The most common and most likely answer to this crossword clue is the 5 letter word JUICE
I've seen this crossword clue in The Times
J
U
I
C
E
More clues leading to the result JUICE
Buddy explains!

The straight part
We know that "energy" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case energy = juice.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does JUICE mean?
JUICE noun- A liquid from a plant, especially fruit.
- A beverage made of juice.
- Any liquid resembling juice.
- A soft drink.
- Electricity.
- Liquor.
- Political power.
- Petrol; gasoline.
- Vitality.
- The amount charged by a bookmaker for betting services.
- Steroids.
- Semen.
- The vaginal lubrication that a woman naturally produces when sexually aroused.
- Musical agreement between instrumentalists.
- To extract the juice from something.
- To energize or stimulate something.
- Alternative spelling of Jew's (used in certain set phrases like juice harp)