Efficient Green Power - Tidal water energy generation

Tidal Energy Generation

Tidal energy is generated during the inflow and outflow of the tide. The two main principles for generating energy are tides moving in the vertical direction, and tidal motion in the horizontal direction. To capture energy using the vertical method, a basin is filled during high tide, then released through a turbine upon low tide, utilizing the potential energy of the stored water. The horizontal method (tidal stream power) makes use of a tidal stream generator, similar to a wind turbine utilizing the kinetic energy from the dense water.

Tidal Stream Generators
A relatively new technology, generating tidal energy from currents in the same way that wind turbines. The density of water, 832 times greater than the density of air, means that a single generator can provide significant power at low water flow rates (compared to wind speed). Since the power varies depending on the density of medium and the cube of speed, it is easy to see that water speeds of nearly one tenth of the wind speed provide the same power the same size of the turbine system. Tidal movement must be at least 2 knots in order to take advantage of the energy potential. There are four dominant engineering approaches; horizontal and vertical axis turbines, oscillating devices, venturi effect generators. The horizontal axis mounted turbines which look similar to a traditional windmill operating underwater. Vertical axis mounted turbines are an improved helical design, rotating with the water, like a turnstile. Oscillating devices use aerofoil sections that do not rotate, but are instead pushed sideways. Venturi effect tidal generators can be mounted in the horizontal or vertical position and use a shroud to increase flow rate through a turbine. All of these tidal generators have been tested and used for actual production of electricity. These are the preferred methods of tidal electrical generation due to the low costs to develop and implement, and the small environmental impacts associated with hydro-electric generation.

Barrage Tidal Power Generation
Turbines are turned by water flows in and out of the estuary basin, bay, or river through the barrage wall to generate power. These systems are similar to a hydro dam that produces Static Head or pressure head (a height of water pressure). When the water level outside of the basin or lagoon changes relative to the water level inside, the turbines are able to produce power. The Barrage are usually created out of caissons, sluices, embankments, turbines, and ship locks. Sluices, turbines, and ship locks are housed in large concrete blocks called caissons. Basins not sealed by caissons are sealed by embankments.

Tidal power which use sluice gates utilize the flap gate, radial gate, vertical rising gate, and rising sector. Barrage systems usually have high civil infrastructure costs and extensive environmental issues associated with what is basically a dam being placed across a large ecosystem or estuary. There are several types of barrage tidal power generation systems including: ebb generation, flood generation, pumping and a two-basin setup.

Ebb generation (outflow generation) is when the basin is filled through the sluices until high tide. Then the sluice gates are closed and pumping may be used to raise the level of water further. When sea level falls to create a sufficient water drop (head) across the barrage, the turbine gates are opened for turbine generation. Once the head is low, the sluices are opened, turbines disconnected and the basin is filled again. This cycle repeats twice a day during tidal flow. Pumping aids in power generation by raising the power output related to head. The energy to run the pumps in more than returned in the generation process.

Flood generation is the opposite (and less efficient) than ebb generation. The basin is filled through the turbines, during the flooding tide. Because of the difference between the sea side and the basin side of the barrage, the height differential reduces more quickly then in outflow generation, especially noticeable in rivers. Energy barrage's can be configured into a dual basin type, allowing for continuous power generation between the two. One basin is filled at high tide while the other basin is emptied at low tide with energy turbines placed between the two basins. This can be difficult to construct and cost prohibitive due to the the extra length of barrage.

Environmental impacts due to this type of tidal generation is caused not only during the construction and habitat disruption, but also during operation. Turbidity (the amount of matter in suspension in the water) decreases as a result of smaller volume of water being exchanged between the basin and the sea. This lets light from the Sun to penetrate the water further, improving conditions for the phytoplankton. The changes propagate up the food chain, causing a general change in the ecosystem. Fish may move through sluices safely, but when these are closed, fish will seek out turbines and attempt to swim through them. Also, some fish will be unable to escape the water speed near a turbine and will be sucked through. Even with the most fish-friendly turbine design, fish mortality per pass is relatively high (approximately 15%). No alternative passage technologies (fish lifts, fish ladders, etc.) have been effectively developed for tidal barrages, by being too expensive or too selective. Open-Center turbines reduce this problem allowing fish to pass through the open center of the turbine. Barrage's also may accumulate sediments because of the high volume of suspended particulates and turbidity, which reduces the effectiveness of the system, and can damage the estuarine ecosystem.

Very few tidal generators are in operation and tidal current technology is in its infancy. No commercial scale production facilities are in operation and no technology standard has emerged.

Tidal Stream Generator

SeaGen Marine Tidal Energy Generator

Copyright © 2015 EfficientGreenPower.com. All rights reserved.