The Energy Grid is an energy layer lying beneath real space and between the hyperspatial regions. A Mind taps it directly; the supply is so large relative to anything a Mind might want to do that energy effectively ceases to be a constraint — one of the technological foundations of post-scarcity itself.
The same access lets ships and habitats draw on colossal reserves for propulsion, manufacture and, when it comes to it, weaponry. Related: Hyperspace, General Systems Vehicle.