India’s massive diesel-guzzling railway network is getting serious about its experiments with solar.

On July 14, Indian Railways rolled out its first train with rooftop solar panels that power the lights, fans, and information display systems inside passenger coaches. Although the train will still be pulled by a diesel-powered locomotive, a set of 16 solar panels atop each coach will replace the diesel generators that typically power these appliances. The railways estimate that a train with six solar-powered coaches could save around 21,000 litres of diesel every year, worth around Rs12 lakh.

In 2014, Indian Railways consumed 2.6 billion litres of diesel, accounting for around 70% to the network’s total fuel bill of Rs28,592 crore.

The first of these trains will be pressed into service on the suburban railway network of New Delhi, one of the world’s most polluted cities, before two dozen more coaches are fitted with similar rooftop solar systems. Retrofitting each coach with these system, including an inverter to optimise power generation and battery for storing surplus power, costs around Rs9 lakh.

The rooftop solar system was developed by Noida-based Jakson Engineers, under the direction of the Indian Railways Organisation for Alternate Fuels (IROAF). ”It is not an easy task to fit solar panels on the roof of train coaches that run at a speed of 80 km per hour. Our engineering skills were put to a real test during the execution of this rooftop solar project for Indian Railways,” Sundeep Gupta, vice-chairman and managing director of Jakson Engineers told the Business Standard newspaper. Established in 2008, the IROAF initially focused on bio-diesel and compressed natural gas (CNG) to help diversify Indian Railways’ fuel mix, before looking at solar.

Indian Railways has ambitious plans for solar. By 2020, the state-run transportation network plans to generate around 1,000 megawatts (MW) of solar power, which could be scaled up to 5,000 MW by 2025. These numbers are not only significant for the railways, given that it’ll help bring down the fuel bill, but will also impact India’s overall renewable energy goal of 175 gigawatt (1 GW = 1,000 MW) by 2022.

So far, Indian Railways has made limited progress. Out of its 1 GW solar target, only about 16MW of capacity (pdf) has been installed, as of March 2017. However, nearly 255 MW of rooftop and 250 MW of land-based solar projects are in the pipeline, with around 130 MW of capacity already awarded.