Single kite and kite train already flew at high altitude, respectively 4422 m in 2000 and 9740 m in 1919.
And also the Zhonglu High Altitude Wind Power Technology - 中路高空风力发电技术 projects has at least demonstrated that it was possible to add one aerostat to the kite train.
The main problem with photovoltaic energy is that sunlight can be obscured by clouds, which makes electrical production intermittent and uncertain. But above the cloud cover, the sun shines all day, every day. Anywhere above the planet, there are very few clouds at an altitude of 6 km—and none at all at 20 km. At those heights, the light comes directly from the Sun, as there are no shadows and hardly any diffusion by the atmosphere. As the sky loses its blue color, direct illumination becomes more intense: the concentration of solar energy results in more effective conversion, and hence higher yields.1
Under these conditions, the energy source is five times more abundant than on the ground,2 and production is entirely predictable. So why not send solar cells up above the clouds,
Five times in average power (far more time of sunlight as already mentioned), this is not negligible. Sure this involves to very long tethers, a little like some AWE projects like Sky Windpower for which I have never heard of any impossibility from AWE players, but only from Mike Barnard.
But if we want avoid these very long tethers, lower altitudes would allow to keep another advantage (losing 5x advantage) which is avoiding saturation of solar panels on the ground, and the high cost on roofs that leads to the preference of solar installations on the ground (see above).
The major advantage with flying solar panels in regard to current ground-based solar installations, is the possibility to increase the total of solar panel area.
The major advantage with flying solar panels in regard to current testing high altitude wind for electricity production, is avoiding the drag which is inherent to electricity generation by wind, and which lowers the elevation angle.
This is all the problem with AWE and likely the main reason why it don’t succeed.
The energy is maximum in the horizontal: the more we go up, the more powerful the winds are, but the more we lose in efficiency, first by cosine loss³.
With stationary flying devices equipped with solar panels, there is no cosine loss since only the lift force of the high winds is used, by Bernouilli’s principle. The benefit of higher and higher winds is a net benefit, apart from the total mass and drag (less for a static aircraft) of tether.
I think these arguments must carefully be studied in a AWE world which persists in denying the problems of land and space use due to a low elevation angle and which would lead to an impossibility for massive marketing, in the unlikely event of efficient working in the time.