Energy From The Oceans

Energy from the Oceans

Ocean Facts • The oceans cover 71 percent of the Earth's surface and contain 97 percent of the Earth's water. Less than 1 percent is fresh water • The highest tides in the world are at the Bay of Fundy. The difference between high and low tide can be 53 feet 6 inches. • Ninety percent of all volcanic activity occurs in the oceans. • A slow cascade of water beneath the Denmark Strait sinks 2.2 miles, more than 3.5 times farther than Venezuela's Angel Falls • Earth's longest mountain range is the Mid-Ocean Ridge. • Canada has the longest coastline of any country, at 56,453 mi.

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Ocean Facts • El Niño, a periodic shift of warm waters from the western to eastern Pacific Ocean, has dramatic effects on climate worldwide. • At the deepest point in the ocean the pressure is more than 8 tons per square inch, or the equivalent of one person trying to support 50 jumbo jets. • At 39 degrees Fahrenheit, the temperature of almost all of the deep ocean is only a few degrees above freezing. • If the ocean's total salt content were dried, it would cover the continents to a depth of 5 feet. • The Antarctic Ice Sheet is almost twice the size of the US

Energy from the Oceans • Ocean Thermal Energy Conversion (OTEC) • Wave Energy • Tidal Energy • Energy from Currents – Oceans and Rivers • Hydropower

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Ocean Thermal Energy Conversion OTEC • Converts solar radiation to electric power • OTEC systems use the ocean's natural thermal temperature differential to drive a power-producing cycle • If temperature between the warm surface water and the cold deep water differs by about 20°C (36°F), an OTEC system can produce a significant amount of power

OTEC • Potential is estimated to be about 1013 watts of baseload power generation

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Closed System

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Open System

OTEC History • 1861 Jacques d'Arsonval, a French physicist, proposed tapping the thermal energy of the ocean. • 1930 Georges Claude built an experimental 22 kW open-cycle OTEC system at Matanzas Bay, Cuba. Failed to achieve positive net energy. • 1974 Natural Energy Laboratory of Hawaii NELHA at Keahole Point on the Kona coast of the island of Hawaii. • 1979 53 kWe plant at NELHA, 15 kWe net. • 1981 Japan 100 kWe plant, net 31.5 kWe. • 1993 NELHA test 50 kWe net plant.

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OTEC • Economics prohibit a permanent, continuously operating OTEC plant • OTEC is promising as an alternative for tropical island communities • OTEC plants in these markets could provide: – Power – Desalinated water – Mariculture products

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Wave Energy • • • •

Oscillating water columns Floats or pitching devices Wave surge or focusing devices High power density

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Oscillating Water Column

Pitching Devices - Pelamis • Ocean Power Delivery Ltd - offshore wave energy converter called Pelamis. • The Pelamis has a similar output to a modern wind turbine. The first prototype has been built and is being tested at the European Marine Energy Centre in Orkney, Scotland • Future `wave farm' projects may consist of an arrangement of interlinked multi-machines connected to shore by a single subsea cable. A typical 30MW installation would occupy a square kilometre of ocean and provide sufficient electricity for 20,000 homes.

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Pelamis

Pelamis

PowerBouy • The rising and falling of the waves off shore causes the buoy to move freely up and down • The resultant mechanical stroking drives the electrical generator • The generated AC power is converted into high voltage DC and transmitted ashore via an underwater power cable

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PowerBouy

OPT power station showing multiple buoys and underwater transmission cable. Inset shows individual PowerBuoy™. A 10-Megawatt OPT power station would occupy only approximately 4 acres of ocean space.

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Tidal Energy

Spring Tide

Neap Tide

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Bay of Fundy – Medium Tide

Bay of Fundy – Low Tide

Three Schemes for Tidal Energy • Barrage or dam - A barrage or dam is used to convert tidal energy into electricity by forcing the water through turbines. The turbines turn an electric generator to produce electricity. • Tidal fence - Tidal fences look like giant turnstiles. They can reach across channels between small islands or across straits between the mainland and an island. The turnstiles spin via tidal currents typical of coastal waters. Some of these currents run at 5–8 knots (5.6–9 miles per hour) and generate as much energy as winds of much higher velocity. • Tidal Turbine - Tidal turbines look like wind turbines. They are arrayed underwater in rows, as in some wind farms. The turbines function best where coastal currents run at between 3.6 and 4.9 knots (4 and 5.5 mph). Ideal locations for tidal turbine farms are close to shore in water depths of 20–30 meters (65.5–98.5 feet).

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Barrage or Dam Involves erecting a dam across the opening to a tidal basin. The dam includes a sluice that is opened to allow the tide to flow into the basin; the sluice is then closed, and as the sea level drops, traditional hydropower technologies can be used to generate electricity from the elevated water in the basin.

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Tidal Energy Uses large turbines similar to windmills that are turned by ocean movements to generate electricity.

Ocean/River Current Energy • Similar principle to tidal turbines • Would set up in environments where flow is constant and large – Gulf Stream – Hudson River

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Hydropower

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Hydropower • Used historically to power waterwheels, mills, etc. • Now almost exclusively for electricity via dam construction • Some countries get almost all their power from hydro: Norway, Nepal, Brazil • 74,000 MWe now installed in US • Percentage in US is declining (Wattage roughly the same)

Hydropower Advantages • • • •

Non-polluting Renewable Low maintenance Reservoirs have multiple functions

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Hydropower Disadvantages • Silting of reservoirs • Loss of free-flowing streams (Salmon in the Northwest) • Changes in habitat and environment • Negative water conservation through evaporation and infiltration • Risk of dam failure – St. Francis Dam, Teton Dam

Teton Dam Failure, 1976

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