NEW Energy! Tidal Power! by Liora Leah Blog entry

Blog: Mother Earth Heals
by Liora Leah

NEW Energy! Tidal Power!

Tidal energy is an alternative form of power under development--the tides as powered by the moon are predictable. If we can harness the power of the tides, we could have cheap green energy. More Research & Development is needed!

Date: 4/13/2011 1:36:40 PM ( 13 y ) ... viewed 44198 times

http://www.esru.strath.ac.uk/EandE/Web_sites/01-02/RE_info/Tidal%20Power.htm

exerpt from the website:

Introduction

If there is one thing we can safely predict and be sure of on this planet, it is the coming and going of the tide. This gives this form of renewable energy a distinct advantage over other sources that are not as predictable and reliable, such as wind or solar.

The gravitational force of the moon causes the oceans to bulge along an axis pointing directly at the moon. The rotation of the earth causes the rise and fall of the tides.

The rotational period of the moon is around 4 weeks, while one rotation of the earth takes 24 hours; this results in a tidal cycle of around 12.5 hours. This tidal behavior is easily predictable and this means that if harnessed, tidal energy could generate power for defined periods of time. These periods of generation could be used to offset generation from other forms such as fossil or nuclear which have environmental consequences. Although this means that supply will never match demand, offsetting harmful forms of generation is an important starting point for renewable energy.

There are two options for getting energy from the tide, a TIDAL BARRAGE or utilising TIDAL STREAMS.

THE TIDAL BARRAGE is where a dam or barrage is built across an estuary or bay that experiences an adequate tidal range. This tidal range has to be in excess of 5 metres for the barrage to be feasible (http://www.iclei.org ). The purpose of this dam or barrage is to let water flow through it into the basin as the tide comes in. The barrage has gates in it that allow the water to pass through. The gates are closed when the tide has stopped coming in, trapping the water within the basin or estuary and creating a hydrostatic head. As the tide recedes outwith the barrage, gates in the barrage that contain turbines are opened, the hydrostatic head causes the water to come through these gates, driving the turbines and generating power. Power can be generated in both directions through the barrage but this can affect efficiency and the economics of the project.

The barrage will have environmental and ecological impacts not only during construction but will change the area affected forever. Just what these impacts will be is very hard to measure as they are site specific, and each barrage is different.

The change in water level and possible flooding would affect the vegetation around the coast, having an impact on the aquatic and shoreline ecosystems. The quality of the water in the basin or estuary would also be affected, the sediment levels would change, affecting the turbidity of the water and therefore affecting the animals that live in it and depend upon it such as fish and birds. Fish would undoubtedly be affected unless provision was made for them to pass through the barrage without being killed by turbines. All these changes would affect the types of birds that are in the area, as they will migrate to other areas with more favourable conditions for them.

TIDAL STREAMS are fast flowing volumes of water caused by the motion of the tide. These usually occur in shallow a sea where a natural constriction exists which forces the water to speed up. The technology involved is very similar to wind energy, but there are some differences. Water is 800 times denser than air and has a much slower flowrate; this means that the turbine experiences much larger forces and moments. This results in turbines with much smaller diameters. The turbines must either be able to generate power on both ebbs of the tide or be able to withstand the structural strain. This technology is still in its infancy despite the potential for a reliable and predictable source.

Tidal stream technology has the advantage over tidal barrages when you compare environmental and ecological issues. This technology is less intrusive than on and offshore wind, and tidal barrages, any hazard to navigation or shipping would be no more than that experienced by current offshore installations. Tidal Stream systems often have to be installed in difficult coastal waters and the installation and maintenance methods are often complicated, but these hold they key for ensuring the success of the technology.

Energy can be captured from tidal streams using two methods, Tidal fences and Tidal turbines.

Tidal Fences
These are effectively another form of tidal barrage. They therefore share some of the same environmental and social concerns, but also have the advantage of being able to have the electrical generators and transformers above the water. The flowing diagram shows an example of a tidal fence.

Tidal Turbines
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. They are also less harmful to the environment.

One new technology that has been developed is the Stingray. This project has definite potential and planning is underway for a trial in the North of Scotland. For more information see the Stingray Case Study http://www.esru.strath.ac.uk/EandE/Web_sites/01-02/RE_info/tidal1.htm

Tidal stream technology is still in its infancy and therefore there are no comparable projects at the present time. The cost of utilising tidal streams will be very site specific and depend on the technology used. The turbine or other generating plant equipment can be considered to have a similar cost to wind.

Once installed, electricity will be produced with no fuel costs and will be completely predictable. Maintenance costs will be the main costs during the life of the project.

The environmental effects of utilising tidal streams are in no way as severe as those for a tidal barrage. They will obviously affect the seabed where they are positioned and this might have an effect on the aquatic life in the area. This is again site specific and hard to predict; as long as proper environmental impact assessments are done then this can be avoided or minimised.

Tidal energy has potential to become a viable option for large scale, base load generation. Tidal Streams are the most attractive method, having reduced environmental and ecological impacts and being cheaper and quicker installed. The proposed Stingray project is important to demonstrate the potential for the tidal energy industry.

For more information and to view diagrams, go to: http://www.esru.strath.ac.uk/EandE/Web_sites/01-02/RE_info/Tidal%20Power.htm

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