Reactor Facility
In terms of criticality, the reactor facility is only second to the command centre. The efficient extraction and distribution of geothermal energy is the primary resource to manage across the battlefield, which is supplemented with secondary energy reserves from wind farms.
It is usually the second facility built but don’t be tempted to rush the process and build adjacent to the command centre just to get it operational as quickly as possible! The efficiency of the reactors is, in part, driven by the thickness and composition of the crust at a given location. Equipping your deployment bot with an environmental scanner (and upgrading that scanner as quickly as possible) will start to build a resource heat map that shows you the optimal build sites as well as those best avoided. Choosing the correct location can double or even triple the amount of power a reactor can provide per unit time!
Be sure to also think about the placement of your reactors as your forces expand across the island. As all facilities and most outposts have at least three interfaces, as much as possible you want to plan for multiple, diverse routes of power to each building. Having a long chain of buildings stretching across the island may help you cover territory more quickly, but what happens if one building in that chain is lost and you have no alternate paths? Suddenly you have a number of facilities and outposts, potentially behind enemy lines, running on internal power only which may be enough to keep the lights on for five minutes or so.
Additionally, if a building is disconnected from the RTN and has no path back to a command centre, you can’t issue any new orders to that unit, and it will be unable to forward orders on to any mobile units in comms range.
When it comes to planning the topology of the resource transfer network, play for the long game, not the quick wins; it is the single most important resource you own.