The two previous topics published in this rubric were about pollutions of the sea not discussed during the United Nations climate change discussions in November 2021 (COP 26) and shadowed by the mainstream press despite their high harmful impact on our future: The invasive sea species, and the pollution by plastic wastes. They are available through the button above. This food for thought continues with the solutions evocated by COP 26 as a substitute for petrol and the new markets that may arise from them. Among them, wind energy is the most promoted by groups of pressure and the mainstream press. As a result, many countries have started massively investing in wind farms inland and at sea. However, the sea also offers possibilities to produce energy by converting the action of waves and tides to electricity. Waves energy and wind farms will be discussed another time. Thus, this presentation focuses only on new concepts of tide turbines. Of course, tide energy can be used only in places where currents sufficiently strong to activate turbines exist. However, it is a predictable source of power, which is not the case with the wind. Note that when the configuration of the seaside allowed for, tides have been used since antiquity to power mills. The procedure used during this time consisted of storing water in a reservoir during the rising tide period and activate the mills' wheels during the lowering tide period. These mills' wheels and the mechanisms that moved the millstones were similar to those used on rivers.

It is currently challenging to say which systems are the most advantageous. Most of them are still at the prototype's stage and will need to be tested and improved to determine their efficiency and desirability. Also, we can see that there is no miracle solution and that some concepts are more adapted to some situations than others. Regarding the economic impact of such systems on the diving and ROVs industry, we need to highlight that manufacturers have designed systems that limit subsea interventions to a minimum. For example, no subsea intervention, apart from the trenching of the electric cable and eventually the UWILD (underwater inspection in lieu of drydock) of the supporting vessel, is required for turbines deployed from barges. However, it is not the case for all projects, and we can expect interventions during the construction of the fields and their exploitation. For this reason, some official reports are in the documents listed below and can be read to make an opinion of this potential market. They can be opened and downloaded by clicking on the titles. Videos are also available to visualize the concepts proposed. - Scientific and technical papers: • Wake effects in tidal current turbine farms. Authors: A J MacLeod, S Barnes, K G Rados Published in 2002 • Modeling the Operation and Maintenance Costs of a Large Scale Tidal Current Turbine Farm. Authors: Ye Li & Keith Florig published in 2006 • Methodology for estimating tidal current energy ressources and power production by tidal stream energy conversion (TISEC) devices. Authors: G. Hagerman, B. Polagye, R. Bedard, M. Previsic Published in 2006 • Economic viability of a simple tidal stream energy capture device Author: Alstom power Limited published in 2007 • 3rd Generation Tidal Turbines: too efficient to ignore? Author: Stuart Ballard Published in 2009 • Ocean Energy Technology Overview Authors: Kari Burman, Andy Walker Published in 2009 • Tidal turbine deployment in the Bristol Channel: a case study Authors: M. Willis, I. Masters, S. Thomas, R. Gallie, & 18 authors Published in 2010 • Ramboll Energy: Tidal turbine foundation optimisation Author: R Sinclair Published in 2011 • Tidal Power: Economic and Technological assessment Author: Tatiana Montllonch Araquistain Published in 2011 • Tidal Power: An Effective Method of Generating Power Authors: Rubayiat Tousif, Buland Taslim Published in 2011 • The development of a vertical axis tidal current turbine Authors: Daniel Brinck, Nicklas Jeremejeff Published in 2013 • Power Limitation Control for a PMSG-Based Marine Current Turbine at High Tidal Speed and Strong Sea State. Authors: Zhibin Zhou, Franck Scuiller, Jean Frédéric Charpentier, Mohamed Benbouzid, and Tianhao Tang Published in 2013 • Marine renewables infrastructure network: Tidal measurement best practice manual. International Renewable Energy Agency: Tidal energy - technology brief Published in 2014 • National Renewable Energy Laboratory: Structural Design of a Horizontal-Axis Tidal Current Turbine Composite Blade. Authors: M. J. Lawson, Y. Li Published in 2014 • Tidal Current Turbine and Related Development Problems for Indonesia Author: Dr. Ir. Darmawi Published in 2014 • DNVGL-SE-0163 / Edition October 2015 - Certification of tidal turbines and arrays • Tidal energy from the Severn estuary, UK Author: Chris Binnie Published in 2015 • Tidal Stream Turbine- Introduction, current and future Tidal power stations Authors: Purvi Chauhan, Pathik Patel, Saurin Sheth Published in 2015 • Current tidal power technologies and their suitability for applications in coastal and marine areas Authors: A. Roberts, B. Thomas, P. Sewell, Z. Khan, & 2 authors. Published in 2015 • National Renewable Energy Laboratory: Power Generation for River and Tidal Generators Authors: Eduard Muljadi, Alan Wright, Vahan Gevorgian Published in 2016 • Tidal energy: A review Authors: Vikas M, Subba Rao, Jaya Kumar Seelam Published in 2016 • Experimental Studies of Turbulent Intensity around a Tidal Turbine Support Structure Authors: Stuart Walker, Lorenzo Cappietti Published in 2017 • Ocean Energy Key trends and statistics 2018 Authors: Rémi Collombet Published in 2018 • Orbital Marine Power: Orbital O2 2MW Tidal Turbine - Project Information Summary Published in 2018 • A review on tidal power utilization and operation optimization Authors: Z J Wang, Z W Wang Published in 2019 • A review of tidal current turbine technology: present and future Authors: Faisal Wani, Henk Polinder Published in 2020 • Orbital Marine Power: Orbital O2.2 Tidal Turbine - Project Information Document Author: James Murray Published in 2021 - Videos and animations • “Simec Atlantis Energy”: Marine Current turbine concept • “Openhydro tidal: turbine concept • “Tidal energy” tidal turbine concept • “Orbital marine” tidal turbine concept • “Andritz Hydro” tidal turbine concept • EDF: How a marine turbine works • Minestro tidal system • VOITH tidal system presentation

Note that a few electricity production tidal power plants that use the same principle as mills have been built. However, their turbines can also work when the tide rises and fills the water reserve, making their exploitation less cyclic as antique mills. The largest unit is the Sihwa Lake tidal power station in South Korea (completed in 2011), and the 2nd in size is situated on the estuary of Rance river in France (completed in 1968). However, because they consist of a dam that closes off the estuary on which they are built, these power plants may pose environmental problems. It is, for example, the case of the unit built on the Rance river that provokes an unexpected acceleration of the silting up of the river. Based on such experiences, it seems that the current trend is not to build such massive units but to install more flexible systems. Some of these new systems consist of one or two turbines installed on large piles in the middle of estuaries. These turbines are lowered in the water along the piles to their operational depth and raised above the surface by the opposite maneuver for their maintenance. It is the proposal of companies such as SIMEC Atlantis Energy (see the picture below).

Some other systems consist of installing the tidal turbines on a specific vessel or a barge and anchoring it in an estuary or an area where a strong current is present. It is, for example, the system proposed by “Orbital Marine” (see the picture below). Like the previous design, the turbines can be raised to the surface for maintenance.

Many projects are based on turbines laid on the seabed. It can be annular units with an open centre such as the model in the picture below, designed by “open Hydro” (this company has disappeared).

It can also be open propellers positioned individually or groupped such as in the picture below from Andritz Hydro.

The systems above use blades that can be reversed, such as the variable pitch systems of vessels’ propellers. So these turbines can operate when the direction of the tide change. Other models such as those in the picture below, designed by “Tidal energy” pivot on their axle

Another system, from Minesto’s Deep Green technology, generates electricity from low-flow tidal streams and ocean currents by a wing that uses the hydrodynamic lift force created by the underwater current to move the kite (See the picture below). With an onboard control system and rudders, the kite is autonomously steered in a pre-determined figure of eight, pushing the turbine through the water. By doing so, the turbine experiences water flow several times higher than the actual stream speed and thus produces electricity.

About tidal turbines (February 2022)