China has flown an airborne wind energy system to 4,000 metres (13,123 feet) above sea level and generated electricity from the sky, in what state broadcaster CCTV described as a world first.According to a CCTV report on Saturday, the prototype S4000 craft completed a full work cycle – ascent, station-keeping, power generation and recovery – at a test site in northwestern China, which the broadcaster called a breakthrough for high-altitude wind power and a step towards engineering deployment.The craft, which is roughly the length of a Boeing 747 and resembles an airship, is filled with helium and floats into the sky carrying lightweight turbines. From a high altitude, it can harness stronger, steadier winds and send the electricity it generates back to the ground through a tether.The craft can also be moved quickly between sites, making it suitable for providing electricity in remote locations such as deserts, highlands, islands and disaster zones beyond the reach of a power grid.The S4000 was developed by Beijing start-up Sawes Energy Technology in collaboration with Tsinghua University and the Aerospace Information Research Institute of the Chinese Academy of Sciences.The craft, roughly the length of a Boeing 747, is filled with helium and harnesses winds at a high altitude to generate electricity. Photo: CCTV