There's no sense letting it get rained on, so it needs some sort of cap (especially given that it's presumably electric high powered lasers).
It doesn't seem to move fast enough to care about wind resistance.
A cube is a nice easy shape to build... so why not a cube.
Elsewhere in this comment section someone pointed out that the generator on this supplies slightly more energy than the rated maximum of most houses. It only has a few sq m of solar space on it for solar panels... that doesn't seem like it will even be a dent.
Like usual, you're better of putting solar panels on the ground somewhere. If this thing ever becomes electric I think it will have to either be by a wire, or by using electricity to convert CO2 back into fuel. Maybe if batteries improve a bit by battery, but right now it sounds like it would need to spend a large portion of it's time recharging (just comparing to electric vehicles).
On the flip side - this might be a great candidate for these guys carbon capture technology: https://news.ycombinator.com/item?id=26412624
Really cool product!
I think what this product may lack if anything, is some RGB LED lighting and a name with X or Z in it, eg "CarbonX LASER-Z". Especially now with eSports increasing popularity, perhaps we may find eFarmingSports finding a niche, where the most zapped weeds per time unit wins.