Oscilla’s wave energy harvesters are based on a phenomenon called magnetostriction, a property of some ferromagnetic materials to change their shape slightly in the presence of a magnetic field.
However, Oscilla applies this process in reverse – called reverse magnetostriction – by applying stresses or strains to the materials so their magnetic characteristics change. When coupled with a generator that has permanent magnets and wire coils, the process generates electricity.
Oscilla owns a number of patents and pending applications covering its technology, including two related U.S. Patent Nos. 7,816,797, and 7,964,977, entitled “Method and device for harvesting energy from ocean waves.”
These patents are directed to a device (100) for harvesting energy from the oscillations of ocean waves (102). The core modules of the device (100) include at least one buoy (104) attached to magnetorestrictive elements (106) via tethers (110).
The magnetorestrictive elements (106) are anchored to the seafloor or to another rigid body using anchors or weights (108).
According to the Economist piece, the magnetorestrictive elements are bars made from a strongly magnetic alloy of iron and aluminum. These bars need be compressed only very slightly (one part in 10,000) to generate electricity.
Even such a tiny compression takes a large force when the bar is made of solid metal, but ocean waves have sufficient power to generate the required force and do so by oscillation. Oscilla’s generators have two large objects connected by cables:
A buoy floating on the surface of the ocean contains the generating apparatus of alloy bars, magnets and coils, as well as sets of hydraulic rams which can squeeze the bars. The cables connect the buoy to a heave plate maintained in a stationary position.
As the buoy rises and falls with the waves at the surface and the heave plate stays still, the tension on the cables increases and decreases. The changing tension drives the rams and produces electricity.
Because the generators operate on changing tension, they don’t need to employ lot of moving parts and should therefore be more reliable than conventional wave power generators.
After a successful trial of a four-meter prototype last year, Oscilla hopes to build a full-scale device by 2018.