Ocean energy can play important role in renewable resources mix

June 25, 2011 by admin  
Filed under Ocean Energy

Renewable technologies could supply the world with more energy than it would ever need and at a very competitive cost, avers Steve Sawyer, secretary-general of the Global Wind Energy Council.

He adds that ocean energy may play a very important role in the future. Ocean energy derives from the potential, kinetic, thermal and chemical energy of seawater, which can be transformed to provide electricity, thermal energy or potable water.

According to the Intergovernmental Panel on Climate Change (IPCC) report published recently, several technologies are possible, such as submarine turbines for tidal and ocean currents, heat exchangers for ocean thermal energy conversion, and a variety of devices to harness the energy of waves and salinity gradients.

Ocean technologies, with the exception of tidal barrages, are at the demonstration and pilot project phases and many require additional research and development. Some of the technologies have variable energy output profiles with differing levels of predictability (for instance, wave, tidal range and current), while others may be capable of near-constant or even controllable operation (for instance, ocean thermal and salinity gradient).

Tidal Power Plant in Northern Ireland
Sabine Sauter writes in Pictures of the Future about “tapping invisible rivers”.  Tidal flows represent a largely untapped source of clean energy.

Located off the coast of Northern Ireland, the world’s first commercial tidal current power plant is producing electricity for 1 500 household using energy generated by high and low tides. The Strangford Lough plant is operated by Marine Current Turbines, a British company in which Siemens acquired a 10% interest in 2010. The facility is similar to a wind turbine, the only difference being that it is driven by water instead of air. Each of its two drivetrains weighs 27 t and is equipped with a rotor 16 m in diameter.

The rotor blades can be turned through 180º, which means they can produce electricity for up to 20 hours a day regardless of whether the tide is coming in or going out.

The tower to which the two propeller turbines are attached through a cross member has a diameter of 3 m. Depending on the tide, the tower can protrude as much as 20 m above the sea. The rotors cannot be seen above the water – and it is even possible to take a small boat directly past the turbine because the rotors are located at least 3 m below the surface.

Although extensive installation costs make an investment in tidal current power plants around twice as high as those for offshore wind power facilities, the resulting electricity offers several benefits. For example, the energy density of water is 800 times higher than that of wind, which makes gene- rating electricity with water much more efficient. A 1,2 MW tidal plant like the one at Strangford Lough can produce as much electricity in a year as a 2,5 MW offshore wind turbine. The electricity yield from tidal facilities is also more precisely calculatable, which enhances planning security. After all, tidal currents are determined by the moon and the earth’s gravity, so they are not dependent on the weather and can be predicted years in advance.

The International Energy Agency estimates the global output potential of tidal power plants to be as high as 800 TWh/y, which is enough to supply 250-million households with electricity.

Marine Current Turbines continues to invest in tidal technologies. Besides other things, the company plans to start building a tidal turbine park near the Isle of Skye, in north-eastern Scotland, in 2013.

When it is complete, the facility will supply up to 4 000 households with electricity from the sea.

Article source: http://www.engineeringnews.co.za/article/ocean-energy-can-play-important-role-in-renewable-resources-mix-2011-06-24