Dressed in an immaculate dark suit, 72-year-old Prem Jain stands outside the offices of Spectral Services Consultants, the Delhi-based engineering firm he founded in 1980. Mr Jain, white-haired and soft-spoken, doesn’t mind the blazing afternoon sun that bakes the dusty streets of Noida, the fast-growing satellite city near Delhi where Spectral is based.

He beams as he estimates that Spectral’s squat four-storey offices use less than half the electricity of a similar-sized building next door.