As the world looks for cleaner ways to make electricity, attention has turned to the immense power of the tides. Nowhere in Canada is that power greater than in the Bay of Fundy, between Nova Scotia and New Brunswick, where the highest tides on Earth rise and fall as much as sixteen metres twice a day. The idea is not new: a small tidal station opened at Annapolis Royal, Nova Scotia, in 1984. What is new is the scale of the ambition, as engineers now hope to capture a fraction of the water that surges through the bay each day.

Tidal energy holds clear advantages over wind and solar power. Unlike sun and wind, the tides are utterly predictable; their timing can be calculated years in advance, which makes the supply of electricity steady and reliable. Modern underwater turbines sit on the seabed and turn as the current flows past, and they produce no greenhouse gases once installed. Because seawater is far denser than air, a tidal turbine can generate considerable power from a current that would barely move a windmill. These machines are also hidden beneath the surface, so they do not crowd the skyline as wind farms sometimes do.