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
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.
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.
http://www.seasnake.net/
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.