Ocean power is sustainable energy generated by converting the ocean’s waves, tides, currents, and thermal variations into electricity using turbines, generators, and other standard power generating equipment. Ocean power is widely promoted as a cost-effective and environmentally responsible alternative to energy produced by burning fossil fuels such as petroleum and coal. World-wide, 20,000–80,000 terawatt-hours per year (TWh/y) of electricity could potentially be generated combining all currently available technologies that capture ocean energy.
A Short History Of Ocean Energy
The earliest known mechanical conversion of wave power comes from Napoleonic Paris in 1799, when inventor Simon Girard filed a French patent application for using ocean waves was an energy source. However it wasn’t until the late 1800s that mass adoption began and multiple “wave motors” started dotting the California coast.
What Are The Sources Of Ocean Power?
Ocean power is generated by harnessing the ocean’s waves, tides, currents, and thermal variations.
Wave energy forms when the wind blows over the surface area of the sea. The waves continue to build energy and become larger the harder the wind blows and the more distance they have to travel. The resulting energy can be harnessed using a Wave Energy Converter to perform mechanical work, such as desalinization or pumping water, and can be converted into electricity for general use.
Tidal energy is generated by the gravitational pull of the Sun and the Moon. As the Earth rotates and its moon orbits, a tidal bulge of ocean water forms. The tides move in a consistently calculable manner, the magnitude of which is determined by the relative positions of the Sun and Moon. The resulting energy can be harnessed mechanically to perform work, such as turning waterwheels or mill grinding, or by using various methods to convert it into electricity.
Current energy is created by many forces, including breaking waves, the wind, the Coriolis effect of the Earth’s rotation, cabling, and variations in temperature and salinity. These forces cause the continuous directed movement of sea water, and control its direction and strength. The resulting energy can be exploited mechanically by seafaring vessels to build and maintain speed, or can be converted into electricity by harnessing its kinetic motion.
Thermal energy is generated by the difference in temperature between sunlight-heated surface water and cooler water at depth where sunlight cannot penetrate.
How Is Ocean Power Converted Into Electricity?
Wave energy is converted into electricity using four common methods, which are categorized by the manner in which they capture wave energy. However, the underlying principle common to all is that they capture the oscillating kinetic energy of a passing wave and convert it to electricity. Point absorber buoys use the rise and fall of swells to activate an electricity generating hydraulic pump. Surface attenuators similarly channel the motion of swells, but use flexible arms to drive electricity generating hydraulic pumps. Oscillating water columns use swells to compress the air in an integrated chamber to drive an electricity generating air turbine. Overtopping devices ride the swells as long tubular structures, converting potential energy to electricity using low-head turbines. Although Wave Energy Converters have not yet attained commercial viability, developers have reached significant milestones and are now progressing from launching single unit prototypes to large array deployment projected to deliver megawatts of marine-sourced electricity.
Tidal energy is converted into electricity using two common methods, both of which are categorized by the manner in which they channel tidal motion. However, the underlying common principle is that they capture the kinetic energy of moving water and convert it into electricity. Tidal stream generators use the ebb and flow of a tide to turn an electricity generating turbine. Tidal barrages operate like hydroelectric dams, storing and using falling water to spin electricity generating turbines. The only difference being that the source water is replenished by the tides instead of water cycle precipitation. The largest tidal power project currently in operation is MyGen in Scotland, which generates 398MW.
Current energy is converted into electricity using two common methods, both of which are categorized by the manner in which they harness water flow. However, both methods achieve their energy extraction goal by converting a current’s kinetic motion. Axial-flow horizontal-axis propellers are anchored to the sea bed and use current flow to spin an electricity generating water turbine, much like a wind turbine captures the wind. Cross-flow Darrieus rotors are also anchored to the sea floor, but engage the current using a rotating rotor, similar to an underwater waterwheel. Current Energy Converters have not yet attained commercial viability and are still in the development stage. However, research is ongoing and ocean currents off the coasts of Japan, Florida and Hawaii are being considered for marine power generation.