30-08-2014, 04:42 PM
Tidal Energy
Tidal Energy.ppt (Size: 578.5 KB / Downloads: 291)
disadvantages
Presently costly
Expensive to build and maintain
A 1085MW facility could cost as much as 1.2 billion dollars to construct and run
Connection to the grid
Technology is not fully developed
Barrage style only produces energy for about 10 hours out of the day
Barrage style has environmental affects
Such as fish and plant migration
Silt deposits
Local tides change- affects still under study
Advantages
No pollution
Renewable resource
More efficient than wind because of the density of water
Predictable source of energy vs. wind and solar
Second generation has very few disadvantages
Does not affect wildlife
Does not affect silt deposits
Less costly – both in building and maintenance
Wave Facts
Waves are caused by a number of forces, i.e. wind, gravitational pull from the sun and moon, changes in atmospheric pressure, earthquakes etc. Waves created by wind are the most common waves. Unequal heating of the Earth’s surface generates wind, and wind blowing over water generates waves.
This energy transfer results in a concentration of the energy involved: the initial solar power level of about 1 kW/m2 is concentrated to an average wave power level of 70kW/m of crest length. This figure rises to an average of 170 kW/m of crest length during the winter, and to more than 1 MW/m during storms.
Wave energy performance measures are characterized by diffuse energy, enormous forces during storms, and variation over wide range in wave size, length, period, and direction.
Wave energy is an irregular and oscillating low-frequency energy source that must be converted to a 60-Hertz frequency before it can be added to the electric utility grid.
Oscillating Water Columns
The Nearshore OWC rests directly on the seabed and is designed to operate in the near-shore environment in a nominal mean water depth of 15m.
Nearshore OWC units also act like artificial reefs, improving environments for fishing while calming the water for a harbor.
OWC designs typically require high maintenance, costly, taut moorings or foundations for operation while only using the extreme upper strata of an ocean site for energy conversion. While focusing devices are less susceptible to storm damage, massive structuring renders them most costly among wave power plant types.
Since 1965, Japan has installed hundreds of OWC-powered navigational buoys and is currently operating two small demonstration OWC power plants. China constructed a 3 kW OWC and India has a 150 kW OWC caisson breakwater device.
A 75 kW shore-based demonstration plant by Queens University, Belfast, using the OWC process described above has operated on the Scottish island of Islay for 10 years
Floating Devices
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. In these systems, the devices rise and fall according to the motion of the wave and electricity is generated through their motion.
The Salter Duck is able to produce energy very 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.
Tapered Channel Wave Power
These shoreline systems consist of a tapered channel which feeds into a reservoir 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 meters 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 water then passes through hydroelectric turbines on the way back to sea level thus generating electricity.
This vs. That
Advantages
The energy is free - no fuel needed, no waste produced.
Most designs are inexpensive to operate and maintain.
Waves can produce a great deal of energy.
There are minimal environmental impacts.
Disadvantages
Depends on the waves - sometimes you'll get loads of energy, sometimes nothing.
Needs a suitable site, where waves are consistently strong.
Must be able to withstand very rough weather.
Disturbance or destruction of marine life
Possible threat to navigation from collisions because the wave energy devices rise only a few feet above the water.
Degradation of scenic ocean front views from wave energy devices located near or on the shore, and from onshore overhead electric transmission lines.