Sunday, March 28, 2010

Wave and tidal power

The Scottish Government recently announced that 10 wave and tide power schemes capable of generating up to 1.2GW (costing about $7.6 bn to build generator and transmission lines) in total to be built around the Orkney islands and on the Pentland Firth on the northern coast of the Scottish mainland (which have some of the strongest tidal currents in the world) to power about 750,000 Scottish homes by 2020. Scotland plans to become the "Saudi Arabia of marine energy".

Wave energy technology uses the movement of ocean surface waves to generate electricity, while tidal power is based on extracting energy from tidal movements and the water currents that accompany the rise and fall of the tide. Both have to big advantages over other renewable resources - ocean tides are totally predictable and regular (wave power is dependent on the weather), and wave energy could be more abundant than tidal energy (while being less intermittent than wind or solar power). On the flip side, conditions along coastlines or on the ocean surface can be hard on wave and tidal installations and generation assets must be built with operational hazards – such as crashing waves and corrosive salt water – in mind.

Wave energy is captured using floating/semi-submerged "power modules" (which are essentially some form of inter-connected long tubes with hydraulic rams, which work like pistons, attached to them). As the long sections twist and turn in waves they pull the rams in and out of the modules like pistons, and the huge force of the rams is harnessed to run generators in the power modules and the electricity is then fed into an offshore grid via undersea cables. Tidal energy is captured using underwater turbines (or underwater windmills whose rotors are driven by currents and not wind) that gathers the energy from the powerful surges of water tides pushed through it.

Though wave and tidal power technologies have great potential, they still must prove themselves before they can be widely deployed. Harnessing these resources will depend on the success with development of near-shore and deep-water technologies. Currently, wave and tidal technologies can be three to four times more expensive than wind power per megawatt and will therefore require massive government tariff support for any viability.

The best wave climates – with yearly average power levels of 20 to 70 kW per meter of wave front or higher – are where strong storms occur like along the coasts of the Americas, Europe, Southern Africa, Australia, and New Zealand.

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