Official Entry: "Energen builds power stations which use fusion power cells to generate energy. This is an alternative but cheaper large scale power system than equivalent Elerium units. However, the corporation is wary of attempts by Solmine to create cheaper Elerium energy systems. This can only be achieved by lowering the price of Elerium which could happen if the rebellious mining colonies are totally subdued."
Energen does not sell any products useful to X-COM; hostile relations will not result in X-COM's power being cut.