Okay, so the primary theme of The Undiscovered Country is not energy use, it’s race relations, BUT energy use does play a principle role in the narrative. The film opens with the destruction of the moon Praxis, which is the primary dilithium source for the Klingon Empire. According to Spock, the destruction of Praxis was caused by over-mining and insufficient safety precautions. The debris from Praxis is polluting the ozone of Kronos, the Klingon home planet, which will cause the oxygen to be depleted on Kronos in 50 years. This is an example of a stronger force (the Klingons) subjugating a weaker force (the environment,) and as is common with energy narratives, the environment seeks its revenge. Now with Praxis gone, the Klingons have neither the dilithium to fuel their ships nor the safety of their people.
The Klingons have been at war with the Federation for 70 years, though they are currently at an armistice. Spock says that the Klingons cannot both maintain their hostilities against the Federation and save their planet. Thus, the Klingons have agreed to peace negotiations with the Federation.
The narrative also makes mention of a labor issue involving dilithium production. Kirk and McCoy are sentenced to a penal colony on Rura Penthe to mine dilithium for the Klingon Empire. Being sentenced to this penal colony is well known as being the same as an execution sentence. The prisoners are forced to work under extreme conditions and those who do not work are left to freeze outside the camp:
“Work well and you will be treated well. Work badly and you will die.”
Hard labor prison camps are just another form of convenient bigotry, like racism, to help find laborers that can be mistreated in order to ensure profit. In addition, The Undiscovered Country contains the same life and energy equivalency theme found in the episodes of Star Trek that I have written about thus far. The Klingons know that the conditions on Rura Penthe are so extreme that they will eventually kill the workers. Life pays for energy.