Guardian: The Chinese county of Guazhou, in north-western China, is famous for its honey melons. But it also produces wind. It blows in from the east through the high, narrow valley formed by the Qilian and Beishan mountains, on the southern edge of the Gansu Corridor. When the wind reaches Yumen, a city east of Guazhou, it has an average speed of 7.9 metres per second and energy-density of 506 watts per cubic metre at a height of 70 metres. By the time it gets to the "world’s wind warehouse" …