TL;DRPower you modular armor the steampunk way
What ?A steam engine for use in modular armor. Just add fuel and you get plenty of power for all your gadgets
Why ?It is barely possible to use many of the modules for modular armor before geting the late game portable fusion reactor. Even when filling most of the space in the armor with solar panels the power is not enough to run a personal roboport, for any length of time. Mining the robots is currently the only practical way of doing this, but that feels more like an exploit.
A portable steam engine could fill this gap, and enable the use of modular armor earlier in the game. With the added inconvenience of having to refuel it periodically.