The generator is a station facility that makes power by burning fuel from the station's hold. A new station has no power, so its first facility is always a generator. It is built from iron ore, which the hull can mine from the start.
Behaviour
Generators take their own slots, separate from the facility slots, and every station allows them. Each tick the station switches on as many as it needs, in priority order, to cover the facilities that are running work. Idle facilities draw nothing, so a station with no running work burns no fuel. Always-on facilities are the exception: uplinks, repeaters, firewalls, monitors, data warehouses, defence batteries and sensor arrays draw power all the time, and do nothing without it.
A generator that is switched on burns fuel once a minute, and the fuel becomes exhaust. If the hold runs out, work waits: recipes stop progressing and the facility shows as paused until fuel arrives. Nothing is lost.
Research
A trialled generator design with enough power output unlocks the fusion reactor.