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Wave power schemes in the future require a large surface on the sea.
Although suggested 35 years ago, wave generators now need development. A load factor of 30 to 40% is expected and here are some of the prospects:-
Buoy generator.
Ocean Power Technology (OPT) say that a wave farm covering 300 sq miles of the pacific could supply all of California's homes and the cost would be competitive.
Each buoy has a steel column which sits vertically in the water, a large circular collar moves up and down the column as the waves pass. Each wave generator converts vertical motion into mechanical energy which drives a generator. Most of the structure is underwater so electrical power is fed to shore via a cable.
Vivace (energy created by vortex induced vibrations) development.
Energy from vibrations can be destructive and are engineered out of designs, structures etc. Failure to do so resulted in the collapse of the 1800 m long Tacoma Narrows Road Bridge in Nov 1940 where the whole bridge was set in torsional vibrations by strong winds. The energy to set up these destructive forces was induced from wind blowing across the bridge which produced vortices setting the bridge into a twisting motion. Another example of wind induced vibrations caused collapse of the Ferrybridge UK cooling towers in 1965.
Prof. Michael Bernitsas at the university of Michigan is developing a Hydro Kinetic Energy System which uses vortices in the water currents (moving at 1 to 3 mph) flowing across cylindrical tubes which vibrate up and down on springs creating energy harnessed to generate electrical power. The system would be located on the river or sea bed.
The prototype for the Detroit River field test has 8 cylinders, 25 cm dia and 2 m long (ref 202.)
The future projected cost of 5 cents/kwhr is competitive with nuclear or wind power. The electrical power density could however be higher than for wave, tidal or wind turbine farms and it would have a high load factor or be continuous, not requiring so much diversity and energy storage capacity systems attached to the transmission grid.
SSE - Alstom doughnut wave generator.
A projected 200MW wave generator based on prototype where waves act on a muticell array of flexible membranes which compress air which is ducted to drive a turbo gneerato. Electrical power is fed to shore by cable.
Pelarmis
A 'Pelarmis' wave generator consists of four tubular cylinders connected end to end floats on the ocean surface (looks like a worm 160 meters long.)
Wave induced motion is resisted by hydraulic rams which pump oil into a smoothing accumulator. The latter drains into a hydraulic motor coupled to an electric generator, 75 kW per Pelarmis.
A 40 unit wave farm in the Orkneys (Scotland) will provide up to 3 MW. A larger 20 MW wave farm is being built off Portugal. The long term idea is to expand to 550 MW from wave power off the Portuguese coast.
Orecon wave generator
A 40X40 m structure anchored to sea bed could produce up to 1.5 MW from wave induced oscillating water columns.
'Wave Hub', covering an area 4 X 2 km and 10 km from the coast is planned to provide 60 MW from 2015 from turbines built by Fred Olsen, West Wave (EON) and Ocean Prospect.
Wave Dragon
Waves are funneled up to the top of a reservoir 16 m above sea level which then flow back via kaplan turbines which drive permanent magnet generators.
CETO wave generator
Passing wave movement moves undersea floats causing pumping of sea water to onshore Pelton wheel with generator. Power is used for local desalination and electrical supply.
Energen are developing a device which operates in waves under the surface near a shore where 'torque tubes' act together with wave motion to pump oil through a hydraulic system to drive a turbine / generator.
Sea Raiser Wave - Hydro plan
Sea raiser is a plan to use wave energy to pump water to a high reservoir on land. This will enable flow back to the sea with power drawn from turbines when demand high and /or in calm conditions.
200m rubber tubes - Sea Snake
QuinetiQ plan to develop 'sea snakes' operating around the shores, each capable of generating 1 MW. These are a 200 metre long rubber tube tethered to face into the waves, located beneath the water level.
The tubes are continually squeezed by the ocean waves which cause bulges in the tube which travel along and drive a turbine in the tail end. A 9 metre long sea snake has been tested and a full scale prototype could be operational in 3 years. Many would be tethered along the shore lines and would largely be out of sight.
Note - Tests on these schemes will clarify the claims of power/area some which are ambitious. l
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