PARIS SCIENCES & LETTRES (PSL)
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An overview of marine renewable energy

Seas and oceans are endowed with vast reserves of renewable energy. Marine renewable energy takes the form of kinetic energy (winds and currents), potential energy (tidal amplitude), mechanical energy (waves), thermal potential (vertical temperature gradients) or even osmotic pressure (horizontal gradients of salinity). For countries and territories that have extensive maritime areas, renewable marine energy can make a significant contribution to low-carbon electricity production in the energy mix. This is particularly the case with islands that are not interconnected with continental networks, in addition to conventional production.

22
June 2017
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lire en français
Executive Resume

On January 20, 2016, EDF and DCNS immersed the first marine turbine of the future demonstrator marine energy park of Paimpol-Bréhat, off the coasts of Côtes-d’Armor, France. In July 2016, Sabella D10 successfully completed a test year in the Iroise Sea, between the Molène archipelago and the island of Ushant. Marine energy extraction technologies are being tested in a real-world environment and continue to grow – sometimes, with accidents along the way: the Paimpol-Bréhat marine turbines had to be brought back to earth, due to corrosion problems.

At the same time, offshore wind is gradually reaching its maturity, with increasingly powerful turbines and decreasing production costs: in the United Kingdom, the symbolic threshold of 100 pounds/MWh could be reached by 2020.

Over the past decade, marine energies have been on the rise, even if it came late: the first industrial application aiming at exploiting ocean energy, irrespective of the technology, was the tidal power station of Rance (240 MW) which celebrates its fiftieth year of operation in 2017. It provides for 2.5% of Brittany’s annual electricity needs. Until the mid-1990s, it was the only installation in the world to exploit the energy of the oceans in industrial form.

Since then, many progress and investments have been made, especially over the past decade, to achieve significant technological advances. Although globally dynamic, the marine RE sector is heterogeneous: some technologies are close to maturity while others are still in their experimental phase.

Available technologies

Offshore wind. Today, the most dynamic technology on the market is offshore wind. It divides into two main categories: grounded wind turbines and floating wind turbines, which differ mainly by the type of their foundation.

In the first category, the turbine is attached to a support dug into, or placed on, the seabed. Technical and economic constraints limit its deployment to areas with a maximum depth of approximately 50 m, which partly explains its success in shallow seas such as the Baltic or the North Sea. At the end of 2015, the installed production capacity reached 11 GW over 11 countries in Europe.

The second category is used when the depth ranges between 50 to 300 m. The wind turbine is then fixed to a floating support, itself anchored to the seabed. This allows access to a much larger deployment space than in the case of onshore wind. The CAPEX of a floating wind system is estimated at several tens of millions of euros (for a power of 5 to 7 MW).

The technically exploitable potential (TEP) in Europe is estimated at 250 GW and 600 GW, respectively, for grounded and floating wind turbines. In 2016, an additional 1,558 GW increased the installed capacity to 12,631 GW and 3,589 offshore wind turbines. It should be noted that the 2016 figure has significantly decreased compared to the outstanding 2015 year, reflecting the high sensitivity of investment decisions to oil and gas prices.

The two technologies present a very different degree of maturity or, as it is called, Technology Readiness Level (TRL). Offshore wind has reached full maturity and has been marketed for over 25 years (TRL9). The TRL of floating wind turbines varies from 4-5 to 8, depending on the project. In 2016, the WindFloat project (EDP, Principle Power) was a great success. After five years in real operating conditions off the coast of Portugal, the 2 MW wind turbine and its floating base have convincingly proved the viability of this technology.

What about the costs? Currently, the cost of producing offshore wind power in Europe is estimated at around €160/MWh, compared to €70-90/MWh for onshore wind power production.

The case of the United Kingdom, the leading European country in this segment (for geographical reasons but also because of strong political support), shows a downward trend in costs: According to a study by the UK Offshore Renewable Energy Research Center, thanks to strong growth in this market and an increase of turbine power from 2013 to 2015, the cost of MWh produced by offshore wind farms in the United Kingdom has decreased by 11%. Nevertheless, these costs still remain high as for today.

Their CAPEX (capital expenditure) is around €5,200 per installed kilowatt, at the higher end for this type of investment. However, these figures should be put into perspective with two elements: for island territories, transport costs of oil and gas change the economic equation and often justify costly investments; second, the performance of marine wind is more regular than that of terrestrial wind, and the variations in production are easier to predict; the issue of intermittence is therefore much easier to manage. On the other hand, if maintenance raises specific problems that have their cost, offshore wind generates less conflicts with residents, limiting the legal risks and costs of operation.

On some sites, however, neighboring beach resorts have raised concerns about the alteration of landscape. On other sites, there have been serious calls from fishing communities. However, it should be noted that according Danish study published by the National Aquatic Resource Institute (Effect of the Horns Rev. 1 Offshore Wind Farm on Fish Communities. Follow-up Seven Years after Construction), wind turbines are artificial reefs that could have a positive effect on some populations of fish, by increasing their numbers.

Hydroelectric power. The study on the use of tidal currents to produce electricity was launched in 1990, using conversion systems called marine turbines. It is currently believed that this technology is economically viable only if the minimum speed of sea currents during high tide is greater than approximately 2 m/s. Exploitable sites are therefore quite limited geographically (Figure 2), making marine power generation a niche market.

In Europe, the United Kingdom accounts for approximately 60% of the reserves and France for about 20% i.e. a PTE of 9 GW and 3 GW, respectively. Islands or isolated systems, even electric peninsulas, that offer an interesting potential and whose electrical production is dependent on fossil energies, are the primary targets of this technology.

In Metropolitan France, the most interesting marine power generation sites are those of Fromveur, Paimpol-Bréhat and Raz Blanchard.

The Sabella D10 marine turbine, with a capacity of 1 MW, operated on the first site during a probationary year. 70 MWh were produced between June 2015 and June 2016.

Two DCNS/OpenHydro hydroelectric plants were installed on the second site. Thanks to Investissements d’Avenir (French government program of public investments), with a budget of approximately 50 million euros per project, the third site is expected to receive seven DCNS/OpenHydro marine turbines and four General Electric (Alstom) marine turbines operating under pre-commercial conditions (TRL 8-9) starting from 2017. The latter project is the result of a collaboration between university research (ANR HYD2M/PHYSIC/THYMOTE projects), industry and national representatives of EMR (France Energies Marines, French Institute for Marne Energy) to capitalize on the assets of the region for the development of an industrial sector.

The recent withdrawal of GE, who judged this technology not quite ready in terms of maturity revealed the fragility of the sector. However, DCNS decided to speed things up by inviting its partners to invest 150 million more (for 200 million already invested) until the end of 2016, seeking to become the global leader of marine energy. “In ten years, this activity could represent a turnover of 500 million to 1 billion euros,” explained Hervé Guillou, CEO of DCNS, in December 2016. Finally, aside from heavyweights of the sector, there is also some room for innovative outsiders: Sabella, who designed and manufactured the Fromveur hydroelectric, is a local SME supported by BPIFrance.

Wave energy extraction technology. Wave energy extraction technology has been the subject of intensive research since the 1970s, when the oil crisis led to renewed interest in renewable energies. But the underestimation of the aggressiveness of the marine environment and the low maturity of the technology were hardly conducive to its development. Since the mid-2000s, the sector is using this stronger interest in renewable energies and technological advances (new materials, resistance to erosion, calculation capacities) to gain momentum. Numerous concepts have been developed based on various principles of energy conversion: mechanical surface energy (oscillations/undulations), sub-surface energy (movement of water molecules under the effect of the swell), pressure variation at the passage of waves or within chambers. Depending on their operating principle, wave energy extraction solutions can be installed onshore or offshore.

At the moment, even if some systems are already on the market, none have really reached industrial maturity and it is still impossible to predict which technology will gain the upper hand since most prototypes do not exceed TRL 6. However, wave energy extraction represents an important economic potential, with reserves on all continents. In order to be economically viable, the lower limit of the average annual potential expressed in watts per linear meter of wave crest is estimated at between 15 and 25 kW/m.

Technically usable wave power at the global level is estimated at 500 GW, based on a conversion efficiency of 40% (IRENA, 2014). In Europe, the Atlantic coast (Scotland, Ireland, France, Portugal, United Kingdom) has the highest potential for wave energy extraction. France is particularly dynamic in this sector. The École Centrale de Nantes (ECN), for instance, used a 1 km² maritime concession off the coast of Guérande to create an experimental site for wave technologies, the SEM-REV. It has all the necessary onshore and offshore equipment to test systems in operational conditions. The ECN also develops its own wave system.

Ocean thermal energy conversion. Ocean thermal energy conversion uses the temperature difference between deep (typically 1,000 m) and surface seawaters to produce electricity. Since a temperature difference of at least 20°C is necessary to compensate for the operating energy of the plant and with deep waters close to an average 4°C, only intertropical zones can sustain this technology. A small difference in temperature degrades the efficiency of ocean thermal energy and must be compensated by pumping huge volumes of cold water (20 m3/s is a correct order of magnitude).

However, the economic stakes remain very high. On the one hand, for intertropical territories whose electricity production is highly dependent on the supply of fossil fuels; on the other hand, because of the immense potential of electricity production from ocean thermal energy, estimated at 10,000 TWh/year i.e. half of the world’s electricity consumption (IEA-OES study). The main economic obstacle to the development of ocean thermal energy is its very high investment expenditure (CAPEX), associated to a significant risk due to the lack of hindsight in this area. The CAPEX is valued at 20 M€/MW installed, or a production cost of 500 €/MWh. Although high, this cost is likely to diminish based on scale effects and the learning curve with cumulative installed power. It is also close to being competitive given the marginal operating costs of thermal power stations on certain islands.

The keys to development

Leaving aside offshore wind, whose development seems assured, let’s examine alternative technologies that have not reached yet the same level of maturity. They represent more of a potential than a reality, both in terms of technological maturity and of economic interest.

But taking positions today, at a time when competition isn’t as fierce, on what remains of the niche markets – or even on non-existent markets – could prove fruitful in ten or twenty years. This is the challenge faced by industrialists such as DCNS who, in January 2017, joined forces with Bpifrance, Technip and BNP Paribas to create DCNS Energies, with the aim of becoming the global leader in marine renewable energy.

At least two reasons explain this decision. The first is the geographical isolation of a large number of maritime territories that depend today on fossil fuels and for which marine renewable energies will offer an appreciable complement, once they can be implemented at reasonable costs and reliably. We are still far from the mark but this ideal is achievable and the possibility of an oil shock (as a counter-effect of the fall in investments) brings it even closer.

Secondly, the evolution of the electricity mix and the rise in electricity demands. The general rise of renewable energy and its increasing importance in the electric mix, on the one hand, and the development of electric mobility, on the other, place electrical production at the center of the game. While convincing storage solutions are not found, energy production will require a certain degree of diversification. Marine renewables emerge as one of the elements of an increasingly complex production system – one that will also increase the system’s overall reliability. The problem of intermittence can be resolved by the variety of sources and therefore, of rhythms of intermittence. Tidal systems, for instance, will offer unprecedented predictability.

Nevertheless, there are still numerous obstacles to the development of marine renewable energies: financial, technological, legal, environmental, industrial, among many others... These are real because inherent to any emerging activity, and we know how fragile certain experiments can prove when players withdraw. However, marine RE is developed both by governments and industrialists concerned by enhancing their assets and taking strategic positions, either to build industrial sectors or to develop their energy autonomy or, in the case of private players, take a position on segments of the future global energy market.

The example of the United Kingdom is exemplary in this respect, particularly in the field of wind power. France offers another textbook case, with geographical advantages, historical know-how and an ecosystem of innovation that can open up a promising future in this field, provided that the efforts are effectively coordinated.

Thanks to its Atlantic seaboard (tides, currents, winds) and overseas territories with a vast maritime domain, France has one of richest RE resources in the world.

It also has an outstanding industrial fabric and know-how in naval architecture. DCNS, for instance, is a submarine manufacturer that develops technology for floating wind, marine turbines and marine thermal energy (the NEMO project, in reference to the solution devised by Jules Verne in 20,000 Leagues Under the Sea). Smaller structures, such as Sabella, have survived against all odds and are now growing and spreading in the Asian market. Eolfi has become a world leader in floating wind power. Thanks to major shipyards such as Saint-Nazaire and Cherbourg, France has world-class expertise in shipbuilding. The industrial fabric is extremely competitive.

However, financial risks inherent to investment in emerging technologies are high, particularly those relating to the assessment of productivity and the resilience of power generation systems to environmental stresses. Oceanographic databases generated and provided by Ifremer or SHOM, originally for another purpose, could nevertheless be put to remarkable use (IREMARE project) in the production renewable marine energy. The same applies to simulation tools used by the University of Caen but also to those developed by HydrOcean (start-up of the École Centrale de Nantes) or the École des Mines (AeroMines). The resources necessary to exploit the marine environment and reduce risks associated with investments in renewable marine energies are available. They need to be put at the service of this sector, with appropriate support, if need be.

In July 2014, the European Parliament and the Council adopted legislation to create a common framework for the planning of maritime space in Europe. Among other things, they allow to foster synergies between various maritime activities while limiting conflicts, introducing clearer rules, providing better visibility for investors and strengthening coordination between the administrations of each country. The willingness to provide a clear and harmonious regulatory and legal framework is therefore a reality.

Victor Hugo saw a huge and yet wasted power in the oceans. There is still long way to go from theory to practice for this power to unleash its full economic, societal and environmental potential. Marine renewable energy is a recent and fundamentally cross-cutting sector. Faced with an unprecedented situation, its many stakeholders (industrialists, financiers, lawyers, academics, decision makers, environmentalists, professionals/users of maritime space) must invent a way to dialogue, organize and benefit from the complementarity of their know-how and develop marine renewable energies while serving their own interests. This is the crucial coordination task carried out by organizations such as France Energies Marines or Ouest Normandie Énergies Marines, and should be promoted by all players of renewable marine energies.

Jean Dubranna
Research Engineer, Centre observation, impacts, énergie, Mines ParisTech PSL Research University