India’s railways are a bit of a success story. The network is massive, and entirely state-run, and, in the past financial year, carried a total of 8.4bn passengers. That’s more than 23m people a day.

These trains, as you’d imagine, use up quite a bit of fuel. Around half the locomotives currently held by Indian Railways (IR), the train operator, still run on diesel, and fuel costs the operation around $5bn a year.

And so, to bring these costs down, IR is looking to source 10 per cent of its energy from renewable sources by 2020.

The most exciting proposal so far is to mount solar panels on the roofs of train carriages in order to power lighting inside, and eventually even air conditioning, inside. The panels are currently being tested on a train that runs between Rewari and Sitapur, a city and town in northern India.

Each solar panel coach should save IR around $2,000 a year, which means they’ll need to be used for just over three years to offset their initial cost (just over $6,000 per carriage). 

The network also hopes to open solar power plants in 200 train stations and some of its offices, which would do even more to lower emissions and cut costs. Across India, meanwhile, prime minister Narendra Modi is attempting to increase the country’s current solar power generation by a factor of five by 2022. Full speed ahead.

Here’s one of the test carriages:

H/t: Quartz