Low energy systems are obviously preffered, but it becomes a trivial concept once you start generating at scale - what does become an issue is thermal dissipation - space lacks matter for conduciton/convection, typically. That's the energies you want to try and keep low, then the thermal dissipation systems can have an easier time and scale smaller. If you've a cunning design for a electrochemical (electrocatalytic) biomass fuel cell, these might be able to assist in powering habitation facilities. But hopefully it can be engineered to be able to beam power anywhere.
I'm still not overly clear what you'd mean by "planting machine".