The most common and most likely answer to this crossword clue is the 7 letter word BIOFUEL
I've seen this crossword clue in The Times
B
I
O
F
U
E
L
More clues leading to the result BIOFUEL
Buddy explains!
The straight part
We know that "that avoids putting fossils into power" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case that avoids putting fossils into power = biofuel.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 BIOFUEL mean?
BIOFUEL noun- Any fuel that is obtained from a renewable biological resource, especially from biomass