by Peter J White

Created on: May 26, 2010   Last Updated: May 27, 2010

What a delicious and amusing irony that man, facing the grim reality of his high-tech fossils fuels winding down to a trickle in about 40 years from now, should discover his deliverance in those same elements that were his inseparable, childhood companions from the beginning: the wind in his hair; the warm friendly sun on his back; and not least the sea on his doorstep.

I would like in this essay, if I may, to examine what might appear at first to be the least likely candidate to support the cause of our redemption before 2050: the seas and oceans which surround every island and continent. 

Generated by the gravitational force of the moon and the rotation of the earth, tides move an immense volume of water twice each day. Converting the energy of this flood into electric power may well provide a substantial, perhaps a major component of the electricity we shall need when the petrol pumps are dry. The more powerful the tide, either in the volume of water or tidal current speed, the greater the potential for electricity generation.

How is it to be done? With commendable courage and foresight the French Government built the world's first tidal barrage as early as 1966, across the River Rance estuary in Brittany.

A barrage is, in effect, a hydro electric dam wall containing powerful turbines, which is filled every day by the tide. It may generate power from the incoming flood tide; at low tide as the water is automatically released; or from both.

A wide concrete built barrage has the advantage that a road, or railway track can be built on top of the wall. The Rance Tidal Power Station, 750 metres long, has so far generated 26400 GW of power and has recovered its capital cost. The maintenance cost of electricity now produced is said to be US$0.18c per kWh, compared with 2.5c per kWh for a nuclear power plant.

There is a ship lock at one end of the barrage with a drawbridge where a road crosses the river, that can be raised to allow larger vessels to pass. 16,000 vessels per annum can commute between the Atlantic ocean and urban centres upstream. 

Not far from Brittany, across the English Channel in the South West of Britain is the broad Severn River estuary flowing into the Bristol Channel, shipping artery for the seaport and harbour of Bristol.

Ever since the 19th century, engineers have relished the thrilling possibility of a barrage across the Severn as a means of linking England and Wales; as flood protection; harbour creation; and especially in recent

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