Independent Natural Resources Inc, has received a permit for a wave powered facility to desalinate water off the coast of Freeport, Texas. The company hopes that the system will be in operation by the end of the year.

The facility will be a 25 by 50 metre platform under which there will be 18 of the company’s SEADOG wave pumps. Each pump will send water up through three water wheels connected to a generator. The electricity from the generator will be used to power a reverse osmosis desalination machine.

The SEADOG pumps, each of which are about two metres in diameter, rise and fall with ocean swells to capture the energy in the ocean waves.

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The term "blue energy" refers to salinity gradient power - the energy retrieved from the difference in the salt concentration between seawater and river water. The power is generated using osmosis with ion-specific membranes.

Jan Post, at Wageningen University in the Netherlands, has researched the global potential for electric power generated in this way. His research into the practical applicability, techniques and preconditions for large-scale energy generation from salinity gradients, has shown that very high yields are possible. In the laboratory, it is possible to recover more than 80% of the energy from salinity gradients. In practice, the technical feasibility would be 60-70% and the economic feasibility a little lower than that.

Because of differences in salt concentrations, temperature and other environmental factors, there are significant differences between the continents. The highest technical potential is in Australia where 65% of the energy from salinity gradients could be recovered; South America has the lowest potential at 47%.

There are also significant differences among rivers. The Rhine has one of highest potentials among the world’s 5,742 large rivers. Jan Post estimates that the Rhine has the technical potential to generate 2.4 gigawatts of "blue energy" per annum, of which 1.4 gigawatts could be economically recovered - enough to power around 4 million households.

Jan Post believes that it will take another ten years to bring down the cost of blue energy to a competitive level and to develop membranes which are robust enough to work when the water is polluted and when living organisms accumulate on them.

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Scientists in the Netherlands have previously succeeded in generating electricity at the point where salt and fresh water mix in an estuary using a membrane. Unfortunately, the membranes are expensive and delicate, making the technique costly.

Now Doriano Brogioli of the University of Milan Bicocca in Monza, Italy, has published a paper in the Physical Review Letters which takes a different approach that promises to be much cheaper.

Two carbon electrodes are placed in the salt water and given an initial electrostatic charge - one positive and the other negative. Positively charged sodium ions are attracted to the negative electrode and negatively charged chlorine ions are attracted to the positive electrode. When fresh water flows past the electrodes, the positive and negative ions are diffused away from the electrodes. This increases the electrostatic charge between the electrodes. In other words, some of the mechanical energy in the flowing water is converted into electrical energy.

Doriano Brogioli has demonstrated the technique, which is called an electrostatic double-layer (EDL) capacitor, on a laboratory scale. He calculates that it could eventually be cost competitive with wind power without the perceived environmental problems of wind turbines.

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It has been estimated that their is sufficient energy in the world’s ocean currents to meet 3,000 times the current power needs of the the entire world’s population. The difficulty is in harnessing that energy.

Turbines and watermills need water flowing at 5 to 6 knots to operate effectively. But most of the ocean currents flow at less than 3 knots.

Michael Bernitsas, a professor in the University of Michigan, has now developed a device that works in water flowing at just 2 knots.

The machine, called a VIVACE, relies on "vortex induced vibrations". These are undulations that a rounded or cylinder-shaped object makes in a flow of fluid. The presence of the object puts kinks in the current’s speed as it skims by. This causes eddies, or vortices, to form in a pattern on opposite sides of the object. The vortices push and pull the object up and down or left and right, perpendicular to the current. These powerful vibrations regularly damage docks, oil rigs and coastal buildings.

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The US Department of Energy has awarded Lockheed Martin a contract to construct a thermal piping system to capture the ocean’s absorbed solar heat.

The energy produced could be used to generate electricity or to fuel desalination, and according to the company, the process would be harmless to the ocean’s environment.

Lockheed Martin plans to create piping wide and long enough to stretch down thousands of feet under the ocean to harness the energy available from the temperature difference between the surface and the deep ocean. The temperature variant is relatively small, so large volumes of water are needed to produce a commercially-viable amount of power.

In 1974, Lockheed and Bechtel created a small-scale prototype, which is still functional. Denise Saiki, the vice president and general manager of Lockheed’s Undersea Systems business unit said that “The next step is to demonstrate it on a commercial scale and this DOE contract will help accelerate our progress towards that goal.

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Researchers at te University of Southhampton are proposing to build a floating “Energy Island” which would harness energy from the wind, sea currents, waves, the sun and the by Ocean Thermal Energy Conversion. OTEC uses the temperature difference between surface and deep-sea water to generate electricity. Although it has an efficiency of just 1-3%, researchers believe an OTEC power plant could deliver up to 250MW of clean power. between four and eight energy islands would produce power equivalent to a nuclear power plant.

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In Washington yesterday, Scotland’s First Minister, Alex Salmond, announced a $US 20 million prize for innovators from any nation who design environmentally friendly ocean technology, such as better ways to harness tidal, wave or offshore wind power.

Mr Salmond said that Scotland wanted "to target an aspect of renewables that on one hand has amazing potential but is still in its infancy". He pointed out that Scotland has unrivalled potential to produce renewable energy in Europe, having 25% of the continent’s offshore wind resources and 10% of its wave potential.

Australia also has huge potential in offshore energy production and is a leader in developing technology for producing electricity from wave power. Australian  companies developing marine technologies include Oceanlinx (formerly Energetech) which has projects under development at Port Kembla in New South Wales and Portsea in Victoria, Seapower Pacific which is developing the CETO wave power and desalination facility off Fremantle and  Biopower Systems which is testing unique  wave and tide power system

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