As production ramps up, led by the car and electronics industries, battery capacities are increasing and prices are falling.

In late November, for instance, Samsung Electronics, a big south Korean firm, said that by incorporating graphene-an lutra-thin form of carbon –
into a lithium -ion battery, it had managed to boost its energy capacity by 45% and greatly decrease the time needed for a recharge.

Many other new battery chemistries are being developed. One promising idea is a solid-state lithium battery, which replaces the liquid electrolyte of current cells with a solid substitue.

Besides offering much higher energy densities,such batteries should also be cheap to mass produce. Those trends, think Dr Kumar, would allow his aircraft to increase its range to around 2.400KM

by 2035, and perhaps even ditch the on-board generator.

Combining all these benefits and drawbackers.