tidal power

tidal power. The twice daily ebb and flow of the tides have the potential to provide considerable amounts of renewable energy. The first attempts to harness tidal energy were the tidal mills; the earliest found in Northern Ireland date from the 7th century. The principle is that water is stored behind a barrage during high tide and this drives turbines, both as it flows in during the flood and as it flows out again during the ebb. Tidal power stations are currently operating in Canada, France, Russia, and China. The largest is the one on the Rance estuary in France, which produces 320 megawatts of power. Plans to build one in the Severn Estuary in Britain were shelved because of the environmental issues it raised and the enormous expense of building the barrage. The other difficulty is that tidal power stations generate power during the flow of the tides and not at times of peak demand, a difficulty which can only be resolved if technologies for storing huge quantities of energy can be devised. Smaller-scale technology includes tidal fences that use the tidal flows through narrow channels, and underwater turbines that resemble wind generators and may be useful in remote areas and on islands. See illustration overleaf.

M. V. Angel