For centuries, coastal communities have watched the tide rise and fall twice daily without considering it a source of power. Tidal energy, once dismissed as too unpredictable for large-scale use, is now among the most promising forms of renewable generation. Unlike wind or solar, tidal cycles are governed by lunar gravity and can be calculated decades in advance.
The first commercial barrage opened in Brittany, France, in 1966. Modern designs differ: underwater turbines, resembling submerged windmills, sit on the seabed and turn with each current. Because water is roughly 800 times denser than air, a tidal stream moving at modest speed carries far more energy than a strong breeze.
Critics point to cost and ecology. Barrages alter estuary habitats and can slow the migration of fish. Turbines still pose collision risks to marine life, and installation in hostile waters remains expensive. Yet as turbine prices fall, analysts predict tidal power could supply a significant share of coastal electricity demand within twenty years.