Energy – is a suorce of power, such as fuel, used for driving machines, providing heat, etc. And energy is ability of matter.
The word "Power" has a lot of meanings, but in this context there are:
1) energy that can be collected and used to operate a machine, to make a electricity, etc (nuclear/wind/solar power)
2) the strength or energy contained in smth.
by Oxford Advanced Learner's Dictionary