Harvesting green tidal energy

August 6, 2012 by  
Filed under Green Energy News

Dhaka, Aug. 5 — Ocean power is an endless source of renewable green energy. It is clean, environmentally acceptable and economically cheap. Electricity generation from ocean energy is based on tidal power, wave power, ocean thermal energy conversion, ocean winds and salinity gradients. Among these, three well developed technologies are tidal power, wave power and ocean thermal energy conversion. Tidal energy is a form of hydropower that converts the tidal energy into electricity. It requires large tidal differences. This difference between the mean high-water volume and the mean low-water volume of an estuary is called tidal prism. The term ‘tidal prism’ can be defined as the total amount of water that flows into a harbor or flows out again with movement of the tide in water flow. Tidal energy has been used since the ,Roman times and in the middle Ages in Europe to run early tide mills. No doubt, this energy is pollution free and environment friendly. Therefore, world must think to replace fossil fuel based energy by this green energy.

In the present time, a number of countries have already been. using tidal power to generate electricity. World’s largest plant for the generation of electricity from tidal energy is in La Rancee in France. A number of tidal energy based power stations have been established in North America. India has planned to generate electricity from tidal energy very soon. Bangladesh has to think about this to overcome its present electricity crisis and the future energy security. The position and shape of Bangladeshi coast and its islands are favorable for the establishment of tide based power station.

Tides result from the gravitational attraction of the Earth-Moon-Sun system acting on the earth’s ocean. Tides are long period waves that result in the cyclical that generate electricity from horizontally flowing tidal currents like wind turbines. Tidal energy is predictable than .wind energy and solar energy, but cannot be used to generate electricity at consistent level constantly. Twice in every 12.42 hours (24 hours in some locations) the tidal current speed and hence the electricity generation capacity falls to zero. If tidal energy is required to produce a sustained based load for local grid, then some form of energy storage or back-up will be needed.

There are two main types of tidal energy – tidal stream systems and barrages. Tidal stream systems use the kinetic energy of the moving water to power turbines and barrages use the potential energy in the difference between the height of the high and low tides. Barrage systems involve high civil engineering infrastructure costs and environmental issues related to altering the ecosystem.

Due to these reasons, the use of barrage system in the world is limited. In the case of Bangladesh, tidal stream systems will be more suitable and economic. Tidal stream systems are placed where the currents are strong and fast. Good locations .are at the entrances to bays and rivers and between islands or other land masses where the currents become concentrated forces. There are a number of designs for tidal stream systems.

Bangladesh is a low lying country. The mighty Bay of Bengal is situated in its south. High and low tides in this bay are natural phenomena. Tides effect up to Aricha Ghat as well as the confluence of the Jamuna and the Gangase rivers and in the Surma River up to Sylhet City and haor basins. The Meghna River estuary is funnel shaped and the Bay of Bengal is open to the Indian Ocean.

The river systems of Bangladesh carry 1,100 million acre feet (l acre foot = 1233.48 cubic metre) of water annually and a sediment load of 2.4 billion tons per year. This fresh water and sediments load are being poured in the great Bengal Fan in the Indian Ocean. If it is not so, the delta would grow rapidly and the coast of Bangladesh did proceed further south more rapidly. In the present situation, the shape of the coast and the position of its islands open some effective channels. These channels are very much suitable to place tidal energy based turbines to generate electricity.

As. mentioned earlier, the Meghna River estuary is funnel shaped and the Bay of Bengal is open to the Indian Ocean. A number of smaller funnel shaped coasts within the main coast and a number of islands nearer these coasts as well. As a result, a number of channels have been created in between these islands and the main coast. Water current during high and low tides of these channels are very fast and strong. That is why, these are very much effective and suitable places to establish electricity generating turbines. Jaldi (Norman) and Sandwip channels are two such places of the Bay of Bengal. They are situated near Chittagong-Noakhali coast.

The depth to the sea floor at these channels is around 6.0 metres below sea level and the tidal range at these channels is 5.49 metres. Therefore, these two channels can be selected to establish tidal energy based power stations. Among these two, the Norman channel is narrower, so it is more suitable. Proposed projrft will not hamper sea fishes, especially the hilisha fish. Detailed feasibility study will be required to make final decision. If the channel widths are big, then artificially it has to be reduced if it is required. Water current of narrower channels will be stronger and faster and will be able to generate more electricity.

Considering all the above situations, Bangladesh may proceed to establish tidal energy based turbine to generate electricity using tidal stream system where kinetic energy of high and low tides are moving water. The Norman and Sandwip channels would be the ideal place to place these turbines. In later time, it may search new places and in this age oof satellites, it is easy to identify deeper channels.

Further the country may think about barrage system, where the potential energy of high and low tides water-level elevation exists. Though it involves huge investment, the production of electricity will also be big. In this case tide affected rivers of Bangladesh may be under considerations. Published by HT Syndication with permission from The New Nation. For any query with respect to this article or any other content requirement, please contact Editor at

htsyndication@hindustantimes.com

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