What if player buys from another some machines , highly overclocked and want energy for that?
anyway, trading energy is good for many purposes. [And with that you can "teleport" energy to far-away outposts (Teleporter + EM-X)]
EM-0 was supposed to be a joke, so don't consider it. (Free energy condensing is too cheaty)
Energy condensing is supposed to be not 100% efficient, similar to electrolizer.
In my opinion electrolizer can be reworked to work this way and can use tin cells to store EM-X
Discharging them in another energy condenser keeps cell, directly inside MFSU/MFE/Batbox maybe.