Published on Jan 28, 2016
Tidal energy is an essentially renewable resource which has none of the typical environmental impacts of other traditional sources of electricity such as fossil fuels or nuclear power. Changing the tidal flow in a coastal region could, however, result in a wide variety of impacts on aquatic life, most of which are poorly understood. Tidal power works because of the Moon's constant rotation around the Earth.
This is very convenient because scientist's can predict the electricity production on a daily basis. .
The tides produce the electricity for tidal power by flowing in and out of turbines . A hydrostatic head or adequate water height difference on either side of the turbine.
Tidal energy works from the power of changing tides. Tidal changes in sea level can be used to generate electricity, by building a dam across a costal bay or estuary with large differences between low and high tides. The high tides allow immense amounts of water to rush into the bay. The gates of the dam then shut when water level is at its maximum height. Holes in the bottom of the dam let water (at great speed and pressure) to rush past turbines. The flow of water generates enough power to turn the turbines which creates electricity. The entire process repeats with each high tide.
Two current technologies which are used to harness the kinetic energy of tidal flow:
1) Drag Devices Water wheels :
• insufficient compared to other modes of generation
• blade speed can not exceed that of the current
2) Lift Devices Turbines :
• wind mill technology applied to liquid environment
• more efficient then drag devices
• refined propeller achieves speeds several times faster then the current
How it works
Tidal power works rather like a hydro-electric scheme, except that the dam is much bigger. A huge dam (called a "barrage") is built across a river estuary. When the tide goes in and out, the water flows through tunnels in the dam. The ebb and flow of the tides can be used to turn a turbine , or it can be used to push air through a pipe, which then turns a turbine . Large lock gates, like the ones used on canals, allow ships to pass. If one was built across the Severn Estuary, the tides at Weston-super-Mare would not go out nearly as far - there'd be water to play in for most of the time. But the Severn Estuary carries sewage and other wastes from many places ster out to sea. A tidal barrage would mean that this stuff would hang around Weston-super-Mare an awful lot longer.
The Blue Energy Ocean Turbine acts as a highly efficient underwater vertical-axis windmill. Sea water is 832 times denser than air and a non-compressible medium, an 8 knot tidal current is the equivalent of a 390 km/hr wind. Developed by veteran aerospace engineer Barry Davis, the vertical-axis turbine represents two decades of Canadian research and development. Four fixed hydrofoil blades of the Blue Energy Ocean Turbine are connected to a rotor that drives an integrated gearbox and electrical generator assembly. The turbine is mounted in a durable concrete marine caisson which anchors the unit to the ocean floor, directs flow through the turbine further concentrating the resource supporting the coupler, gearbox, and generator above it.
These sit above the surface of the water and are readily accessible for maintenance and repair. The hydrofoil blades employ a hydrodynamic lift principal that causes the turbine foils to move proportionately faster than the speed of the surrounding water. Computer optimized cross-flow design ensure that the rotation of the turbine is unidirectional on both the ebb and the flow of the tide.
The design of the Blue Energy Ocean Turbine requires no new construction methodology: It is structurally and mechanically straightforward. The transmission and electrical systems are similar to thousands of existing hydroelectric installations. Power transmission is by submersible kV DC cabling and safely buried in the ocean sediments with power drop points for coastal cities and connections to the continental power grid. A standardized high production design makes the system economic to build,install&maintain.
The Blue Energy Ocean Turbine can be arranged in four distinct and flexible platforms
Micro Power System - This is a 5 to 25kW assembly to service the remote domestic consumer.
Midrange Power System - Blue Energy is preparing to install a 500kW ocean energy system. Using two 250kW Blue Energy ocean turbines, this unit will be off grid competitive initially, and in three to four years time be grid competitive. Suitable for use in remote communities, industrial sites, and resorts in regions with net metering policies or dependence on costly and polluting diesel generation.
Blue Energy Power System - For large scale power production, multiple turbines are linked in series to create a tidal fence across an ocean passage or inlet. These are large scale, site specific, custom engineered energy installations which will vary in size and output by location. These structures have the added benefit as a transportation solution.
Mega Power System - A scaled-up version of the Blue Energy Power System, the mega class is a tidal fence capable of producing thousands of megawatts of power. These tidal fences can be many kilometers long and can operate in depths of up to 70 meters.
Rather like an underwater wind farm. This has the advantage of being much cheaper to build, and does not have the environmental problems that a tidal barrage would bring.
Tidal turbines are the chief competition to the tidal fence. Looking like an underwater wind turbine they offer a number of advantages over the tidal fence. They are less disruptive to wildlife, allow small boats to continue to use the area, and have much lower material requirements than the fence.
Tidal turbines function well where coastal currents run at 2-2.5 m/s (slower currents tend to be uneconomic while larger ones put a lot of stress on the equipment). Such currents provide an energy density four times greater than air, meaning that a 15m diameter turbine will generate as much energy as a 60m diameter windmill. In addition, tidal currents are both predictable and reliable, a feature which gives them an advantage over both wind and solar systems. The tidal turbine also offers significant environmental advantages over wind and solar systems; the majority of the assembly is hidden below the water
SMALL SCALE TIDAL POWER:
Although harnessing the tides for electrical (or mechanical) energy is not new, it's not widely implemented; because, basically a barrage is to be build. The Bay of Fundy, which experiences the world's largest tides, is one location that produces tidal electricity. This tidal power can also be utilized for small scale power production. Basically, the device would be anchored to the bottom of the ocean by a post (with gear notches along one side), just a bit further than the low tide mark. A floating section, provided by a large buoyant device would then float on the surface of the water.
The relative motion between the buoyant section and the post would produce energy, via a gear system that engages the teeth on the post. Obviously the relative motion is quite small... a tide may only rise a few feet. The brawn comes from how the gears are implemented, and how much force the floating section can produce. The floating section should to be fairly light, and having it ride the ocean back to low tide wouldn't produce enough force (only the force of gravity) to generate power.
Wave power (and tidal power) are beginning to come into their own. Benefits Deep Ocean.
Renewable and sustainable resource
Reduces dependence upon fossil fuels
Produces no liquid or solid pollution
Little visual impact
Construction of large scale offshore devices results in new areas of sheltered water, attractive for fish, sea birds, seals and seaweed
Present no difficulty to migrating fish (except tidal fences)
Shelter the coast, useful in harbor areas or erosion zones
Resource exists on a worldwide scale from deep ocean waters
Short time scale between investing in the modular construction and benefiting from the revenue
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