Larry Niven's "Known Universe" (KU) features "The Outsiders" as one of its most prominent alien races.
As per KU canon, the Outsiders evolved in a frigid moon (similar to Nereida) and they sustain themselves by generating electricity via thermal differentials, placing one part of their bodies in frigid darkness and another on a light source (thus creating a thermal differential). An "Outsider" is in essence a living thermocouple.
In an infinite universe everything is possible I guess, and in a fictional world, "my rules" rule.
However, I try to consider the feasibility of such an evolutionary approach. How could one put some rigor into the development and evolution of such an species, that it could lever such a metabolic approach to evolve not just life, not even complex life, but sentient life (which I'd think is a very metabolic intensive process.)
Any ideas how I (or one) would go about that? Suggestions?
Obviously, there'll be some hand waving and suspension of disbelief, but I'd like to see/use some hard science into this.