A Swiss startup installed retractable solar panels on an active SBB train line in April 2025 — and the trains kept running. If it scales, Switzerland's 3,300 km of track could generate more power than a mid-size coal plant.
There is a long, thin strip of land that nobody thinks about much. It runs the entire length of every railway line in the world — the strip between the tracks. On a standard-gauge railway, this gap is roughly 1.4 metres wide, stretching for kilometre after kilometre, sheltered from road traffic, fenced off from animals, and sitting in full sun. For 200 years, railways used it for exactly nothing.
A Swiss startup called Sun-Ways has decided to change that.
The installation nobody expected to work
On 24 April 2025, Sun-Ways — a spin-out from the École Polytechnique Fédérale de Lausanne (EPFL), one of Europe's top engineering universities — completed the installation of the world's first solar panels built into an active railway track, on a regional SBB line near Buttes in the canton of Neuchâtel. The line did not close. The trains did not stop running. Engineers simply slotted photovoltaic panels into the gap between the rails, anchored them to the sleepers, and connected them to the grid.
The system generated power. The trains passed over it without incident. The panels survived.
The key innovation that makes this possible is a retractable design. Each panel unit can slide sideways out of the track geometry in under four minutes, allowing maintenance vehicles — tamping machines, inspection cars, ballast cleaners — to pass through without disturbing the installation. This solved the problem that had defeated previous researchers: railway tracks are not static infrastructure, they need regular maintenance access, and anything installed between them has to get out of the way.
The numbers
At full deployment, Sun-Ways estimates the system can generate approximately 48 kilowatt-peak (kWp) per kilometre of track. Switzerland's national railway SBB operates around 3,300 kilometres of track. If panels were installed across the entire network — which will not happen all at once, and some sections are unsuitable — the theoretical peak output would exceed 150 megawatts, enough to power a small city or run a significant fraction of SBB's own energy needs.
More practically, the pilot near Buttes is sized at around 18 square metres across 100 metres of track. It will be monitored over two years for panel degradation, vibration effects from passing trains, soiling from diesel engines and ballast dust, and electrical safety under load. EPFL researchers are leading the technical evaluation. SBB has approved the site and is watching the results.
Sun-Ways is not the only company working on this concept — a Belgian firm called Voltera, backed by railway company Infrabel, is pursuing a similar system — but the Buttes installation is the first to go live on a functioning mainline.
The Indian angle
Indian Railways has approximately 67,000 kilometres of track — about twenty times Switzerland's network. It is also one of the world's largest electricity consumers, running on a mix of grid power and diesel traction that costs tens of thousands of crore rupees annually. Indian Railways has already installed rooftop solar on stations and freight wagons as part of its Mission 100% Electrification programme and a net-zero carbon target by 2030.
If between-track solar proves viable at Swiss scale, the pitch to Indian Railways becomes clear: the land already exists, it is already secured, and the sun in Karnataka and Rajasthan is considerably stronger than in Neuchâtel. Namma Metro itself operates approximately 175 kilometres of track across Bengaluru. Even a fraction of that converted to solar generation would meaningfully reduce BMRCL's energy bill.
None of that is happening in 2026. The technology is still in pilot. The maintenance interference question — Indian Railways runs far heavier tamping and ballasting cycles than SBB's lightly trafficked regional lines — is unresolved. But the concept is no longer theoretical.
The simple idea that took decades to arrive
In retrospect, the idea is obvious. Railways own long corridors of south-facing open land in temperate countries. Solar panels need exactly that. The engineering problem — how to make panels survive vibration, maintenance access, and high-speed air pressure waves from passing trains — was genuinely hard. Sun-Ways says the retractable design, combined with a shock-absorbing mounting frame developed with EPFL, is what finally made it practical.
The Buttes pilot runs until at least 2027. If the data holds, Sun-Ways plans to scale to a one-kilometre section on a higher-frequency line, the real stress test for the technology.
For now, somewhere in a quiet corner of Switzerland, trains are running over solar panels that are quietly generating power. The gap between the rails — two centuries of wasted space — is finally earning its keep.