The power purchase agreement (PPA) was for the supply of 88 gigawatt hours (GWh) of power per year to DB from four run-of-river plants in Sweden, Deutsche Bahn said in a statement.

"As a result of the energy transition, we are not only decarbonising our own power generation but are also making more green power available to our customers today," said Carsten Poppinga, Uniper's chief commercial officer.

Deutsche Bahn, Germany's single biggest power consumer, seeks to reach a target of 80% of renewably sourced electricity by 2030. It currently sources 68% of its energy needs from renewable sources, compared to 55% in Germany as a whole last year. The rail operator also has supply contracts with Uniper peer RWE and others.

State-owned Uniper, meanwhile, is on a transition course away from a fossil fuel-heavy past to cleaner energies in production, marketing, trading and storage.

Uniper wants 80% of its power station capacity to be carbon-free by 2030, mainly by transforming its natural gas-to-power plants successively to green gases.

Green PPAs have become an essential part of the company's product range to assist commercial buyers in reducing their carbon footprint while also allowing the customer to reliably forecast costs in what continues to be a volatile energy market.

PPA contract prices are not typically published, except for some information available from price trackers.

Sweden and Germany have power cable links for imports and exports, but real cross-border capacities are no hindrance to PPA delivery contracts, whose set-up allows both sellers and buyers flexibility in arranging fulfilment.

Deutsche Bahn is under pressure to modernise its ageing infrastructure to help Germany meet national climate targets and make rail travel more attractive.

(Reporting by Vera Eckert, editing by Miranda Murray and Ros Russell)