea floor in shallow waters. As waves pass the device they push the flap closed. That’s how the Oyster 800, built byAquamarine Power of Edinburgh, works. But instead of generating electricity at sea, the device harnesses mechanical movement to pump pressurised water to an onshore facility. There the water drives a hydroelectric turbine that can easily be maintained from shore. Aquamarine will soon begin testing its commercial-scale device, Oyster 800, an 800 kW device that is 26 metres wide and stands 12 metres tall.

Rotational Wave Energy

A rather unusual form of wave energy turns energy-harvesting devices in circles like a spinning top. Rotational wave energy employs an eccentric, or off-centre, weight that is sealed inside a buoy or ship hull and spins in rough seas. Finnish company Wello will soon begin testing the Penguin, a 500 kW rotational wave energy device. The Penguin has an asymmetrically shaped hull that causes it to roll, heave, and pitch – much like the stilted stride of a penguin – with each passing wave. The movement is used to accelerate a 95-tonne weight that spins inside the hull and drives an electric generator to produce electricity.

Oscillating Water Column

Oscillating Water Columns (OWCs) harness the rise and fall of passing waves to compress vast air reserves that drive a turbine to produce electricity. The machine sits semi-submerged on the ocean surface with a large hollow cavity open to the sea below the water line. Passing waves cause the water level inside the cavity to rise and fall, which compresses and decompresses air trapped inside the cavity above the water line.

Air flows out of the device through a vent on the surface when compressed and back in through the vent when decompressed. This moving air spins a bidirectional turbine that produces electricity regardless of direction. On 8 July this year, Voith Hydro Wavegen of Invernesss, UK completed the installation of a 300 kW OWC in Mutriku, Spain (shown here). The device, which also acts as a breakwater, is the first of its kind – a fully commercial wave energy devicethat is connected to the grid and selling power.

Overtopping device

Overtopping-wave-energy devices harvest energy by allowing water to fall from high to low elevation. As tall waves crash into the sides of an overtopping device, water spills into a reservoir that temporarily holds it several metres above sea level. The seawater is then funneled into a narrow spillway where it turns an electric turbine as it flows back into the surrounding sea. Danish company Wave Dragon tested a small-scale device capable of producing 20 kW of power from 2003-2010. A full-scale device could produce 12 megawatts of electricity but would require a massive reservoir more than 100 metres in diameter.