Ocean energy
Oceans cover more than 70% of the Earth's surface. As the world's largest solar collectors, oceans generate thermal energy from the sun. They also produce mechanical energy from the tides and waves. Even though the sun affects all ocean activity, the gravitational pull of the moon primarily drives the tides, and the wind powers the ocean waves.
Ocean Energy is the world's leading event focusing on renewable and sustainable energy from the oceans and is the primary education platform and networking event for key players in the industry. Attendees will learn of the latest technological advances, investment opportunities, regulatory issues, and planned and implemented projects around the world. Companies that participate include federal regulators, state regulations, utilities, banking institutions, engineering firms, manufacturers, academic institutions, etc.
The world's ocean may eventually provide us with energy to power our homes and businesses. Right now, there are very few ocean energy power plants and most are fairly small. But how can we get energy from the ocean? There are three basic ways to tap the ocean for its energy. We can use the ocean's waves, we can use the ocean's high and low tides, or we can use temperature differences in the water. Let's take a look at each.
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[edit] Different types of ocean energy
The idea is not new. Using the temperature of water to make energy actually dates back to 1881 when a French Engineer by the name of Jacques D'Arsonval first thought of OTEC. The final ocean energy idea uses temperature differences in the ocean. If you ever went swimming in the ocean and dove deep below the surface, you would have noticed that the water gets colder the deeper you go. It's warmer on the surface because sunlight warms the water. But below the surface, the ocean gets very cold. That's why scuba divers wear wet suits when they dive down deep. Their wet suits trapped their body heat to keep them warm.
Power plants can be built that use this difference in temperature to make energy. A difference of at least 38 degrees Fahrenheit is needed between the warmer surface water and the colder deep ocean water.
Another form of ocean energy is called tidal energy. When tides comes into the shore, they can be trapped in reservoirs behind dams. Then when the tide drops, the water behind the dam can be let out just like in a regular hydroelectric power plant. Tidal energy has been used since about the 11th Century, when small dams were built along ocean estuaries and small streams. the tidal water behind these dams was used to turn water wheels to mill grains.
In order for tidal energy to work well, you need large increases in tides. An increase of at least 16 feet between low tide to high tide is needed. There are only a few places where this tide change occurs around the earth. Some power plants are already operating using this idea. One plant in France makes enough energy from tides (240 megawatts) to power 240,000 homes.
This facility is called the La Rance Station in France. It began making electricity in 1966. It produces about one fifth of a regular nuclear or coal-fired power plant. It is more than 10 times the power of the next largest tidal station in the world, the 17 megawatt Canadian Annapolis station.
Kinetic energy (movement) exists in the moving waves of the ocean. That energy can be used to power a turbine. In this simple example, to the right, the wave rises into a chamber. The rising water forces the air out of the chamber. The moving air spins a turbine which can turn a generator. When the wave goes down, air flows through the turbine and back into the chamber through doors that are normally closed.
This is only one type of wave-energy system. Others actually use the up and down motion of the wave to power a piston that moves up and down inside a cylinder. That piston can also turn a generator.
Most wave-energy systems are very small. But, they can be used to power a warning buoy or a small light house.
[edit] Why use ocean current energy?
One of the primary advantages of this technology is the energy density. While solar and wind systems are well-suited for remote off grid locations, ocean energy is ideal for large-scale developments in the multiple gigawatt range. Sea water is 832 times as dense as air, providing a 5 knot ocean current with more kinetic energy than a 350 km/h wind.
According to Devon Girard, The Blue Energy Power System acts as a series of underwater windmills exposed to daily hurricane forces. The tremendous volume and density of ocean currents allows our technology to satisfy large electricity demands efficiently. Ocean currents are one of the largest untapped renewable energy resource on the planet. Preliminary surveys show a global potential of over 450,000 MW, representing a market of more than US$550 billion.
[edit] Where will ocean current energy work?
Areas that typically experience high marine current flows are in narrow straits, between islands and around headlands. Entrances to lochs, bays and large harbours often also have high marine current flows (EECA,1996). Generally the resource is largest where the water depth is relatively shallow and a good tidal range exists. In particular, large marine current flows exist where there is a significant phase difference between the tides that flow on either side of large islands.
There are many sites world-wide with velocities of 5 knots (2.5 m/s) and greater. Countries with an exceptionally high resource include the UK (E&PDC, 1993), Ireland, Italy, the Philippines, Japan and parts of the United States. Few studies have been carried out to determine the total global marine current resource, although it is estimated to exceed 450 GW (Blue Energy, 2000).
In the US, the Florida Current and the Gulf Stream are reasonably swift and continuous currents moving close to shore in areas where there is a demand for power. If ocean currents are developed as energy sources, these currents are among the most likely. But most of the wind-driven oceanic currents generally move too slowly and are found too far from where the power is needed. Here is a map of all major known ocean currents.
[edit] What devices are used in ocean energy conversion?
Harnessing the energy from these open-ocean currents requires the use of turbine-driven generators anchored in place in the current stream. Large turbine blades would be driven by the moving water, just as windmill blades are moved by the wind; these blades could be used to turn the generators and to harness the energy of the water flow.
Another proposal calls for a barge moored in the current stream with a large cable loop to which parachutes are fastened. The cable would be moved along by the current acting against the open parachutes. When the parachutes reached the end of the loop they would turn the corner and be dragged back against the current while closed. The continuous movement of the cable would be used to turn a generator to produce electricity.
Another exciting technology is the rim-driven turbine as exemplified by lorida Hydro Power and Light Company. The opportunities for further discovery and derived benefit from Newtonian and non-Newtonian process fluid mechanics, applied vortex hydrodynamics, and linear implosion technologies has just begun.
[edit] Usage of ocean energy
- Ocean waves could provide an energy-efficient way to desalinate seawater. While conventional purification plants have high energy demands, the rocking motion of floating buoys could be used to drive a pump system for desalination. Scale models are currently being tested in wave tanks although these pump air rather than water. The final versions will be around 10 metres in diameter and 20 metres long. One unit should be able to produce around 2000 cubic metres a day, enough to supply water for more than 20,000 people. However, it is uncertain if a wave-powered desalination system could compete with established desalination plants running on electricity. See here for more information.
- The tidal energy conversion system bioSTREAM™ can provide up to 500kW, 1000kW and 2000kW capacities. The bioSTREAM™ mimics the shape and motion characteristics of Thunniform mode swimming species, such as shark, tuna, and mackerel, but is a fixed device in a moving stream. In this configuration the propulsion mechanism is reversed and the energy in the passing flow is used to drive the device motion against the resisting torque of a electrical generator. Unlike the rotating method, this oscillating endangers sea creatures less — the only possibility of the creatures being harmed is their getting smacked by a device. But, this again is unlikely, as the waves pushing the devices will also be pushing the fish in the same direction.
- The wave energy conversion system bioWAVE™ is based on the swaying motion of sea plants in the presence of ocean wave. The hydrodynamic interaction of the blades with the oscillating flow field is designed for maximum energy absorption. This system has numerous advantages over other wave energy devices. For example, the bioWAVE™ is the only wave energy system that captures a wide swath of incident wave energy without using a large rigid structure. It is also the only such device that absorbs energy over the full water depth and continually self-orients with the wave direction. In extreme wave conditions, including hurricanes, the bioWAVE™ is automatically triggered to cease operating and assume a safe position lying flat against the seabed. Systems are being developed for 500kW, 1000kW and 2000kW capacities to match conditions in various locations. For more information see here
