A solar roof with 4,400 panels has been unveiled on Blackfriars Bridge in central London.
Network Rail said it was the world's largest solar bridge and would provide up to 50% of Blackfriars station's energy.
The roof above the Victorian bridge is part of a £6.5bn programme to increase capacity on the Thameslink route.
Network Rail said the panels would "reduce the cost" of running the station.
Simon Kirby, the managing director of Network Rail Infrastructure Projects, said the transformation showed how the route was being enhanced by "using smart, sustainable technology to reduce the cost of running the railway".
The Thameslink route runs from north to south of the capital through central London.
The panels cover an area of 6,000 sq m and are expected to generate 900,000 kWh of electricity every year, saving over 500 tonnes of CO2 annually.
Blackfriars station was revamped as part of the Thameslink programme and opened in 2012 with longer platforms and new entrances on the Southbank and Bankside.
First Capital Connect, which runs Blackfriars station, said the new roof would give passengers "an even more sustainable journey".
Managing director David Statham, said: "The distinctive roof has also turned our station into an iconic landmark visible for miles along the River Thames."
Blackfriars is the first bridge over the Thames since the London Bridge to generate its own power.
Built in the thirteenth century, the bridge used water wheels to drive pumps and grain mills.