Waves and tides in the oceans keep the water continually in motion, and this motion may be used to generate electricity. The wind-generated waves cause the water to oscillate in nearly circular orbits that reach a depth of one-half the wave’s wavelength (the space between peaks). Tides, which are caused by the Moon and Sun’s gravitational pull on the seas, are similar to very long-wavelength waves that, depending on the shoreline’s structure, may create very strong currents in particular coastal places.
Wave and tidal power have a few things in common and a few things in common when it comes to power generation methods. Both terms allude to the process of extracting kinetic energy from the ocean in order to produce electricity (again, by rotating a turbine much as hydroelectric dams or wind farms do), but their locations and power generation methods differ somewhat.
Wave energy projects use the motion of waves that are either on the water’s surface or that are a few tens of meters deeper in the ocean. Technologies for capturing surface wave energy use the kinetic energy of breaking waves to provide periodic impulses that turn a turbine. The US Department of Energy(link is external) provides the following helpful explanation of several surface wave project types:
Oscillating Water Columns: A partially submerged concrete or steel building with a sea entrance below the waterline makes up oscillating water columns. It contains a water column over a column of air. Waves cause the water column to rise and fall when they enter the air column. The air column is compressed and depressurized in turn as a result. Reduced air pressure on the turbine’s ocean side causes air to be sucked back through the turbine as the wave retreats.
Tapchans: Tapchans, also known as tapered channel systems, are reservoirs built on cliffs above sea level that are fed by a tapered channel. The waves become taller as they approach the rock wall due to the canal shrinking. Waves crash against the channel walls and into the reservoir, where they are collected before being pumped via a turbine.
Pendular Devices: Pendular wave-power systems are made of a rectangular box with a sea-facing opening on one end. The motion of the waves causes a flap that is hinged over the aperture to swing back and forth. Both a hydraulic pump and a generator are run by the motion.
Though not too deep, offshore wave energy systems are often installed a few hundred feet below the ocean’s surface. At this depth, the regular wave action is often employed to power a pump that feeds into a turbine, which produces energy.
In order for tidal energy projects to function, water must be forced through a turbine or a “tidal fence” that resembles a row of subway turnstiles. The systems rely on consistent tidal activity to provide electricity. Tidal energy projects have the benefit of being able to supply a reasonably dependable source of electricity since this tidal action is predictable (each coast experiences at least one tidal cycle per day, high tide and low tide, and some regions actually see two tidal cycles on a daily basis). Due to the fact that there are so few locations in the globe that experience sufficiently big tide changes to generate adequate power, as indicated in the chart below, the usage of tidal power has been fairly limited internationally.