La Rance tidal power plant in La Rance, France. Tidal and Wave Energy

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1 La Rance tidal power plant in La Rance, France Tidal and Wave Energy

2 Tides Tides are caused by the pull of the moon. Tides involve the rise and fall of sea levels. Around the coast of Ireland, the sea level rises and falls twice daily. Tidal energy can be used to generate electricity. The movement in an out of water can be harnessed by Barrages or Dams.

3 Waves are caused by wind, Waves wind is caused by the uneven heating of the Earths atmosphere and the heat comes from the sun. Wave energy can be used to produce electricity. Irelands location, on the edge of the Atlantic Ocean has some of the best wave-power sites in the world!

4 What is tidal energy? Tidal power facilities harness the energy from the rise and fall of tides. Two types of tidal plant facilities. Tidal barrages Tidal current turbines Ideal sites are located at narrow channels and experience high variation in high and low tides.

5 What is the Tidal force? The tidal force is the vectorial difference between the gravitational force of the Earth and the gravitational force of the Moon.

6 Energy from the moon Tides generated by the combination of the moon and sun s gravitational forces Greatest affect in spring when moon and sun combine forces Bays and inlets amplify the height of the tide In order to be practical for energy production, the height difference needs to be at least 5 meters Only 40 sites around the world of this magnitude Overall potential of 3000 gigawatts from movement of tides

7 What Causes Tides?

8 Tidal power, sometimes called tidal energy, is a form of hydropower that exploits the movement of water caused by tidal currents or the rise and fall in sea levels due to the tides. Although not yet widely used, tidal power has potential for future electricity generation and is more predictable than wind energy and solar power. About tidal power

9 high tide low tide

10 History of Tidal Tidal energy is one of the oldest forms of energy used by humans Dating back to 787 A.D., tide mills were constructed, consisting of a storage pond and a sluice (gate that controls water flow). During the incoming tide (flood), the sluice would open to allow rising waters to fill the storage pond During the outgoing tide (ebb), the stored water would be released over a waterwheel In the early 1960 s, the first commercial scale tidal power plant was built in St. Malo, France, consisting of twenty four 10MW turbines.

11 History of Tidal power stations An early attempt to build a tidal power plant took place at Aber- Wrac'h in the Finistere in 1925, but due to financial problems, it was abandoned in Tidal mills have long existed in areas affected by tides. In Europe, tide mills have been used for over a thousand years, mainly for grinding grains.

12 Tidal Barrages The ocean s tides can be used to accumulate potential energy, which can be converted to mechanical energy by turning a turbine in a manner quite similar to hydropower. As the tides rise and fall daily, basins along the shoreline naturally fill and empty. A complete tidal cycle takes 12.5 hours, so there are two high tides and two low tides a day. Dam-like structures called barrages can be built across the mouths of natural tidal basins with sluice gates. Water can be allowed to rise on one side of the sluice until enough of a hydraulic head is built up to power a turbine. The turbines are designed to work in either direction to maximize the utilization of the changing tide.

13 Tidal Barrages

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15 Rance River Tidal Power Station The first commercial tidal power plant in the world is the La Rance Tidal Barrage in France built in The average tidal range is 28 ft, with a max of 44 ft. The barrage extends 2500 ft across. Produces 5.4 GWh of electricity per year, which is only 18% of the available energy in the basin.

16 Tidal Turbines Efforts are underway to anchor turbines to the ocean floor to harness tidal energy. This concept is proven, and in practice in a handful of locations on a small scale. This form of generation has many advantages over its other tidal energy rivals. The turbines are submerged in the water and are therefore out of sight. They don t pose a problem for navigation and shipping and require the use of much less material in construction. Tidal turbines are vastly better than wind turbines in terms of efficiency. A tidal turbine produces 4 times the output power per square meter of sweep area as a wind turbine, with a substantially smaller environmental impact.

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19 Siemens SeaGen (S) Tidal Turbine

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21 Domestic Tidal Power There are no tidal power stations in the U.S., but plans are underway to build a small tidal power farm in the East River of NYC. 300 underwater turbines On average, 10 MW of power (44GWh of electricity per year, enough for 8000 households) Alaska, Maine, and southeast Canada are potential target areas for barrages.

22 Ocean Thermal Energy Conversion (OTEC) The world s oceans constitute a vast natural reservoir for receiving and storing heat energy from the sun Nearly 75% of the surface area of Earth is water. Due to the high heat capacity of water, the, water near the surface is maintained at significant higher temperatures than water at greater depth It is possible to extract energy from the oceans through the use of heat engines in order to exploit the temperature differences between warm surface water and the cold, deep water

23 How it works First generation, barrage-style tidal power plants Works by building Barrage to contain water after high tide, then water has to pass through a turbine to return to low tide Sites in France (La Rance), Canada (Annapolis), and Russia Future sites possibly on Severn River in England, San Francisco bay, Passamaquoddy

24 Tidal streams Instead of damming estuaries the tidal currents are harnessed using wind like turbines

25 Main methods of current generation Marine current generator Stingray Tidal fence

26 How it works: Tidal Barrages

27 Wave Energy The kinetic energy of moving waves can be used to power a turbine. In this simple example 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 drops, this creates a vacuum in the chamber, causing air to flow in the opposite direction

28 Benefits of Tidal stream Far less intrusive Can generate same amount of power as wind with smaller blades moving slower due to density of water More available sites More reliable than wind Usually less expensive than barrage

29 Benefits Renewable Can help protection of ports in storms Can help navigation for shipping Reliable, more so than solar or wind

30 Advantages Renewable and clean Tides are predictable There is a vast potential for energy generation With tidal turbines, the structures are out of sight Less required material for tidal turbines than wind

31 Environmental factors Change in currents Change in sediments Salinity and quality of water Migratory species

32 disadvantages Presently costly Expensive to build and maintain A 1085MW facility could cost as much as 1.2 billion dollars to construct and run Connection to the grid Technology is not fully developed Barrage style only produces energy for about 10 hours out of the day Barrage style has environmental affects Such as fish and plant migration Silt deposits Local tides change- affects still under study

33 Disadvantages Like wind and solar, tidal power is intermittent In addition, the hydraulic head obtained from tides is also variable Tides do not align with peak energy demand times With regard to barrages, some of the environmental impacts of dams are present with this technology as well, though to a much lower extent VERY, VERY, VERY EXPENSIVE Only produces 1/3 of the electricity that a hydropower plant of equal size would produce Wave power sites produce low energy output

34 Hydropower is an important renewable energy source world wide...

35 Small Francis Turbine & Generator "Water Turbine," Wikipedia.com 35

36 Francis Turbine Grand Coulee Dam "Water Turbine," Wikipedia.com 36

37 Fixed-Pitch Propeller Turbine "Water Turbine," Wikipedia.com 37

38 Kaplan Turbine Schematic "Water Turbine," Wikipedia.com 38

39 Kaplan Turbine Cross Section "Water Turbine," Wikipedia.com 39