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Ship-based system designed to harness energy from waves


July 18, 2011

A proposed wave-power system could be installed on ships, which would regularly return to shore to deliver power to the grid (Image: Fraunhofer)

A proposed wave-power system could be installed on ships, which would regularly return to shore to deliver power to the grid (Image: Fraunhofer)

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Why don't we have stationary commercial fishing platforms that are anchored offshore, where they sweep the waters with their nets, sending the captured fish back to shore through a pipeline? Well, because it's simpler and more efficient to send fishing boats out to catch the fish and bring them in. Thinking along those same lines, the Fraunhofer Center for Manufacturing Innovation has proposed a ship-mounted renewable energy-harvesting system, that would be powered by the ocean's waves.

Traditional wave-power systems, both actual and proposed, are typically permanently located out at sea. Because of this fact, they must be designed to withstand storms. They are also required to send the power that they generate back to shore via underwater cables, which can be very costly to purchase and install. Additionally, because they are permanent structures, they must meet regulatory standards and can't be located anywhere that ships might run into them.

The Fraunhofer system would apparently have none of these problems. It would consist of floating buoys, that would be deployed over the sides of a 50 meter (164 foot)-long ship, on hinged arms. As those buoys proceeded to bob up and down on the waves, the arms to which they were attached would pivot up and down, generating power that would be stored on an onboard battery system. One the ship was ashore, power from those batteries could then be released into the municipal grid system, during hours of peak usage.

Because the system would be mobile (the buoys would be lifted out of the water when the ship was moving), everything could simply be taken to shore when storms were approaching. No cables would be required, and the system could be temporarily parked wherever it didn't pose a hazard and the waves were decent.

The ships, which could be repurposed existing vessels, would have a storage capacity of 20 megawatt-hours. It is estimated that the system could generate electricity at a cost of 15 cents per kilowatt-hour, which is lower than the cost of existing wave power systems, that reportedly range between 30 and 65 cents.

Of course, some energy would be expended to power the ships' engines, or the engines of tug boats that would tow them.

Source: New Scientist

About the Author
Ben Coxworth An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away. All articles by Ben Coxworth

Yea.. great thinking - teams all around the world are working on a more efficient way to store electricity created by solar panels, because using batteries isn\'t really a good option. But it would be a great idea to load a ship with batteries and send it out to the sea? What would such batteries cost? What would be their life cycle? If such ship sinks - would it be the ecological impact? Solving peaks by battery ships - which may or may be not loaded since they have to rely on good weather conditions, now that sounds great right? This doesn\'t sound too good by me.


\"Why don\'t we have stationary commercial fishing platforms that are anchored offshore, where they sweep the waters with their nets, sending the captured fish back to shore through a pipeline? Well, because it\'s simpler and more efficient to send fishing boats out to catch the fish and bring them in.\" Who came up with that answer? They are wrong. It would be simpler and more efficient to pipe the fish to land. Real answer: It would require a huge investment in a system that would put people out of work. There is no economic incentive since we are not yet knowingly suffering from a short supply of fish versus demand.

I think this boat idea is stupid. However, it gave me an idea. create a huge sheet of piezo-electric material, say the size of a football field. sandwich this inside a more rugged but flexible material. sparsely, but evenly distribute ballast along the bottom. put it out to sea with a conduit of wire feeding the electricity back to land.

Facebook User

Since the ship would be moving up and down with the waves, most of the energy (of the waves) would not be harvested. The diagrams seem to indicate that the ships rocking side to side would deliver the most energy to the side arms as shown in the diagrams. I would suggest it be tethered to the bottom or to a heavy weight so as to capture more energy. Or even a floating upended tube like they put oil rigs on that don\'t move up and down as much. Also, batteries would be to expensive to store the energy. I would suggest using the energy to electrolize sea water to separate out the hydrogen. that hydrogen could then be off loaded to a ship and brought ashore and burned to produce electricity with only water vapor as its exhaust. Why aren\'t most solar or energy capture systems converting their energy to hydrogen for storage or later use? land based solar collectors are starting to use molten salts to store energy which can turn solid in the system if it isn\'t kept hot enough. Seems safer to me to make hydrogen and burn it later thru the night as needed for energy. Piping hydrogen from a solar collector to a power generator station far away (closer to the end user) would make more since, but perhaps not at sea.

Paul Canada

Maybe one of those wireless power methods like lasers or whatever might become economical if the tech improves and cost goes down. You might be able to have many more potential transmission opportunities without having to dock at port so the boat would not have to travel as far after harvesting energy.

I agree that this idea would be better served with some of the other storage methods being developed but if wireless transmission could be made practical it would mean that most of the storage would be on land or at a fixed offshore instillation. Ships would only need to store energy when out of contact with a receiver. I wonder if some of those old lighhouses might be renovated into receivers.

Snake Oil Baron

I like the hydrogen idea. Batteries? Yuk. Maybe lead-acid, since weight is not a problem.

Captain Obvious

This is silly. How can a system that requires wave energy converters, a ship, batteries, and a crew produce electricity for less than the wave energy converters alone? I can\'t believe Fraunhofer would put their name on such poppycock.


A boat with articulated hulls would be better - with hydraulic rams driving pump-driven generators. You could have a snake-like boat arching over the waves, harvesting power with each peak and trough - an existing concept is the \'seansnake sea train\' http://www.seasnake.net/


Hello from Argentina, are touching and admirable the many efforts of so intelligent and committed people to reduce the effects of global warming. Unfortunately I am able to assure you, in my infinite shame, that in mediocre countries like mine for at least 99% of people, this is an irrelevant issue . Moreover, the waste of energy is driven by the government. In our case we are 40 million people happily polluting the earth. Greetings Adrian panchalino@yahoo.com


@ Paul Canada - The biggest reasons why hydrogen electrolysis is not user to store energy right now: It\'s inefficient at production less than 10% of the electricity is converted to hydrogen. It\'s inefficient at the consumption less that 40% of the hydrogen is converted to electricity when burned or run through a fuel cell. (For a total efficiency around 5%) It\'s expensive electrolysis requires platinum which is running 1800usd/oz making a commercial scale system multibillion dollar venture. Hydrogen is an escape artist and requires large heavy cylinders to store.

However if some technologies make it to market it may become a feasible option. The platinum may be replaces with a doped carbon nano-tube cathode that costs 2-5% of platinum and is more efficient Another CNT material could replace platinum in the fuel cell also making it more efficient and longer lasting than a platinum cathode model. There is a similiquid material that may be able to store hydrogen better than tanks and would be stable until heated.

So at present hydrogen electrolysis is inefficient expensive and the product difficult to store at present. Future tech may be able to reduce these but most are 5-10 years from fruition. So new chemistry batteries are currently a more efficient less expensive storage medium.


Generating electricity on such a ship would be foolish. Converting the wave action directly into compressed air would be a lot more efficient, and with nitrogen filters on the air intakes you would not have to worry about oil getting into the compressors. The heat generated by compression could also be tapped for additional power.


Just sink a bunch of Tidal generators and use the tidal currents.

Or use a concrete vacuum anchor and a sea snake or tidal generator to power a heatpump and enclosed steam generator bobbing in a floating cylinder.

Then have a single core cable laid on sea bed and use DC current to take the energy produced to land. The return goes through the sea. That\'s how Norway transmits power to Denmark.

When is a company going to think about a sea based geothermal energy plant???? No one owns the land in international waters...

Karsten Evans

I don\'t get it. Why build a ship to harvest energy and take it back to shore? Why not use such ideas (like the hydraulic rams) to power real ships. As a bonus the energy absorbed could actually dampen the wave motion for passengers and make for a smoother ride. I don\'t know if this idea is practical, but I think it\'s worth looking into.


Some good comments. See MINESTO u/w stunt kite with turbine 500KW. Also see PELAMIS the sea snake. The latter inherits the technology (super duper hydraulic pumps) from SALTERS DUCK. Salters Duck was a hull with extremely evil rolling characteristic. Moored in a wave power area, the hull contained a heavy inertial pendulum , coupled to a very sophisticated high efficiency hydraulic accumulator/ generator. The electricity was cabled ashore. There was a considerable breakwater effect . Producing Hydrogen is inefficient, despite the BROWN`S GAS believers. Compressing Air is inefficient, talk to some SCUBA divers about compressors. The MINESTO is fascinating. Started by SAAB as a windpower automatic superkite, now the same aerobatics (?) enable high cross-current velocities in a leisurely tide stream. The kit fits in one big road container, 20tons, and is seabed anchored with its electric cable. Interesting spin off is that it will be impossible to over-fish over the wide area to be swept out by each 500KW module. Good for the environment?


johndog --- Compressing and storing nitrogen is a lot more efficient than generating and storing electricity. The high-presser tanks have a much longer life than batteries as well.


Compressing gas always produces large amounts of heat, which may be wasted or used for heating buildings, raw materials, etc. Release of pressure produces a great drop in temperature with attendant icing problems. A power storage scheme in England takes surplus electricityand compresses gas, using the waste heat for space heating. The (liquid ) gas is stored, and later expanded through heat exchangers which draw heat from water sources. This gives extra pressure at the turbine and an overall efficiency of about 50% in terms of the electricity returned to the grid. This is a form of Heat Pumping, and would work well in the context of an ocean- going power generator. The financial viability of gas compression systems has to be taken into account. If the heat energy released cannot be \"sold\" to another user, most of the electrical compressor KWH is wasted. If groundwater or seawater low grade heat is available, it can be drawn into the cryogenic expansion system with great benefits. Of course, it takes great skill to manage a heat exchanger design which will not ice up in sub sub zero surface temperatures.


johndog--- In my original post I mentioned that the heat generated by the compression could be tapped as a energy source. The nitrogen filter does not allow water vapor through so there will be no icing inside the mechanism when using the compressed nitrogen, and the cold can be used generate electricity using a sterling cycle engine.


@ Paul Canada \"Since the ship would be moving up and down with the waves, most of the energy (of the waves) would not be harvested.\" I disagree. You should be able to get almost double the power of a stationary platform. Waves have a wavelength and if the ship is half a wavelength (or 1.5 wavelengths, etc) from the \"bobbers\" then the ship and the bobbers would be out of pahse and energy would be generated by both motions. When the bobbers were up, the ship would be down and vice versa. maybe super capacitors is a better storage medium than batteries, they\'re really coming of age. Some buses in China use capacitors instead of batteries because you can charge them as fast as you provide the current.


warren52nz - July 26, 2011 @ 08:11 pm PDT

The ship would most likely be large enough to overlap many waves, so it will float with very little vertical moment.


Good idea to harness wave energy. In fact wave energy is under utilised. A very novel approach.

Anumakonda Jagadeesh
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