I conceived and used the solar balloon jumping as a (dangerous) game, not for any other use.
The balloon accelerates while it gets up during the 10 m rope. The obtained kinetic energy is: 1/2 V² x m where V is the balloon vertical speed in m/s (here 3 m/s), m is its mass (envelope = 10 kg + air = about 450 kg for a 400 m3 balloon = 460 kg).
1/2 x 9 x 460 = 2017 J.
The buyoancy is 200 N. So the weight is 800 N - 200 N = 600 N.
The jump height is 2017/600 = 3.45 m.
A 400 m3 double envelope balloon is shown on the first video. A 800 m3 single black envelope is shown on the second video.