Several floating wave energy generation devices are under development. They generate electricity as they are moved by the waves. One open-ocean method uses Salter Ducks—tethered cams that bob up and down with the waves on the surface of the water.
Salter Duck
The nodding motion of the cams compresses oil in pistons inside the devices. The pressurized oil is released through a hydraulic motor that converts 90 percent of the harnessed energy into electricity. A Scottish company, Pelamis Wave Power, has developed a floating wave energy converter known as Pelamis, named after the scientific name of a sea snake. Each device is a series of five semi-submerged tubes that are linked to each other by hinged joints. Passing waves cause each tube to rise and fall like a giant sea snake. The motion tugs at the joints linking the segments. The joints act as a pumping system, pushing high pressure oil through a series of hydraulic motors, which in turn drive the electrical generators to produce electricity. The wave energy converters are anchored to the sea floor by moorings and then connected to the grid via subsea power cables.
The Salter Duck generates electricty offshore using the movement of the waves to bob up and down on the surface of the water.
PELAMIS WAVE ENERGY CONVERTER
In 2008, Pelamis Wave Power and the Portuguese utility Enersis built the world’s first wave farm off the coast of Portugal. Three first-generation Pelamis machines had an installed capacity of 2.25 megawatts and generated sustained power to the electric grid. However, the project ended later that year, with the Pelamis machines being towed back into harbor, due to the financial collapse of Enersis’ parent company. In 2009, Portuguese electric companies EDP and Efacec purchased Enersis’ share in the wave farm and have plans to install up to 26 second-generation Pelamis wave energy converters with an installed capacity up to 20 megawatts. There aren’t yet any large commercial wave energy plants, but there are a few small ones. Wave energy devices power the lights and whistles on buoys. While some countries like Japan have active wave power programs, the only projects in the U.S. are currently experimental.
Image courtesy of Pelamis
Osmotic OsmoticPower PowerPlant Plant
Osmotic Power Plant In 2009, a Norwegian energy group, Statkraft, opened the world’s first osmotic power plant. Osmotic power is based on the natural process of osmosis—the diffusion of molecules through a semipermeable membrane from a place of higher concentration to a place of lower concentration. It is a clean, renewable energy source. In an osmotic power plant, seawater and freshwater are separated by a semi-permeable membrane—freshwater can move through the membrane but saltwater cannot. The salt content of the seawater draws freshwater through the membrane to dilute the salinity, increasing pressure on the seawater side of the membrane. The increased pressure is used to spin a turbine to generate electricity. Though Statkraft worked over a decade on bringing a large-scale osmotic power plant online, the technology is not financially competitive and the company has stopped pursuing this project.
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Exploring Hydroelectricity
www.NEED.org
Image courtesy of Statkraft
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