As for late game, obviously you don't have uranium at this time, but that could be added and form the basis of fission power plants. Or when you get the mini-fusion power plant for the modular armor? Why isn't there a full sized fusion power plant? That'd make a lot of sense. And be really expensive to make, but so's the mini-fusion.
And for the more environmentally friendly, how about orbital solar beamed power? Add in for the militarily minded, a solar pumped laser to attack ground based targets
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