Introduction of Tidal and Wave energy principles
- 2. TIDAL Tidal Power is the power of electricity generation achieved by capturing the energy contained in moving water mass due to tides Two types of tidal energy can be extracted: kinetic energy of currents between ebbing and surging tides and potential energy from the difference in height between high and low tides. All coastal areas experience high and low tide. If the difference between high and low tides is more than 16 feet, the differences can be used to produce electricity.
- 3. TIDAL There are approximately 40 sites on earth where tidal differences are sufficient Tidal energy is more reliable than wave energy because it based on the moon and we can predict them It is intermittent, generating energy for only 6-12 hours in each 24 hour period, so demand for energy will not always be in line with supply.
- 4. Types of Tidal Energy Kinetic energy from the currents between ebbing and surging tides This form is considered most feasible Potential energy from height differences between high and low tide Density of water is much higher than air, so ocean currents have much more energy than wind currents.
- 5. Barrage or Dam Using a dam to trap water in a basin, and when reaches appropriate height due to high tide, release water to flow through turbines that turn an electric generator. Tidal Fence Turnstiles built between small islands or between mainland and islands. The turnstiles spin due to tidal currents to generate energy. Tidal turbine Look like wind turbines, often arrayed in rows but are under water. Tidal currents spin turbines to create energy
- 6. Like wave energy, tidal energy is used for electricity, with the ultimate goal of connecting to local utility grids. A single 11-meter blade tidal turbine outside of Britain’s Devon coast will be capable of generating300 kW of electricity (enough to power approximately 75 homes)
- 7. 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). In currents of that speed, a 15-meter (49.2-feet) diameter tidal turbine can generate as much energy as a 60-meter (197-feet) diameter wind turbine. Ideal locations for tidal turbine farms are close to shore in water depths of 20–30 meters (65.5–98.5 feet).
- 8. There are different types of turbines that are available for use in a tidal barrage. A bulb turbine is one in which water flows around the turbine. If maintenance is required then the water must be stopped which causes a problem and is time consuming with possible loss of generation. The La Rance tidal plant near St Malo on the Brittany coast in France uses a bulb turbine
- 9. When rim turbines are used, the generator is mounted at right angles to the to the turbine blades, making access easier. But this type of turbine is not suitable for pumping and it is difficult to regulate its performance. One example is the Straflo turbine used at Annapolis Royal in Nova Scotia.
- 10. Tubular turbines have been proposed for the UK’s most promising site, The Severn Estuary, the blades of this turbine are connected to a long shaft and are orientated at an angle so that the generator is sitting on top of the barrage. The environmental and ecological effects of tidal barrages have halted any progress with this technology and there are only a few commercially operating plants in the world, one of these is the La Rance barrage in France.
- 11. Category of generation Ebb generation The basin is filled through the sluices and freewheeling turbines until high tide. Then the sluice gates and turbine gates are closed. They are kept closed until the sea level falls to create sufficient head across the barrage and the turbines generate until the head is again low. Then the sluices are opened, turbines disconnected and the basin is filled again. The cycle repeats itself. Ebb generation (also known as outflow generation) takes its name because generation occurs as the tide ebbs.
- 12. Flood generation The basin is emptied through the sluices and turbines generate at tide flood. This is generally much less efficient than Ebb generation, because the volume contained in the upper half of the basin (which is where Ebb generation operates) is greater than the volume of the lower half (the domain of Flood generation). Two-way generation Generation occurs both as the tide ebbs and floods. This mode is only comparable to Ebb generation at spring tides, and in general is less efficient. Turbines designed to operate in both directions are less efficient.
- 13. Pumping Turbines can be powered in reverse by excess energy in the grid to increase the water level in the basin at high tide (for Ebb generation and two-way generation). This energy is returned during generation. Two-basin schemes With two basins, one is filled at high tide and the other is emptied at low tide. Turbines are placed between the basins. Two-basin schemes offer advantages over normal schemes in that generation time can be adjusted with high flexibility and it is also possible to generate almost continuously. In normal estuarine situations, however, two-basin schemes are very expensive to construct due to the cost of the extra length.
- 15. Wave Energy Wave energy is an irregular and oscillating low frequency energy source that can be converted to a 50 Hertz frequency and can then be added to the electric utility grid. Waves get their energy from the wind, which comes from solar energy. Waves gather, store, and transmit this energy thousands of kilometers with very little loss. Though it varies in intensity, it is available twenty four hours a day all round the year. Wave power is renewable, pollution free and environment friendly. Its net potential is better than wind, solar, small hydro or biomass power. Wave energy technologies rely on the up-and- down motion of waves to generate electricity..
- 16. There are three basic methods for converting wave energy to electricity. Float or buoy systems that use the rise and fall of ocean swells to drive hydraulic pumps. The object can be mounted to a floating raft or to a device fixed on the ocean bed. A series of anchored buoys rise and fall with the wave. The movement is used to run an electrical generator to produce electricity which is then transmitted ashore by underwater power cables.
- 17. Oscillating water column devices in which the in-and- out motion of waves at the shore enters a column and force air to turn a turbine. The column fills with water as the wave rises and empties as it descends. In the process, air inside the column is compressed and heats up, creating energy. This energy is harnessed and sent to shore by electrical cable.
- 18. Tapered channel rely on a shore mounted structure to channel and concentrate the waves driving them into an elevated reservoir. Water flow out of this reservoir is used to generate electricity using standard hydropower technologies.
- 19. The advantages of wave energy are as follows: Because waves originate from storms far out to sea and can travel long distances without significant energy loss, power produced from them is much steadier and more predictable day to day and season to season. Wave energy contains about 1000 times the kinetic energy of wind.
- 20. Unlike wind and solar energy, energy from ocean waves continues to be produced round the clock. Wave power production is much smoother and more consistent than wind or solar resulting in higher overall capacity factors. Wave energy varies as the square of wave height whereas wind power varies with the cube of air speed. Water being 850 times as dense as air, this result in much higher power production from waves averaged over time. Because wave energy needs only 1/200 the land area of wind and requires no access roads, infrastructure costs are less.