19-07-2014, 02:17 PM
Underwater windmill
Underwater windmill.doc (Size: 290.5 KB / Downloads: 29)
INTRODUCTION
I just did a Search here for "underwater" and "windmill" and it came up blank, so if this idea really has been posted here using some other verbiage,
Anyway, this Idea should be somewhat obvious in hindsight. We build ordinary windmills to extract useful power from wind energy. We put turbines in rivers (usually accompanied by dams) to extract useful power from downhill water flow. The second is more "energy intensive" than the first, which is why we all know that dams are great sources of electrical power, while electric-generator windmills spent decades in the economic doldrums (return on investment --ROI-- is relatively tiny, and only recently proved viable on a large scale).
Anyway, putting the equivalent of a windmill in a steady ocean current, say the Gulf Stream, should have an automatically-viable ROI that is intermediate between windmills and ordinary hydropower. This is because water is something like a thousand times denser than air, so a volume of flowing water contains a thousand times the energy of an equal volume of equally-flowing air.
Do note that the ocean has different currents at different depths. I once read somewhere that near the seafloor underneath the Gulf Stream is another current going the opposite direction. If true, then we can build towers on the seafloor, just like ordinary windmills, to extract power. Being so deep will protect them from ships, and most sea life is found at other depths, so they won't be bothered. Also, another thing that protects sea life is the fact that underwater windmills will have a SLOW rotation rate, due to that same greater density of water over air. This means we can also put windmills in the rich-life upper ocean currents; animals will have time to dodge the blades. (Some life forms, like barnacles, need to be discouraged; probably everything needs to be coated with Teflon or something even more slippery.)
Consider buoyant windmill modules can be anchored by cables to the bottom. They float up to perhaps fifty meters beneath the surface, in the midst of the ocean current. There they stay and generate power (which flows down those same anchor cables, and then toward shore).
Finally, it may be necessary to build all underwater windmill modules in counter rotating pairs. Again, this is because the water is denser than air; and for every unit of force that tries to rotate the blade, there will be reactive force against the generator assembly, Counter rotating blades will let such forces be canceled.
Tidal currents are being recognized as a resource to be exploited for the sustainable generation of electrical power. The high load factors resulting from the fluid proper- ties and the predictable resource characteristics make marine currents particularly attractive for power generation. These two factors makes electricity generation from marine currents much more appealing when compared to other renewables. Marine current turbine (MCT) installations could also provide base grid power especially if two separate arrays had offset peak flow periods. This characteristic dispels the myth that renewable energy generation is unsuitable on a large scale.
UNDERWATER WINDMILL DEFINITION
Tidal stream turbines are often described as underwater windmills. They are driven by the kinetic energy of moving water in a similar way that wind turbines use moving air. The generator is placed into a marine current that typically results when water being moved by tidal forces comes up against, or moves around, an obstacle or through a constriction such as a passage between two masses of land. There are sufficient numbers of such fast-flowing underwater currents around the world to make this form of marine renewable energy worth pursuing. In figure 1, the areas between the coasts of Ireland and Scotland that are colored magenta would merit the application of tidal current capturing systems. Harnessing the marine currents could also help fulfill the Climate Change Committee’s recent request in 2010 that calls for an almost complete.
decarburization of the UK’s electricity supply by 2030. In their report, Future Marine Energy, published in 2006, the Carbon Trust estimated that tidal stream energy could meet 5% of the UK’s electrical energy needs, reducing the country’s dependence upon carbon intensive imported fossil fuels. Other studies have predicted that tidal generators could produce up to 10% of the UK’s electrical energy needs. A point not lost on the UK government and the devolved administrations who see the industrial growth opportunities that tidal and wave energy could offer. Tidal flows have the advantage of being as predictable as the tides that cause them; both in terms of timing and in judging their maximum velocity. This long-term predictability helps greatly in electricity generation, enabling more efficient grid management and thus reducing the total amount of power that needs to be generated.
PRINCIPLES
Underwater turbines operate on the same principles that wind turbines use; a flow of fluid moves a set of blades creating mechanical energy which is then converted to electrical energy. They are equally troublesome for environmentalists, as wind turbines interrupt bird flights just as water turbines can disturb underwater life. One advantage water turbines enjoy over other sources of renewable energy is a predictable tide table.
MCT's ocean energy device works on the same principles as a windmill, where large underwater rotors, shaped like propellers, are driven by the huge mass of flowing water to be found at certain places in the sea. The technology consists of rotors mounted on steel piles (tubular steel columns) set into a socket drilled in the seabed. The rotors are driven by the flow of water in much the same way that windmill rotors are driven by the wind, the main difference being that water is more than 800 times as dense as air, so quite slow velocities in water will generate significant amounts of power. The energy generated, being derived from tides has the added significant advantage of being predictable
WORKING
Underwater turbines rely on tides to push water against angled blades, causing them to spin. These turbines can be placed in natural bodies of water, such as harbors and lagoons that naturally feature fast-moving flows of water. These turbines must be able to swivel 180 degrees to accommodate the ebb and flow of tides, as demonstrated by the SeaGen prototype turbine in Ireland. As the blades spin, a gearbox turns an induction generator, which produces an electric current. Other devices can be tethered and attached to a float, such as the Evopod in England. This design allows the face of the turbine to always face the direction of the current, much like a moored boat does.
Many wave power machines are designed to capture the energy of the wave's motions through a bobbing buoy-like device. Another approach is a Pelamis wave generator, now being tested in Scotland and in Portugal, which transfers the motion of surface waves to a hydraulic pump connected to a generator.
Tidal power typically uses underwater spinning blades to turn a generator, similar to how a wind turbine works. Because water is far more dense than air, spinning blades can potentially be more productive than off-shore wind turbines for the same amount of space.
In addition to being renewable, another key advantage of ocean power is that it's reliable and predictable, said Daniel Englander, an analyst at Greentech Media.
Although they can't generate power on-demand like a coal-fired plant, the tides and wave movements are well understood, giving planners a good idea of energy production over the course of year.
There are only a few underwater turbines in operation today and they all operate like underwater windmills, with their blades turning at right angles to the flow of the water. In contrast, the Oxford team's device is built around a cylindrical rotor, which rolls around its long axis as the tide ebbs and flows. As a result, it can use more of the incoming water than a standard underwater windmill
Power Generation by Underwater Windmill And Cost
Energy derived from the moon now trickles into an Artic tip of Norway via a novel underwater windmill like device powered by the rhythmic slosh of the tides. The tidal turbine is bolted to the floor of the Kvalsund channel and is connected to the nearby town of Hammerfest’s power grid on September 20th. This is the first time in the world that electricity directly from a tidal current has been feed into a power grid. The gravitational tug of the moon produces a swift tidal current there that cause though the channel at about 8 feet (2.5 meters) per second and spins the 33-foot (10 meters) long blades of the turbine. The blades automatically turn and rotate at a pace of seven revolutions per minute, which is sufficient to produce 700,000 kilowatt hours of non-polluting energy per year- enough to power about 35 Norwegian homes (70 U.S homes
CONCLUSION
Ocean energy can play a significant role in our nation’s renewable energy portfolio. With the right support, the ocean energy industry can be competitive internationally. With the right encouragement, ocean renewable energy technologies can help us reduce our reliance on foreign oil – fossil fuels, in general – and provide clean energy alternatives to conventional power generating systems. And with the right public awareness, our coastline communities can use ocean renewables as a springboard for coastal planning that reflects the principles of marine biodiversity.
In conclusion, we believe that the intense and predictable marine current resource offers the possibility of clean energy at a cost that will ultimately be competitive not only with the other renewables, but in the long run we believe we can compete head on with most forms of fossil fuelled power generation at present-day costs. We think that, given appropriate government support to help the technology through its early and immature stages, it can play a significant role in producing clean energy.
Tidal energy has potential to become a viable option for large scale, base load generation in Scotland. Tidal Streams are the most attractive method, having reduced environmental and ecological impacts and being cheaper and quicker installe