The S1500 floating turbine’s operating altitude is 4,921 feet above ground level, where wind speed moves about three times faster than at the surface. The advantage of this altitude (also referred to as vertical slice) can result in a power output up to 27 times higher than a conventional ground-based wind turbine of similar capacity.
The capacity to generate one megawatt of electrical power (MW) with the S1500 system is comparable in size to what small wind power turbines normally generate (a conventional 328-foot-tall wind turbine), while the footprint of the S1500 system is significantly smaller. This amazing power density shows the efficiency benefits of being able to access high altitude wind power resources by new and innovative airborne platforms.
From the article the turbine unit weighs 2204lbs so that's ~9400 lbs total. Omni calculator says you need 348,436 standard 11" party balloons or 3,979,252 litres of helium to get off the ground and 423,779 party balloons to reach 1.5km altitude.
It can’t weigh 2,204lbs if it floats it should weigh approximately -7,200lbs if it’s going to carry the cable and rope.
I'm assuming that's the weight of the turbine without helium in the balloon.
So it would be even lighter if you filled it with hydrogen?
Which would be the way to go, since no humans are on board and it’s probably not made out of s aluminum doped cotton.
Could you not add wings for additional lift?