An apparatus that is usable with a well includes an operator and a generator. The operator is disposed in the well and configured to respond to a differential pressure between hydraulically isolated zones of the well to produce mechanical motion. The generator is disposed in the well to convert the mechanical motion into electricity. A method that is usable with a well is provided including maintaining hydraulic isolation between a first and second zone of a well. While maintaining the hydraulic isolation, the method further includes producing a mechanical motion in response to a differential pressure between the first and second zones and generating electricity in response to the mechanical motion.