Friday, March 11, 2011

The Future of Energy from Tides and Waves

Think about taming the huge ocean powers from tides and waves to produce a clean endless energy, water crashes against the steep, rocky cliffs on the western coast of Mainland, the largest of the Orkney Islands north of Scotland. The waves comping from the Atlantic are typically 6 to 10 feet high in the summer. In winter, they can reach 30 feet(about 10 meters). It's a perfect location for the European Marine Energy Center (EMEC), a testing ground for wave and tidal-power installations.

Green Renewable Energy

Ocean-powered generators are simple in theory. Like the common hydroelectric power plants, which are often located in large water dams, marine plants rely on the movement of water - either from strong tidal currents or big waves, to turn a mechanism such as the blades in a turbine, driving a generator to produce electricity. But ocean-power stations must be able to withstand the strong heavy currents and unpredictable weather of the open seas. EMEC will need to ensure the reliability and safety of off-shore installations under such harsh conditions and prove that the projects won't harm the marine ecosystem. To do so, it has started laying down infrastructure for test projects from companies around the world in the waters near Orkney.

Undersea electric cables connect equipment just off the coast of the island of Eday to a substation onshore. The cables carry power from underwater installations that will attempt to use the area's almost 9 mph tidal streams - among the fastest in Europe - to generate electricity. Likewise, cables have been laid from the open waters off Mainland to test harnessing waves. Others Dive In The U.S. lags behind the U.K. in wave and tidal-power technology, with most projects still in the planning stage. To help America catch up, last year the Department of Energy invested more than $17 million to support research on the technologies. Part of that money established the Hawaii National Marine Renewable Energy Center at the University of Hawaii and the Northwest National Marine Energy Center, run jointly by Oregon State University and the University of Washington.

Much like EMEC, the centers will host ocean power prototypes and allow researchers to study the performance and environmental effects of their designs. The DOE is also keeping track of some 70 other wave and tide projects being tested in U.S. waters. Across the pond, the first commercial tidal-power plant, owned by Marine Current Turbines, is already operating in Northern Ireland. With the U.S. increasingly focused on eco-friendly energy and the European Union committed to drawing20 percent of its energy from renewable sources by 2020, ocean-based power plants have the potential to be the next big thing in alternative energy. And although there's still along way to go—wave and tidal power lags about 20 years behind wind,and no one is quite sure which of the proposed designs will prevail—researchers are working hard to help ocean power enter the playing field.

The Earth's Tides Explained

The tides are controlled by the gravitational pull of the moon and the sun. The moon is the major player, causing water to collect at the points on the Earth that are closest to it and opposite it. This results in high and low tides approximately two times a day.

Features on the Earth's surface can affect the height and speed of the tides as well. The tides fl ow over an uneven ocean floor and around uneven landmasses, sometimes spreading out over an especially deep or wide body of water and sometimes funneling into especially shallow or constricted areas such as bays, inlets or even rivers. This funneling often causes choppy waves, whirlpools and fast-moving currents—like the nearly 9mph stream at the European Marine Energy Center's Eday test site in the Orkney Islands—as water travels between two landmasses or over a shallow area of the ocean floor. It can also cause a phenomenon known as a tidal bore, in which the incoming high tide creates a wave that travels up and against the usual current of a river or inlet.

Tidal bores can speed along two or three times as fast as the tidal current in open water, sometimes accompanied by high, powerful waves. On the Amazon River, for example, the waves of the tidal bore can reach 12 feet high and are strong enough to dislodge logs along the river's edge. And on China's Fuchun River, waves crest as high as 15 feet, and the current travels up to 15 mph when the tidal bore rolls in.

Energy can be harvested from tidal currents in various ways, from very simple underwater turbines to enormous dam-like projects. Above are four designs for these system

Future Possibility

Wave power has always lagged behind tidal power, which takes advantage of the slightly more predictable nature of currents and has more similarities to wind power.

Wave power suffered a setback in 2008, when a principal investor in a wave farm off the coast of Portugal - the first ever to deliver power to the grid - went bankrupt, forcing the farm to shutdown after just a few months at sea. But supporters of wave power haven't been discouraged. "We learned a huge amount from the Portugal project," says Max Carcas of Pelamis Wave Power, the Scottish company responsible for the design and manufacture of the equipment used at the Portugal farm. "We're keen to move forward," he says.

The company is partnering with the English energy supplier E.ON UK to install and test Pelamis's attenuator-style machines (Below image) at the European Marine Energy Center's Orkney site later this year. And in March, Pelamis announced another energy-company partnership with plans to manufacture and test a second machine at Orkney. Each test-site installation will produce enough electricity to power500 homes. If all goes well there, the company will deploy larger wave farms at other sites around Scotland, ultimately generating enough electricity for 100,000 homes.

More Ways to Trap the Ocean’s Energy

In the future, tides and waves will probably be the most important sources of energy from the seas, but not the only ones. Even though the major oceanic currents usually move far more slowly than tidal currents, they could provide energy. Researchers in Florida are studying whether the energy in the Gulf Stream, which flows along the East Coast,could be tapped. A method known as ocean thermal energy conversion(OTEC) takes advantage of the substantial temperature difference between cold deep-sea water and warm surface water, using both in a process that generates electricity. OTEC systems are being researched at the National Energy Laboratory of Hawaii Authority facility in Kailua. And last November, the European energy company Statkraft opened its prototype osmotic power plant in Tofte, Norway, which harnesses the pressure of saltwater and fresh water mixing through a semipermeable membrane to drive a turbine.

The Need for a Cleaner, Greener and Sustainable Energy

Unlike fossil fuel energy types that use natural sources, renewable energies are known as clean energies. Their production does not involve any oxidation process, preventing the release of more and more carbon dioxide gases in the atmosphere, as in the case of coal energy, nor any hazardous waste or residue as in the case of nuclear power energy. It is estimated that 1-kilowatt home solar system will produce enough energy to save 170 lbs of coal being burned and 300 lbs of carbon dioxide being added to Earth's atmosphere. These clean energy sources will also help decrease the amount of green house emissions due to conventional energy production.

The sustainability quality comes from two features of renewable energy: their source is renewable, therefore it will not be affected from any supply shocks like oil, and lower production costs and the potential of future technological improvements promise clean, renewable energy that is also cost efficient in the long run. The latest trends show higher inflows of private capital into solar and wind energy. Alternative energy has also proven to be better for developing countries where delivery and production of energy may be done through less efficient methods. Kenya is the currently the developing country with the highest increase in solar panels per capita; people who use them become less dependent on the country's central energy supply, hence less costs on the long term for both the users and the energy industry.

Source: Science Illustrated and Sources.

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