The sun, albeit indirectly.

By that logic a Hummer is carbon neutral.

Then anything that doesn't use fusion/fission to make carbon is carbon neutral.

Also, what about the carbon output for the cart, equipment, and consumables?

I'm very excited about this aspect and their focus on being CO2 neutral. I'm not entirely convinced yet and would be interested to know the energy source split (particularly more about how they use the NBG).

Also allowing people to charge their phones is a given really but that's got to be super fast charging otherwise it could get awkward... XD