Energy alternatives : Ocean Energy

The oceans offer two sorts of available kinetic energy — that of the tides and that of the waves. Neither currently makes a significant contribution to world electricity generation, but this has not stopped enthusiasts from developing schemes to make use of them. There are undoubtedly some places where, thanks to peculiarities of geography, tides offer a powerful resource. In some situations that potential would best be harnessed by a barrage that creates a reservoir not unlike that of a hydroelectric dam, except that it is refilled regularly by the pull of the Moon and the Sun, rather than being topped up slowly by the runoff of falling rain. But although there are various schemes for tidal barrages under discussion — most notably the Severn Barrage between England and Wales, which proponents claim could offer as much as 8 GW — the plant on the Rance estuary in Brittany, rated at 240 MW, remains the world's largest tidal-power plant more than 40 years after it came into use.

There are also locations well suited to tidal-stream systems — submerged turbines that spin in the flowing tide like windmills in the air. The 1.2 MW turbine installed this summer in the mouth of Strangford Lough, Northern Ireland, is the largest such system so far installed.

Most technologies for capturing wave power remain firmly in the testing phase. Individual companies are working through an array of potential designs, including machines that undulate on waves like a snake, bob up and down as water passes over them, or nestle on the coastline to be regularly overtopped by waves that power turbines as the water drains off. The European Marine Energy Centre's test bed off the United Kingdom's Orkney Islands, where manufacturers can hook up prototypes to a marine electricity grid and test how well they withstand the pounding waves, is a leading centre of research. Pelamis Wave Power, a company based in Edinburgh, UK, for instance, has moved from testing there to installing three machines off the coast of Portugal, which together will eventually generate 2.25 MW.