"High-altitude winds between 1,640 and 3,281 feet (500 and 10,000 meters) above the ground are stronger and steadier than surface winds. These winds are abundant, widely available, and carbon-free.
"The physics of wind power makes this resource extremely valuable. “When wind speed doubles, the energy it carries increases eightfold, triple the speed, and you have 27 times the energy,” explained Gong Zeqi "
Oh sorry, I think I was responding to someone else. As for cable weight, I was playing around with this calculator and for a pure copper wire less than 3mm thick and 10km long, you only need to overcome 300kg in weight.
If you use the standard 20mm wide cables, then yes weight becomes a huge problem. But then maybe you use more balloons, or just secretly hook it over a few satellites when no one’s looking