In the same idea, I made myself a big wheelbarrow for gardening or cleaning the park of horses (with an old trash container reformed, 500 l anyway!), And when it is full, I admit that it is a bit heavy!
I am designing a system to adapt a wireless tool to make it self-propelled. I'm just going to fix a grinder gear hs, with a rod to drive the wheels by fixing my screwdriver.
it would be no less complicated to harness the horse?
hay is more renewable than lithium!
on the other hand too well the mini bike link with power drill!
and very nice your wheelbarrow!