The seas and oceans represent more than 70 % of the earth's surface. This is a gigantic manna of energy that is not yet really exploited. A green, perfectly renewable energy that could produce a significant part of the world's electricity consumption. This is a colossal challenge that drives innovators to be more imaginative. Numerous building sites, projects and certain achievements exist. But we are still far from the mark. Difficulties are accumulating in the face of oceans that are not so easily tamed.
A clean, renewable energy that does not produce waste and whose production is quantifiable and predictable: the Rance tidal power plant, between Saint-Malo and Dinard, has been combining these assets for 50 years. But this pioneering model, designed to produce electricity from the force of the tides, has never been reproduced in France and relatively few around the world. Only a few rare similar works have since seen the light of day, including the most important one in the South Korean bay of Siwha.
The strength of the tides in question
Inaugurated in 1966, the 240 megawatt (MW) plant produces enough electricity (500 GWh) to supply 250,000 homes. Everything looks perfect on paper, but there's a catch. Its 750-metre long and 33-metre wide dam blocks the mouth of the Rance River. « Exchanges between the estuary and the marine environment have been completely blocked, which has had an enormous environmental impact. ", Antoine Carlier, a marine ecologist at Ifremer, told AFP.
Certainly, for the past fifty years, " studies have shown that biodiversity has returned, but estuarine environments are still fragile, and today it would be very difficult to carry out work in them ", underlines Yann-Hervé De Roeck, Managing Director of France Énergies Marines (FEM).
However, the idea of generating electricity from tides, now a mature technology, has not been abandoned and new projects are emerging, including the creation of tidal lagoons outside estuarine areas. « There, the ecological risk is less ", underlines Antoine Carlier.
In a report entitled "New Tidal Power", released in early 2019 by the Société hydrotechnique de France (SHF), tidal power is considered to be "a new form of energy that can be harnessed to meet the needs of the future". a major asset for the energy transition ». The scientific organisation dedicated to hydraulic research estimates the technical potential exploitable in the world at 1,250 TWh/year, whereas the current effective production is only 1TWh/year, i.e. 0.2% of the annual French electricity consumption.
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Tidal turbines: can do better
Among other marine energies, tidal turbines, these underwater turbines driven by marine currents, also struggle to get off the ground despite their advantages: low environmental impact, no visual nuisance, and a substantial deposit of 10 GW in Europe, including between two and three in France.
But the technology is not yet mature. « There are watertightness, corrosion and maintenance problems on these subsea machines, which add to the cost of the projects. ", explains Marc Le Boulluec, Ifremer specialist in the behaviour of structures at sea.
In 2018, Naval Énergies announced that it would stop investing in the sector because this subsidiary of the Naval Group (formerly DNCS) and Bpifrance had received no public support, as the government considered the technology still too expensive. By 2017 Engie and General Electric had already thrown in the towel.
" We wanted to immediately target the areas with the strongest currents and very deep water, and to do that we had to set up gigantic machines... we may have skipped some stages... "says an industry expert, speaking on condition of anonymity. Smaller players such as the Breton Sabella or the Isère-based HydroQuest seem to be doing well by betting on niche markets such as areas not connected to the power grid like certain islands or the river.
Bioinspiration to the rescue
In spite of the technical difficulties, tidal turbines are still a dream come true. Some innovators are inspired by nature to invent new tidal turbines that are more economical, simpler and therefore more efficient. This is the case of EEL Energy which thus develops a new type of tidal turbine, without a propeller, bioinspired by the swimming of certain fish: thanks to an undulating membrane, it can produce electricity from marine or river currents.
It looks like a large fin that mimics the ripples of fish such as eels or rays. This prototype tidal turbine is made of fibreglass, reinforced with epoxy carbon fibres covered with a rubber that resists tears and abrasion and to which marine organisms do not attach. Under the effect of current, the membrane's corrugation is converted directly into electricity by linear electromagnetic converters. The tidal turbine thus automatically orientates itself according to the current and starts up at low fluid speed. According to its designers, it can be installed at shallow depths, close to coasts, but also in rivers.
Other technologies aim to harness the energy of the oceans, from waves and swell (wave power), to the temperature differences between deep and surface waters (ocean thermal energy), to the reaction obtained when fresh and salt water meet (osmotics). They are, however, at even less advanced stages than tidal power. « We remain confident because the energy resource is really very large... "Yann-Hervé De Roeck assures us that global investments in these energies "are not huge" for the moment compared to those that have benefited solar or wind energy...
Wind in the blades
Wind power, and more specifically offshore wind power, could be a solution. The idea of installing giant wind turbines in the open sea seemed obvious: the winds are strong and regular, and the nuisance, especially aesthetic, almost nil. This is why France had planned, when implementing its energy transition, to install 500 to 600 high-powered machines by 2030. In 2015, the "energy transition" law confirmed these objectives and specified that in 2030, 40 % of our electricity should come from renewable energies. Today, the results are disappointing.
Although France has Europe's second largest offshore wind energy field and the first call for tenders for the construction of offshore wind farms dates back to 2011, our country still has no offshore wind turbines in operation, even though there are now more than 4,000 installed in ten European countries. Incomprehensibly, no offshore wind farm is expected to be operational in France before the end of the five-year period in 2022.
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The persistent delay in approving new projects is fuelling speculation that the French government has an ulterior motive for curbing wind power expansion: that of favouring the nuclear industry.
Indeed, the Multi-Year Energy Program concocted by the government anticipates an increase in electricity demand in the medium term. A debatable scenario: the system operator foresees at best a stagnation in demand. On the other hand, this hypothetical increase corresponds well to the government's plan to develop nuclear power: only an increase in electricity demand can justify the construction of new power stations. In his global strategy for the energy transition, President Emmanuel Macron defends "at the same time" the development of renewable energies and the conservation, in the energy mix, of 50 % of nuclear power by 2035.
By hindering, through administrative guerrilla methods, the development of renewable energies in general and marine energies in particular, are we not creating a form of fait accompli that would lead us to resolve to conceive of nuclear power as the only viable solution to the climate risk? A strategy of decay to make people accept what is still for many unacceptable.
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