In Noida, a burgeoning satellite city on the outskirts of the Delhi megalopolis, Kushagara Nandan runs Sunsource Energy, a solar start-up. Educated in the US, he cut his teeth on a similar outfit based in New Jersey. Last year, SunSource revenues quintupled, to £6m.

Part of his business is supplying rooftop units which, when the sun is shining, can fill the gap caused by grid outages far more cheaply than diesel: “We synchronise grid, diesel and solar together. In Delhi alone, the potential for rooftop solar is at least 1.5GW.” One of his projects, rated at 250KW, adorns the Habitat Centre, a complex that includes conference venues, auditoria, restaurants and art galleries. Another 500KW array has allowed a school to save 20% on its power bills.

Cheap, off-grid solar also has great potential in India’s vast rural hinterland. Last year, a solar project to desalinate briny ground water from wells and power irrigation pumps at a village in the southern state of Andhra Pradesh, which Sunsource helped develop with an Indian NGO, was given a Google Global Impact Challenge award. It worked so well that it has now been rolled out in five different villages.

Read the complete story in The Guardian