The expansion pack commander has an aura that syphons ship energy from creatures killed within its radius. It’s the energy that powers the ship weapons, displayed in little glowing squares below the Commander control icon.
The energy syphon aura is tied to the commander’s Psi stat, and increasing Psi will increase the aura’s radius. With it maxed out you can sometimes get two or three squares of ship energy per enemy wave, so you can use your ship weapons much more frequently.
Hope that helps 