France has set ambitious targets for decarbonisation of its economy and reindustrialisation, in order to increase the share of electricity to more than 50 per cent in its energy mix by 2050. This makes it imperative to strengthen the country’s electricity transmission network. France’s transmission system operator (TSO), Réseau de Transport d’Électricité (RTE) is, therefore, proposing a prioritised, optimised and time-phased strategy to successfully complete the transformation of high and very high voltage network over the next 15 years. This will be the third major overhaul of the French electricity system (after the reconstruction of the country post the Second World War and the construction of the electro-nuclear park in the 1980s). In line with the growing renewable energy and the expected consumption growth, European regulations are being implemented as they are vital to achieving carbon neutrality.
In mid-February 2025, RTE published the Schéma Décennalde Développement du Réseau (SDDR) 2025 guidelines, which marks the second phase of public consultation in formulating a 10-year network development plan. Earlier in March 2024, the TSO released its draft SDDR 2024, proposing an investment of around EUR100 billion between 2025 and 2040 to adapt the French transmission network to the energy policy objectives. A lot of developments have taken place since the previous edition of RTE’s SDDR in 2019, viz., the country having redefined the direction of its energy policy, (relaunch of nuclear power, acceleration of renewables with an emphasis on offshore wind [OSW] and solar power, and priority to reindustrialisation via the development of areas of low-carbon industries). Hence, the draft SDDR 2024 presented the network’s development needs to support the new French and the European Union’s policy objectives, reflected particularly in the green, nuclear and renewable industry laws and in the draft French energy and climate strategy, published in November 2023.
The latest guidelines proposed by RTE are based on the results of the technical work and public consultation. RTE has made public a press conference presentation, a summary of the network plan, documents containing feedback from the public, an international comparison of the investment plans and associated practical sheets, along with the progress report of the past five years. It presents the main strategic orientations of SDDR. “This plan is, first and foremost, a genuine national development and equipment plan, which concerns all the regions. But it is also an industrial and sovereign act because the transformation of the network must be synonymous with the economic growth and jobs in France and Europe”, says Xavier Piechaczyk, Chairman of the Board of Directors, RTE.
The SDDR 2025 includes technical, economic and environmental analyses. It also identifies how the different scenarios and rates proposed for infrastructure development impact these parameters. In the latest SDDR, RTE updated the network development plan for five, 10 and 15 years across all industrial components, in a manner consistent with the new context of accelerating the energy transition. The reference strategy proposed by RTE consists of pooling renewables work and climate change adaptation work (two in one). This includes the integration of 18 GW of OSW capacity into the grid by 2035 and 22 GW by 2040 (compared to the current 1.5 GW of installed OSW capacity).“While there has been a strong focus on OSW in the North Sea, we also have the English Channel, the Atlantic and the Mediterranean and we have to make sure that we all go ahead in the same direction to achieve more integration at the European level”, says Matthieu Monnier, Deputy Director, Strategy and Development Offshore Grids, RTE.
The main guidelines of SDDR will be the subject of a public debate, organised under the aegis of the National Commission for Public Debate, and opinions from the government, the Commission de régulation de l’énergie (CRE) and the Environmental Authority. Following these opinions and public participation, RTE will publish a final version of its investment plan for 2040.
Key highlights of the draft SDDR 2025:
Strategic pillars for efficient network
The SDDR is organised around three main axes. The first one is to renew the network and adapt it to climate change. This work represents the main industrial programme of this plan. The electricity transmission network must be partly renewed due to ageing issues as 27 per cent of overhead lines (OHLs) are over 60 years old and 65,000 pylons are between 70 and 105 years old. It must also be adapted to cope with the meteorological consequences of climate change. The network will be adapted to climate change in 2060 (in accordance with the trajectory defined by the government, +4°C in 2100 in France). The SDDR makes it possible to increase the level of adaptation to climate change to 80 per cent by 2040. The SDDR is supplemented by a network operations and maintenance plan adapted to climatic phenomena. In total, by 2040, 23,500 km of lines, 85,000 pylons and the telecom and control system will be renewed throughout the country, in all kinds of environments (mountains, countryside, coastline, urban areas, etc.) for an amount of EUR24 billion.
The second pillar pertains to connecting electricity consumption to successfully electrifying the country and reindustrialising territories and new low-carbon production facilities (renewable and nuclear). The decarbonisation of the existing industry, the reception of new consumers (factories, data centres, electrolysers) and the development of decarbonised means of production (nuclear, OSW and onshore renewables) occupy a major place in the SDDR. The SDDR plans to prioritise network infrastructure that can trigger electrification of the economy. This approach concerns, initially, the industrial port sites of Dunkirk, Le Havre and Fos-sur-Mer, for which the maturity level of the projects is sufficient to trigger investments right away. Additionally, seven economic development zones (Saint-Avold, Sud Alsace, Vallée de la chimie, Plan-de-campagne, Loire-Estuaire, Sud Ile-de-France, Valenciennes) as well as other zones resulting from dialogue with local authorities, are planned, in which work will be launched when the level of commitment of the industrialists is proven. On the electricity production side, the SDDR provides for the connection of future European Pressurised Reactor (EPR) 2, projected for 2040, that of OSW energies, by making provision for the creation of an offshore network that does not exist today, as well as the connection of onshore renewable energies, on the basis of the national objectives. This pillar represents more than half of the necessary investments, that is EUR53 billion, for projects commissioned before 2040.
The third pillar is strengthening the backbone of the high- and very-high voltage network to accommodate larger electricity flows distributed differently across the country, while limiting congestion. By 2040, the challenge is to transfer more electricity through the network, while optimising its operation, in order to avoid congestion that these new flows could generate. To this end, in addition to the work already underway by 2030, RTE has identified five major geographical areas, in the West, East and South of France, in which it will be a priority to strengthen the very-high voltage network between 2030 and 2040. To increase technical capacities of the backbone of the network, RTE is implementing a strategy, which favours the transformation of the existing infrastructure or their doubling, in their current route. New very-high voltage lines outside existing routes will, therefore, be an exception, and will only concern areas that do not currently have them, or where the current network is insufficient. This reinforcement strategy, estimated at EUR16.5 billion, would make it possible to avoid the construction of 30 per cent more OHLs.
A fourth axis concerns the resistance to physical and cyber-attacks and is a matter of national security. However, it is not detailed in the public version of the SDDR.
Industrial strategy and OSW
RTE is promoting the “standardisation, massification, simplification” (SMS) strategy. Under standardisation, RTE proposes to use only two connection structures, one at 320 kV and the other at 525 kV, with a transfer capacity of 1.2 GW and 2 GW respectively. This is estimated to save six months for project commissioning. The massification strategy involves establishing multi-year agreements with suppliers and allocating the targeted GW early on, via global tenders. This will allow RTE a time saving of 9-18 months, in addition to better competitiveness.
Further, the development of the electricity transmission network requires the organisation and mobilisation of an industrial manufacturing base, mainly installed in Europe (cables, offshore stations, transformers, etc.). RTE has already encouraged several suppliers to invest in France. In November 2024, RTE awarded framework agreements to Prysmian, Nexans, NKT Solidal and Hellenic Cables to secure underground cable (UGC) supplies for its projects until 2028. This commitment, worth a total of nearly EUR1 billion, covers the supply and installation of around 5,200 km of UGC for voltage levels ranging from 90 kV to 400 kV. All cables will be produced exclusively in Europe (France, Portugal, Greece, Belgium, Italy, Germany and the Netherlands) for an amount of EUR668 million. In addition to cable production, the commitment includes cable installation and assembly services, valued at around EUR300 million. One-third of the cables will be produced in France at the Prysmian plants in Gron (Yonne) and Montereau-Fault-Yonne (Seine-et-Marne) and at the Nexans plant in Bourg-en-Bresse (Ain). RTE is, thus, reserving almost all the French cable production capacity available until 2028, that is, the production of more than 1,700 km of cables.
In the SDDR, RTE has decided to approach the OSW programme (which involves an investment of EUR37 billion for integrating 22 GW OSW capacity in 2040) from the perspective of industrial control (manufacturing industry and maritime works). The strategy is based on three principles – the first principle is to aim for 50 per cent of the economic benefits of connections in France. This involves establishing long-term strategic partnerships across the entire value chain (platforms, power electronics and cables). These partnerships will be concluded following competitive procedures. For the first high-voltage direct current (HVDC) offshore platforms, Saint-Nazaire shipyards and RTE have concluded such a partnership. As per the contracts awarded in 2024, Chantiers de l’Atlantique will manufacture the first three French offshore platforms and three onshore HVDC converter stations in Saint-Nazaire for the Normandy (Centre Manche 1 and 2) and 1 GW Ile d’Oléron offshore wind farms (OWFs). The projects will be supplied with HVDC systems jointly by Chantiers de l’Atlantique and Hitachi Energy. Furthermore, RTE has launched a call for expressions of interest from equipment manufacturers, with a view to identifying the conditions for the establishment of a submarine cable production plant in France to cover the national needs in particular.
The second principle is to conduct a thorough review of the connection schedule. RTE has implemented a procurement strategy aimed at de-risking the schedule for connecting OWFs. RTE plans to submit a proposed schedule to the government at the end of the ongoing consultation. The third principle is to pay specific attention to the maintenance and renewal of offshore assets. The structuring of the maintenance of these infrastructures must take place by 2030 and it constitutes a challenge for RTE as the operator of this equipment.
Electrification of industry, fuels, reindustrialisation and digital sovereignty
France is in a paradoxical situation. On the one hand, several projects are emerging in the form of creation of new factories, electrification of existing factories, development of low-carbon hydrogen or e-fuel production units or the construction of infrastructures linked to digital sovereignty (data centres and artificial intelligence). More than 140 projects have already signed connection contracts for a cumulative power of 21 GW (more than double the power currently used by industry connected to the transmission network), and requests continue to flow in, particularly for data centres. On the other, the implementation rate is low, with less than 15 per cent of projects confirming their commitment and formally requesting to start work on the network. This raises the question of modalities and timing of the launch of network reinforcements needed to accommodate them. To resolve this, the SDDR defines a new approach to connecting industries to the grid – prioritising all network infrastructures that can trigger electrification of the economy to the extent that manufacturers confirm their commitment to the geographical sites concerned.
Interconnectors
By 2030, France’s exchange capacities will have grown significantly, with an additional 11 GW for export and 9 GW for import. RTE is targeting to complete the commissioning of projects from the last SDDR by 2030, which includes two HVDC connection projects with Spain and Ireland, along with work to increase the exchange capacity at the Spanish, Belgian and German borders. After 2030, any new interconnection project will be conditional on prior strengthening of the internal network; otherwise, either these new interconnections will not be able to be fully exploited, or their use by the market will generate costs for the French consumers.
International comparison of investment plans
In a bid to provide the public with an overall perspective, RTE commissioned Compass Lexecon, a global economic consulting firm to analyse and put into perspective the transmission development strategies of six transmission companies from the Netherlands, Belgium, Germany, Great Britain, Italy and the US state of California vis-à-vis the French strategy as presented in the SDDR 2024.
According to the benchmarking report, the SDDR covers a broader industrial scope than other TSOs, including adaptations and connections, renewal and adaptation to climate change, OSW connection, interconnections and the digital framework. Only the Belgian plan has such a comprehensive scope. The French SDDR integrates the network adaptation to climate change in the network development strategy, while the other plans studied do not cover this issue specifically. Only Italy has made a dedicated investment plan.
Despite a more restricted scope, the German or the British investment plans provide for significantly higher investment amounts than the French plan. For instance, the German plan provides for more than EUR250 billion of investments, against EUR100 billion for RTE over 15 years. These differences must also be put into perspective of the time horizons and voltage levels covered in these plans. Among the European plans, only the SDDR covers both a 15-year period until 2040 and network needs for voltage levels up to 63 kV.
According to the report, investments proposed in the RTE plan, compared to the size of the French electricity system, appear to be lower than in most countries in the comparative analysis. These differences can be explained by various factors such as differences in the prospects for deploying production or electrification resources, a better distribution of these resources in relation to consumption households, the structure of the network and an initially less congested network, etc.
Overall, RTE has defined three major challenges for the network development strategy – the connection of electricity production and consumption facilities, the adaptation of the structure of the major transmission network and the adaptation of the network to climate change based on the renewal programme. In order to overcome these challenges and take the leap forward towards decarbonisation and reindustrialisation, it is of utmost importance that the SDDR is timely and effectively implemented.
Figure 1: Summary of RTE’s reference strategy and possible alternatives
Figure 2: Key highlights of RTE’s reference strategy and alternatives (EUR billion)
