You are rightm but we can use Biogas in the burners, since the amount of fuel is negligeble compared to an engine. It is not avalible in all places yet though.
But it's not up to us. It's like someone who charges an electrical car with a diesel engine. How could Tesla police that? They would need thousands of private investigators, and we all know the quality of work of private investigators.
I don't understand -- the primary function of the cart is to make coffee, right? And it's impossible for the cart to carry out this primary function without some source of combustable fuel, yes?
If that's the case, there's no honest way you can claim it's "powered only by the sun and your own body".
