A NOVEL machine that generates electricity from marine tides will be put to the test off the Scottish coast next year. Called the Snail, it uses the flow of water over wings to anchor it to the seabed. This will allow it to operate at a greater range of sites than rival models, its designers say.

Tidal flows have the potential to supply large quantities of renewable energy. But the few large-scale generators currently in operation create environmental problems that have prevented the technique from becoming popular. They work by forcing the tidal flow of water in shallow estuaries through narrow channels containing a turbine, but this can disrupt the tidal ecosystem.

Turbines in deeper coastal waters are a different story: they can exploit a tidal flow without significantly changing it. The sea around Scotland alone could generate up to 16 gigawatts of electrical power, an output equivalent to that ...