One way to amass T-Energy is keep fighting the giant crab enemy in Marshall's Gorge after you receive the Acetylene Torch upgrade for your rig. Defeat the crab, fast travel to any location, then return to the Gorge again to respawn the crab and kill it again for T-Energy. However, it's important to note that you will no longer be able to make the crab respawn once you complete Marshall's Gorge, so be sure to take advantage of this trick while it lasts.