(I) A dramatic cut in the cost of a super-efficient new breed of solar cell could put domestic solar power on a more economic footing. (II) The cells, which helped take NASA's electric-powered aircraft Helios to record altitudes, have until now been too expensive. (III) But their manufacturer has found a way to make them as much as 20 times cheaper. (IV) The cells convert light energy into electricity with an efficiency of 20 per cent – which means they generate one-third more electrical power than conventional silicon solar cells. (V) NASA's electrically powered plane Helios soared to altitudes above 96,000 feet (29 kilometres) – a world record for a winged plane not powered by a rocket engine.