We’ve all heard of wind and solar renewable energies, but what about harnessing the kinetic power of the sea? Tidal currents and waves are predictable, making them ideal sources of energy. Tidal stream renewable devices harness the energy from the tidal flow to generate electricity, whereas wave renewable devices harness the movement of waves to generate electricity. The electricity is transmitted via underwater cables to the mainland. These devices need to be able to survive in the hostile marine environment, where they are likely to be subjected to storms, chemical corrosion and encrustation from creatures like barnacles. Unlike wind power, tidal stream and wave renewable devices show a wide range of promising structures. The majority of the renewable devices have been deployed in British waters (Scotland mainly), and the rest are planned to be deployed.
Tidal Stream Renewable Devices
Tidal stream devices rely on turbines, which resemble wind turbines though with smaller blades. This is because water has a higher density than air, which means that the blades can be smaller and rotate more slowly, but still generate a significant amount of power.
Below, horizontal turbine devices, whose underwater turbines are driven by the tidal flow.
Below, enclosed tips devices, where the turbine is enclosed in a funnel-like duct that is fixed to the seabed.
Below, an oscillating hydrofoil device, whose ‘flap’ (or hydrofoil) is made to move up and down by the tidal flow.
Below, a tidal kite device, which is tethered to the seabed. The tidal kite has a turbine under its wing, and it swoops in a figure-of-eight path when moved by the tidal flow.
Wave Renewable Devices
Below, attenuator devices. These floating devices are made to bob up and down by the movement of the waves.
Below, surface point absorber devices, which absorb wave energy from all directions.
Below, oscillating wave surge converters, whose flap moves forward and backwards due to wave movement.
Below, an oscillating water column. These devices are shore-based, and enclose a hollow chamber that is partially submerged in the sea. A column of air is enclosed in the chamber, just above the water level. Wave movement causes the water level in the chamber to rise and fall, which compresses and decompresses the air column directly above it respectively. The air in the air column flows to and from the atmosphere via a rotating turbine.
Below, an overtopping device, which channels waves up a ramp into an enclosed resevoir. The water is released back to the sea via a turbine.
Below, a rotating mass device, which is a floating asymmetrical vessel containing an eccentric rotating mass which is moved by waves.
So there you have it – a summary of tidal stream and wave devices that are currently deployed in the marine environment.