Ocean & Tidal Energy

With the oceans covering over 70% of the earth’s surface, they are the world’s largest collector and retainer of the sun’s vast energy – and the largest powerhouse in the world. Jacques Cousteau said it was equivalent to 16,000 nuclear plants. This energy is continually renewed and is available 24/7.Just a small portion of the energy conveniently stored in the oceans could power the world.

For over 60 years, several forms of tapping energy from the ocean have been researched and implemented, and now with fossil fuels running out and becoming increasingly expensive, they are more than competitive in costs – and the ‘fuel’ from the ocean is both free and clean.

The massive oceanic surface currents of the world are untapped reservoirs of energy. Their total energy flux has been estimated at 2.8 ¥ 1014 (280 trillion) watt-hours. Because of their link to winds and surface heating processes, the ocean currents are considered as indirect sources of solar energy. If the total energy of a current was removed by conversion to electric power, that current would cease to exist; but only a small portion of any ocean current’s energy can be harnessed, owing to the current’s size.

One of the primary advantages of this technology is the energy density. While solar and wind systems are well-suited for remote off grid locations, ocean energy is ideal for large-scale developments in the multiple gigawatt range. Sea water is 832 times as dense as air, providing a 5 knot ocean current with more kinetic energy than a 350 km/h wind.

Ocean currents are one of the largest untapped renewable energy resource on the planet. Preliminary surveys show a global potential of over 450,000 MW, representing a market of more than US$550 billion.
Areas that typically experience high marine current flows are in narrow straits, between islands and around headlands. Entrances to lochs, bays and large harbours often also have high marine current flows (EECA,1996). Generally the resource is largest where the water depth is relatively shallow and a good tidal range exists. In particular, large marine current flows exist where there is a significant phase difference between the tides that flow on either side of large islands.

Electricity also can be generated by tidal water flowing both into and out of a bay. As there are two high and two low tides each day, electrical generation from tidal power plants is characterized by periods of maximum generation every twelve hours, with no electricity generation at the six hour mark in between. Alternatively, the turbines can be used as pumps to pump extra water into the basin behind the barrage during periods of low electricity demand. This water can then be released when demand on the system is greatest, thus allowing the tidal plant to function with some of the characteristics of a “pumped storage” hydroelectric facility.

  • Wave energy contains roughly 1000 times the kinetic energy of wind, allowing much smaller and less conspicuous devices to produce the same amount of power in a fraction of the space
  • Wave energy varies as the square of wave height, whereas wind power varies with the cube of air speed. Water being 850 times as dense as air, this results in much higher power production from waves averaged over time
  • Because wave energy needs only 1/200 the land area of wind and requires no access roads, infrastructure costs are less

Source: Ocean Energy Council