Science and Technology
The trains of the Rennes metro will partially run on solar electricity starting in early 2027, in a project that is unprecedented in the history of French urban transport. The technical difference that makes the venture pioneering is not simply using solar panels, but injecting the electricity produced directly into the trains’ electrical circuits, without the energy passing through the public distribution network. David Clausse, General Director of the Departmental Energy Union 35, explained that having the necessary technical knowledge to ensure that the produced electrons do not disrupt the trains’ operation was the biggest challenge of the project.
The crowdfunding campaign was launched on May 18, 2026, and runs until the 30th. Citizens can invest between 100 and 10,000 euros, with a fixed return rate of 5% per year for five years. Construction of the solar plants begins in June, and the trains are expected to start running on solar energy between the end of 2026 and the beginning of 2027. Rennes, with about 230,000 inhabitants, is the smallest city in the world to operate two metro lines, and now it may become the first to power its trains with the sun.
The project plans for the installation of two photovoltaic plants at the ends of the two metro lines in Rennes. The first will be in Chantepie, on the roof of the garage and workshop complex of Line A. The second will be installed in Saint-Jacques-de-la-Lande, at the La Maltière terminal of Line B. In total, 6,000 square meters of solar panels will be distributed over the roofs of the garages and adjacent parking lots.
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The energy generated will be channeled directly to the electrical circuits that power the trains, stations, and signaling systems. There will be no connection to the public electricity grid. Clausse explained that this disconnection is what makes the project unprecedented: in other cases of solar energy in transportation, the electricity is sold to the grid and then repurchased. In Rennes, the electrons go from the panel to the train motors without intermediaries.
The Chantepie plant is expected to generate more than 500 megawatt-hours per year, while the Saint-Jacques-de-la-Lande plant will produce about 400 megawatt-hours. Together, the two installations will provide nearly 1 gigawatt-hour annually, enough to supply 7% of all the energy consumed by the trains on lines A and B of the Rennes metro.
The total cost of the project is 1.6 million euros. Part of the resources comes from European funds, and 500,000 euros were opened to crowdfunding. Valérie Faucheux, vice-president of the Rennes Metropolitan Area responsible for mobility and transport, stated that the logic is clear: producing locally allows for controlling expenses in a scenario of volatile energy prices. The goal is aligned with the Territorial Climate, Air, and Energy Plan, which aims to double the production of renewable energy in the territory.
The opening of crowdfunding to citizens is not just a resource-gathering strategy, it is a form of community engagement. The campaign allows anyone to invest between 100 and 10,000 euros in the project, with a guaranteed return of 5% per year for five years. Initially, priority was given to the metro users of Rennes, who can concretely participate in a local clean energy project.
The participatory financing model for transportation infrastructure is relatively new in France and reflects a European trend to democratize investment in renewable energy. For a citizen who invests 1,000 euros, for example, the return is 50 euros per year, totaling 250 euros in five years in addition to the invested capital. The amount is modest, but the symbolism is strong: passengers who finance the solar panels know that the trains they use daily run partly on the energy they helped to install.
Rennes was already notable for operating a fully automated, driverless metro system with Siemens’ VAL and NeoVal technology. Now, by adding direct solar energy to the trains, the city creates a model that can be replicated by any metro system that has garages or parking lots with roofs available for photovoltaic panels.
The limitation is evident: 7% of the energy is a small fraction of the total consumption. But the project demonstrates that the technology works and that the direct injection of solar energy into transportation circuits is feasible without compromising train operations. If the model is expanded with more panel surfaces or combined with battery storage, the solar share can grow significantly in metro systems around the world.
Would you invest money in solar panels to power the trains in your city? Do you think the Rennes model could work in Brazil, or is the reality of our metro systems very different? Tell us in the comments.
I cover construction, mining, Brazilian mines, oil, and major railway and civil engineering projects. I also write daily about interesting facts and insights from the Brazilian market.
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