Wiktionary
n. A source from which useful energy can be extracted or recovered either directly or by means of a conversion or transformation process (e.g. solid fuels, liquid fuels, solar energy, biomass, etc.)
Usage examples of "energy source".
Both elements are plentiful, and it seems far more likely to me that human ingenuity and a sufficiently concentrated energy source will produce cheaper, more convenient alternatives long before the last barrel of the stuff we're squabbling about today is pumped out of the ground.
In that period the best energy source for satellites or interstellar probes was the atomic micropile.
It would have been a powerful signaling unit, automatically operated from the increasing energy source of its dying sun, that would transmit at ail known radio frequencies up to, perhaps, a distance of two light-years - signals that the spaceship crew of any other advanced technology would recognize as unmistakably artificial in origin.
The specimen that was supposed to prove antimatter was a safe and viable energy source had been stolen.
While the Companion hadn't been working any direct magic, she had been acting as an energy source for both of them, plus giving the more timid creatures a good scare when she charged them.
Returning to the dead Gyrgon, she began to peel off his exomatrix in an attempt to discover whether, as in the case of the sleep chamber, there was any kind of energy source she could salvage.
Marc carried the equipment to his chair by the fire, plugged the helmet into its energy source, and fiddled with the handset.