Règle correspondante
Practice Relating to Rule 8. Definition of Military Objectives
Section G. Economic installations
Sweden’s IHL Manual (1991) states:
How and to what extent a given object can effectively contribute to the adversary’s military operations must be decided by the commander. This need not imply that the property in question is being used by the adversary for a given operation … It may even be a question of … energy resources or factories that indirectly contribute to the adversary’s military operations. 
Sweden, International Humanitarian Law in Armed Conflict, with reference to the Swedish Total Defence System, Swedish Ministry of Defence, January 1991, Section, p. 54.