Survey of Energy Resources 2007
Wave Country Notes
United States of America
For a prolonged period, there was no official interest in wave energy in the USA. A number of devices were conceived but few made it past the drawing board. However, interest in wave energy has recently been rekindled, thanks in part to an extensive study undertaken by the Electrical Power Research Institute (www.epri.com/oceanenergy/waveenergy.html), which made a 'compelling case for investment in wave energy'. This interest is reflected at both a national and state level and a number of technologies have been developed.
AV's device consists of a buoy anchored to the sea floor so that it floats beneath the surface (www.avinc.com/energy_lab_project_detail.php?id=68). As the float moves through the water vertically, responding to changes in pressure resulting from passing waves, it powers a generator on the sea bed (mechanism unspecified). A scale model completed testing in the Pacific Ocean with encouraging results, and plans for broad deployment are being developed. This concept is at the R&D stage.
Ocean Motion International
Ocean Motion International's technology uses a large buoyant vessel to which a number of heavy ballast masses are attached via a sleeve-type pump. The masses rise and fall in the waves, pumping water into a manifold to power a hydroelectric generator or a reverse osmosis (RO) unit. This concept is at the R&D stage (www.oceanmotion.ws).
Ocean Power Technologies (OPT)
OPT has a long history of developing its PowerBuoyTM. This system consists of a floating buoy that is moored to the sea bed so that it can freely move up and down in response to the waves. The movement is converted into rotational mechanical energy, which in turn drives the electrical generator, all of which are in a sealed unit. The control system collects data and adjusts the performance of the PowerBuoyTM system in real-time and on a wave-by-wave basis. The current device is about 17 m long, 3 m in diameter and is rated at 40 kW but OPT has plans for a 500 kW PowerBuoyTM system, with a diameter of nearly 14 m and a length of 20 m (www.oceanpowertechnologies.com). OPT has deployed single devices in Atlantic City (New Jersey) and Oahu (Hawaii) and has an agreement for another device at Santoña (Spain). Typically, these agreements allow OPT to demonstrate the performance of its device before going on to install arrays. OPT is the only wave energy developer to have successfully floated on the stock market, but it is expected that others will try to follow in 2007/8.
Independent Natural Resources, Inc. (INRI)
INRITM has recently developed the SEADOGTM pump (www.inri.us). This comprises a large piston operating over an air-filled buoyancy chamber. The piston moves up and down with the varying pressure under wave peaks and troughs and this movement drives a hydraulic pump to produce pressurised water, which is pumped to shore to produce potable water (via an RO unit) or electricity by filling a reservoir which is allowed to drain back to the sea via hydroelectric turbines. Each pump can produce several tens of kilowatts of power, so in practice an array of devices will be deployed. A single SEADOGTM prototype has been successfully tested in the Gulf of Mexico and the company has plans for deployment of a 16 device array off the Californian coast, which will produce just over 500 kW.
Scientific Applications & Research Associates (SARA)
SARA has developed a wave energy device to extract energy from waves using a magnetohydrodynamics (MHD) generator. It is designing a 100 kW prototype to demonstrate this principle, as well as developing a deep-ocean-moored device to use the MHD generator. This device is at the R&D stage (www.sara.com).
Seavolt's Wave Rider consists of a moored cam-shaped buoy which bobs up and down in the waves. This rolling action powers a hydraulics circuit connected to a motor and generator. The current status of this device is uncertain.