The most common and most likely answer to this crossword clue is the 8 plus 7 letter word RESEARCH STATION
I've seen this crossword clue in The Times
R
E
S
E
A
R
C
H
S
T
A
T
I
O
N
Buddy explains!
The straight part
We know that "Troll is lonely one" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case troll is lonely one = research station.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.