Energy is not a thing; it is a rate of delivery versus rate of usage.

In olden times, energy was something substantial that you could carry around such as a cord of wood. But nowadays, with the advent of electrical developments, energy is not something that you carry around, nor is it something that can be destroyed or used up.

Energy is the rate of its delivery versus the rate of its usage. And if its rate of delivery should exceed its rate of usage, then (for all intents and purposes) it will appear to be limitless even though it does not have to be limitless in order to satisfy that ratio.