Ocean Energy

Ocean Energy is all forms of renewable energy derived from the ocean that is still at an early stage of commercialisation. Wave Energy remains more costly than the other ocean technologies. Tidal range has been deployed in locations globally where there is a strong tidal resource (for example La Rance in France, Sihwa in South Korea), while tidal stream has been demonstrated at pilot scale. There are four main types of ocean technology: Tidal Movement; Wave Motion; Temperature Gradient; Salinity Gradient

Tidal Movement: Potential energy associated with tides can be harnessed by building barrage or other forms of construction across an estuary, while kinetic energy associated with tidal currents can be harnessed using modular systems.

Wave Motion: Kinetic and potential energy associated with ocean waves can be harnessed using modular technologies.

Temperature Gradient: Thermal energy due to the temperature gradient between the sea surface and deepwater can be harnessed using different Ocean Thermal Energy Conversion (OTEC) processes.

Salinity Gradient: At the mouth of rivers where fresh water mixes with salt water, energy associated with the salinity gradient can be harnessed using pressure-retarded reverse osmosis process and associated conversion technologies.

Tidal Energy (or Tidal Power) is a form of hydropower that converts the energy of the tides into electricity or other useful forms of energy. The Tidal Energy is the power available from the rise and fall of ocean tides on the principal of a dam or barrage that captures water in a basin at the peak of a tidal flow, then directs the water through a hydroelectric turbine as the tide ebbs.

Wave Energy (or Wave Power) is the energy produced in the motion of ocean waves to energy that is the concept of capturing and converting the energy from wind force waves on ocean surface water to electricity generation. The Wave Energy (or Wave Power) is the renewable energy, used for electricity generation, water desalination, and pumping of water, etc. The process of the wave energy generation is: Wave Capture (convert the wave motion into usable energy); Wave Conversion (mechanical motion is converted into mechanical energy); Power Generation (converts the mechanical energy into electrical energy). 

Ocean Thermal Energy Conversion (OTEC) is the process or technologies that produces energy from temperature differences in ocean waters.

The theoretical resource potential of ocean energy ranges from 20,000 TWh to 80,000 TWh of electricity generation per year, representing 100% to 400% of the current global demand for electricity. Ocean energy technologies are commonly categorised based on the resource utilised to generate energy. Tidal stream and wave energy converters are the most widely developed technologies across geographies. Other ocean energy technologies that harness energy from the differences in temperature (Ocean Thermal Energy Conversion) and from the differences in salinity (Salinity Gradient) may become increasingly relevant over longer time horizons.

The current global cumulative installed capacity across all ocean energy technologies is 535 MW. As previously mentioned, most of this installed capacity (522 MW) corresponds to a few tidal range projects. Excluding those two projects, the global ocean energy cumulative installed capacity sums up to just around 13.2 MW as of today.

Source: https://energypost.eu

Tidal technology

The theoretical electricity generation potential of tidal energy is the lowest of all OE technologies, at around with 1,200 TWh/yr. This is due to its very location-specific nature as only some countries can really harness this resource. Interestingly, a sub-category of tidal technology, i.e. tidal range, dominates the current cumulative global installed capacity for ocean energy technologies.

Tidal range technology uses the same principles as hydropower. A dam or barrier traps a large body of water brought in by the tides. The difference between the tide height inside and outside the impounded area allows water to be discharged from one side to the other through turbines inside the structure. Tidal range has a 98% share of global installed tidal capacity at present corresponding to mainly two large installations: a 240 MW plant deployed in France in 1966 and a 254 MW plant in the Republic of Korea from 2011. However, tidal range (also known as tidal barrage) poses different deployment challenges, mainly due to the limited site availability and high capital investment and unclear environmental impacts.

This adds to the reason why tidal range has not continued to grow, and tidal energy is now moving towards other tidal technologies, particularly tidal current technologies with horizontal axis turbines. Whereas a few years ago single tidal turbines had the capacity of only 100 kW, turbines of 1.5 MW have now been successfully deployed and many developers are scaling them up further. Currently 10MW of this technology is installed and running with several of them being a first phase of larger tidal current farm projects, the most advanced one being the Meygen project in Scotland. Another roughly 15MW of tidal current technologies are planned to be deployed this year and this number is expected to exceed 2 GW by 2025.

Wave technology

The theoretical potential of wave energy is 29,500 TWh/yr and can mainly be found between 30⁰ and 60⁰ latitude and in deep water (> 40 metres) locations. Wave energy technologies have not seen a convergence towards one type of design, as has happened for other technologies such as wind energy. Roughly ten different technology types are being pursued, including oscillating water column, oscillating bodies and overtopping devices.

In recent years, despite the absence of a clear technology convergence for wave technologies, many deployments are oscillating bodies, particularly of the point absorber type. In this technology, energy is generated from the movement of a buoy caused by all wave directions relative to the base connection. The technology readiness level (TRL) of wave energy is lower than that of tidal and its deployment is currently restricted to demonstration and pilot projects, with roughly 2.3 MW installed globally. However, like tidal turbines also wave energy devices are rapidly increasing in size and power output and up to 10 MW could be installed within the next 2 years.

Tide is the rise and fall of the sea water level that is created by the gravitational effect of the attraction of the moon and sun on the earth causing cyclical movement of the seas, usually twice in each lunar day at a particular place. The Tide movement can be converted to electricity or other useful forms of power through a hydroelectric turbine as the tide ebbs. (Refer to the Tidal Energy (or Tidal Power))

Wave is to move from side to side with a swaying motion while remaining fixed to one point. Waves are different by frequency, amplitude, wavelength and speed of propagation.

Blast Wave is the increased pressure and flow resulting from the deposition of a large amount of energy that is the overpressure wave traveling outward from an explosion point.

Bureau Ocean Energy Management (BOEM) promotes energy independence, environmental protection and economic development through responsible, science-based management of offshore conventional and renewable energy and marine mineral resources. (Source: www.boem.gov)