Wave power results from the harnessing of energy transmitted to waves by winds moving across the ocean surface. Waves contain about as much energy as the world is using today.
The best estimates for wave power is 1 terawatt (TW), the equivalent of the world's electricity production, for the waves arriving at the coast, and 10 TW for the power in the open sea. A terawatt is 1000 gigawatt (GW) or 1,000,000 megawatts (MW). For comparison, an industrialized country such as Britain has a grid capacity of around 50 GW.
In the 1970's, two countries began to realize the potential that wave energy represented. Japan and England began to develop methods for utilizing this resource for power generation.
The ultimate prize is an inexhaustible source of non-polluting energy which has still to be achieved on a large scale. But the story so far is one of a triumph of science and engineering. The difficulties which had to be overcome were immense but the major problems have been solved. But progress since the early days of the mid-1970s, when the world was galvanized by a growing energy crisis, has been remarkable.
There are essentially two types of wavepower generators: fixed devices, which attempt to harness the power of the waves crashing against the coast, and floating devices, which attempt to harness the power of the waves in the sea.
FIXED DEVICES
The Oscillating Water Column (OWC)
The founding father of wave power was Professor Yoshio Masuda, a former Japanese naval commander, who developed a principle that came to be known as the Oscillating Water Column (OWC). It eventually came to be used by the vast majority of the first generation of working devices, as in the Norwegian stations at Bergen, the Gully station on Islay, Ireland, and finally, in the OSPREY device in the United Kingdom.
The OWC was developed to solve a basic technical problem: How to harness the force of the waves so that it could make a turbo-generator revolve at 1000 rpm or more.
The Masuda's solution trapped the waves inside a hollow cylinder which was open to the sea at its base. As the waves rose and fell in the sea outside, the column of water inside the cylinder mimicked the movement –because water finds its own level. So with column of water was inside the cylinder oscillating—i.e. going up and down every seven or so seconds—it acquired the unattractive name of Oscillating Water Column. It was originally called the Masuda Device.
As the column rose, it forced the pocket of air above it to rise. The air went out through the only exit, at the top of the cylinder, which was occupied by an air turbine which revolved as the stream of air rushed through. Then, as the wave fell in a trough, the column of water descended, and air was sucked in from the atmosphere to fill the vacuum, spinning the air turbine again. A clever design with two sets of check valves was used as to guide the air stream produced on both occasions, in the same direction and subsequently provide uniform flow momentum to the turbine.
The OWC initially was used for small scale commercial applications, such as navigational light-buoys, where it was required to generate enough power to light a 60-watt bulb and driving a flasher unit. But the real significance of Masuda's invention was that it was showing that the waves themselves could be made to serve the needs of an electricity consumer instead of drawing on some other source.
The IsIay Oscillating Water Column at Islay, is perhaps the most successful energy extractor of 60 KW in operation today. The OWC chamber has been constructed at the end of a channel forming a natural estuary. The water surface within the OWC oscillate vertically in simple harmonic motion. As the surface rises it exerts an upward pressure upon an entrained mass of air which is thus displaced from the OWC through the duct and into the path of a Wells Turbine.
Another successful OWC plant was in 1985 established in Norway on Toftestallen, a small island 35 miles north of Bergen. This OWC was a 19.6-meter steel tower or chimney standing on the seabed in water 7 meters deep. There is an opening in the side, 1 meter above and the same distance below sea level, admitting the waves. As they rise to a peak outside, the column of water inside the device rises also, pushing a pocket of air up inside the chimney and out through an air turbine into the atmosphere. As the water level falls into a trough, air is sucked back in from the atmosphere to fill the vacuum. The stream of air drives the turbine—a development of a Wells turbine—so that it revolves in the same direction whether the air is coming from above or below. It can accept a burst of energy up to 1000 kW and revolve at up to 1500 rpm.
Tapered Channel Systems (TAPCHAN)
TAPCHAN, or tapered channel systems, consist of a tapered channel (hence the name) which feeds into a reservoir, which is constructed on a cliff. The narrowing of the channel causes the waves to increase their amplitude (wave height) as they move towards the cliff face which eventually spills over the walls of the channel and into the reservoir which is positioned several metres above mean sea level. The kinetic energy of the moving wave is converted into potential energy as the water is stored in the reservoir. The stored water is then fed through a Kaplan turbine .
The concept of TAPCHAN is an adaptation of traditional hydroelectric power production. Collect the water, store the water, run it past a turbine on its way out. With very few moving parts, all contained within the generation system, TAPCHAN systems have low maintenance costs and a greater reliability. TAPCHAN systems also over come the issue of power on demand, as the reservoir is able to store the energy until it is required.
Unfortunately, TAPCHAN systems are not suitable for all coastal regions. Suitable locations for TAPCHAN systems must have consistent waves, with a good average wave energy and a tidal range of less than 1 meter, suitable coastal features including deep water near to shore and a suitable location for a reservoir.
FLOATING DEVICES
Salter Duck
The Salter Duck, Clam, Archimedes wave swing and other floating wave energy devices generate electricity through the harmonic motion of the floating part of the device, as opposed to fixed systems which use a fixed turbine which is powered by the motion of the wave. In these systems, the devices rise and fall according to the motion of the wave and electricity is generated through there motion.
The Salter Duck is able to produce energy extremely efficiently, however its development was stalled during the 1980s due to a miscalculation in the cost of energy production by a factor of 10 and it has only been in recent years when the technology was reassessed and the error identified.
The S.D.E solution
S.D.E has designed a proprietary technology for production of electricity through "harvesting" sea wave motion, even in the hardest weather conditions. The company has received an advance to design its first unique power plant in India.
The SDE method consists of using sea wave motion to generate hydraulic pressure, which is then transformed into electricity. The system takes advantage of the wave's speed, height, depth, rise and fall, and the flow beneath the approaching wave. The system has a potential to produce a net of 38 KW per meter of beachfront occupied. Manufacturing cost for a 1MW system is around $500,000 and production cost is less than 1 cent per KW. Other advantages the system include protecting the coastline from the destructive forces of the sea and operating as wave breakers.
The unique design includes the capability of combining it with a desalination unit that would be independent of exterior energy sources, pollution-free, and produce desalinated water at an inexpensive rate of $0.25 per cubic meter.
© 2000 Mena Report (www.menareport.com)
