Technos émergentes 05/08/2024

Tidal & Ocean Currents Energy

Tidal currents are the result of the ocean water mass response to the interaction between the Moon, the Sun and the Earth. Their magnitude depends on the distance of the Sun and Moon from the Earth.

Tidal energy technologies are the closest-to-market ocean energy solutions.

Tidal and current energy is less susceptible to climate change and can produce energy both day and night.

Tidal currents result from the rise and fall of the tide and are intensified by confinement or seabed bathymetry. They are highly predictable in terms of timing & magnitude. Likewise, ocean currents exist in open oceans and flow regularly in the same direction with low variability. They are due to regional differences in temperature and salinity across the globe and the Coriolis effect due to the rotation of the Earth.

Main Current Tidal & Current Energy Technologies

Most technologies used in the Tidal & Current Energy sector converge on horizontal axis devices, with TRL ranging from 5 to 8

- Horizontal-axis turbine (HAT): The tidal current flows past blades that are attached to a horizontal shaft and cause rotation. This generates power much like a wind turbine, but underwater.

- Enclosed tips: The stream’s velocity is increased by concentrating it in a duct. At the end of the duct, a turbine is located to generate energy.

- Tidal kite: The device attached to the seabed or to a floating platform moves through the tidal stream in an hourglass or linear trajectory. This increases the relative velocity and thus its electricity output.

- Archimedes screw / spiral: The stream passes through the spiral of a helical-shaped impeller. The device starts to rotate, and this is converted into energy.

- Oscillating hydrofoil: The flow lifts an oscillating hydrofoil attached to an arm. The up-and-down movement generates energy by activating a shaft or pistons.

- Vertical-axis turbine (VAT): The currents flow through blades parallel to a rotating shaft. Thus generating power regardless of the direction of the flow, similar to vertical wind turbines.

Future development of innovative tidal energy devices

The development of innovative tidal energy devices will contribute to bigger devices to target strong current locations while new designs will target lower current speed and rivers.

New designs are aimed at lowering LCOE (levelized cost of energy), at easier and cheaper maintenance, decreasing environmental impact. They also aim for reduced impact or interference with marine life & vegetation.

Main pros and cons

Tidal energy velocities are predictable and reliable on a 19-year cycle (long term), allowing easy integration into existing power grids and reducing the need for backup energy sources. Although tidal power is predictable, it doesn’t have constant power production, because tidal production follows the tides that can occur during different hours of the day outside of peak. Therefore it must be combined with a battery storage system).

Tidal energy releases high power output compared to wind power with high efficiency and long lifetime, but at high initial construction costs, as well as high operation and maintenance costs.

Tidal and current energy is less susceptible to climate change and can produce energy both day and night, but there are limited site availabilities – at the moment there are no/rare calls for tenders for tidal energy.

Environmental and social analysis highlights

Very few large-scale prototypes have been tested, and even more rarely at pilot farms. Therefore, existing knowledge on tidal, wave or floating wind technologies is scarce.

Life cycle assessment studies support the potential of tidal energy plants as alternative green energies. Studies have shown environmental impacts would be similar to those of large wind turbine installations. Main environmental impacts from ocean energy devices from a life-cycle perspective are due to materials used, while installation, maintenance and operation do not show significant impacts.

As tidal technologies are underwater and invisible, it is likely that they raise less concerns regarding the landscape, leading to less legal action than offshore wind energy.

However, tidal technologies can meet other forms of resistance from stakeholders involved at the local level. A major controversy concerns the impact of tidal technologies on fishery resources. As the impact of tidal techs on aquatic life and migration of fish is still uncertain especially for large-scale projects, representatives of fishing activities might be very sensitive to the installation of such projects in their fishing zone.

Competition for sea space is increasing as new activities emerge. Spatial planning at the national and local level is a key issue, as well as is targeted cooperation between renewable technologies.

Most demonstration projects are located in the UK, Portugal, France, the Netherlands and Canada

Tidal Energy is a predominantly European industry as ~65% of developers are located in Europe; USA, Europe, China & Korea are the main regions & countries investing in and exploring tidal energy projects.

Read more and discover more innovative sustainable technologies, their advantages and their challenges in ENGIE’s 2024 report on Sustainable Emerging Technologies: