Phoenix Logs/Banished Buildings/Power Extractor
From Halopedia, the Halo wiki
Massive channels for power criss-cross the Ark, and carefully sited facilities can dig into these channels and safely siphon a tiny fraction of their potential. which is accumulated as Power. The Augmented Extractor upgrade significantly improves Power collection, which is of vital importance when threats to the Banished and their mission begin to multiply.
The siphoning and filtering of energy from the Ark is not subtle, but it is surprisingly efficient and causes only relatively small disturbances in the installation's ambient security grid. Nevertheless, no power extraction facility operates for long without attracting the attention of Aggressor Sentinels, which begin to escalate the outpost's threat level to the Ark and the scale of the reaction.